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W3C

XQuery 1.0: An XML Query Language

W3C Working Draft 23 July 2004

This version:
http://www.w3.org/TR/2004/WD-xquery-20040723/
Latest version:
http://www.w3.org/TR/xquery/
Previous versions:
http://www.w3.org/TR/2003/WD-xquery-20031112/ http://www.w3.org/TR/2003/WD-xquery-20030822/ http://www.w3.org/TR/2003/WD-xquery-20030502/
Editors:
Scott Boag (XSL WG), IBM Research <scott_boag@us.ibm.com>
Don Chamberlin (XML Query WG), IBM Almaden Research Center <chamberlin@almaden.ibm.com>
Mary F. Fernández (XML Query WG), AT&T Labs <mff@research.att.com>
Daniela Florescu (XML Query WG), BEA Systems <danielaf@bea.com>
Jonathan Robie (XML Query WG), DataDirect Technologies <jonathan.robie@datadirect-technologies.com>
Jérôme Siméon (XML Query WG), IBM T.J. Watson Research Center <simeon@us.ibm.com>

Abstract

XML is a versatile markup language, capable of labeling the information content of diverse data sources including structured and semi-structured documents, relational databases, and object repositories. A query language that uses the structure of XML intelligently can express queries across all these kinds of data, whether physically stored in XML or viewed as XML via middleware. This specification describes a query language called XQuery, which is designed to be broadly applicable across many types of XML data sources.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This is a public W3C Working Draft for review by W3C Members and other interested parties. Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

XQuery 1.0 has been defined jointly by the XML Query Working Group and the XSL Working Group (both part of the XML Activity). The XPath 2.0 and XQuery 1.0 Working Drafts are generated from a common source. These languages are closely related, sharing much of the same expression syntax and semantics, and much of the text found in the two Working Drafts is identical.

This working draft includes a number of changes made in response to comments received during the Last Call period that ended on Feb. 15, 2004. The working group is continuing to process these comments, and additional changes are expected. A list of changes introduced by this draft can be found in I Revision Log.

This document reflects decisions taken up to and including the face-to-face meeting in Cambridge, MA during the week of June 21, 2004. These decisions are recorded in the Last Call issues list (http://www.w3.org/2004/07/xquery-issues.html). However, some of these decisions may not yet have been made in this document.

Public comments on this document and its open issues are invited. Comments should be sent to the W3C XPath/XQuery mailing list, public-qt-comments@w3.org (archived at http://lists.w3.org/Archives/Public/public-qt-comments/), with “[XQuery]” at the beginning of the subject field.

The patent policy for this document is expected to become the 5 February 2004 W3C Patent Policy, pending the Advisory Committee review of the renewal of the XML Query Working Group. Patent disclosures relevant to this specification may be found on the XML Query Working Group's patent disclosure page and the XSL Working Group's patent disclosure page. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) with respect to this specification should disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1 Introduction
2 Basics
    2.1 Expression Context
        2.1.1 Static Context
        2.1.2 Dynamic Context
    2.2 Processing Model
        2.2.1 Data Model Generation
        2.2.2 Schema Import Processing
        2.2.3 Expression Processing
            2.2.3.1 Static Analysis Phase
            2.2.3.2 Dynamic Evaluation Phase
        2.2.4 Serialization
        2.2.5 Consistency Constraints
    2.3 Documents
        2.3.1 Document Order
        2.3.2 Atomization
        2.3.3 Effective Boolean Value
        2.3.4 Input Sources
    2.4 Types
        2.4.1 Predefined Types
        2.4.2 Typed Value and String Value
        2.4.3 SequenceType Syntax
        2.4.4 SequenceType Matching
            2.4.4.1 Matching a SequenceType and a Value
            2.4.4.2 Matching an ItemType and an Item
            2.4.4.3 Element Test
            2.4.4.4 Schema Element Test
            2.4.4.5 Attribute Test
            2.4.4.6 Schema Attribute Test
    2.5 Error Handling
        2.5.1 Kinds of Errors
        2.5.2 Handling Dynamic Errors
        2.5.3 Errors and Optimization
    2.6 Optional Features
        2.6.1 Schema Import Feature
        2.6.2 Static Typing Feature
        2.6.3 Full Axis Feature
        2.6.4 Module Feature
        2.6.5 Pragmas
        2.6.6 Must-Understand Extensions
            2.6.6.1 XQuery Flagger
        2.6.7 Static Typing Extensions
            2.6.7.1 XQuery Static Flagger
    2.7 Comments
3 Expressions
    3.1 Primary Expressions
        3.1.1 Literals
        3.1.2 Variable References
        3.1.3 Parenthesized Expressions
        3.1.4 Context Item Expression
        3.1.5 Function Calls
    3.2 Path Expressions
        3.2.1 Steps
            3.2.1.1 Axes
            3.2.1.2 Node Tests
        3.2.2 Predicates
        3.2.3 Unabbreviated Syntax
        3.2.4 Abbreviated Syntax
    3.3 Sequence Expressions
        3.3.1 Constructing Sequences
        3.3.2 Filter Expressions
        3.3.3 Combining Node Sequences
    3.4 Arithmetic Expressions
    3.5 Comparison Expressions
        3.5.1 Value Comparisons
        3.5.2 General Comparisons
        3.5.3 Node Comparisons
    3.6 Logical Expressions
    3.7 Constructors
        3.7.1 Direct Element Constructors
            3.7.1.1 Attributes
            3.7.1.2 Namespace Declaration Attributes
            3.7.1.3 Content
            3.7.1.4 Whitespace in Element Content
        3.7.2 Other Direct Constructors
        3.7.3 Computed Constructors
            3.7.3.1 Computed Element Constructors
            3.7.3.2 Computed Attribute Constructors
            3.7.3.3 Document Node Constructors
            3.7.3.4 Text Node Constructors
            3.7.3.5 Computed Processing Instruction Constructors
            3.7.3.6 Computed Comment Constructors
        3.7.4 In-scope Namespaces of a Constructed Element
    3.8 FLWOR Expressions
        3.8.1 For and Let Clauses
        3.8.2 Where Clause
        3.8.3 Order By and Return Clauses
        3.8.4 Example
    3.9 Ordered and Unordered Expressions
    3.10 Conditional Expressions
    3.11 Quantified Expressions
    3.12 Expressions on SequenceTypes
        3.12.1 Instance Of
        3.12.2 Typeswitch
        3.12.3 Cast
        3.12.4 Castable
        3.12.5 Constructor Functions
        3.12.6 Treat
    3.13 Validate Expressions
        3.13.1 Validating an Element Node
        3.13.2 Validating a Document Node
4 Modules and Prologs
    4.1 Version Declaration
    4.2 Module Declaration
    4.3 Xmlspace Declaration
    4.4 Default Collation Declaration
    4.5 Base URI Declaration
    4.6 Construction Declaration
    4.7 Default Namespace Declaration
    4.8 Default Ordering Declaration
    4.9 Schema Import
    4.10 Module Import
    4.11 Namespace Declaration
    4.12 Variable Declaration
    4.13 Function Declaration

Appendices

A XQuery Grammar
    A.1 EBNF
        A.1.1 Grammar Notes
    A.2 Lexical structure
        A.2.1 Terminal Types
        A.2.2 Whitespace Rules
            A.2.2.1 Default Whitespace Handling
            A.2.2.2 ExplicitSpecial Whitespace Handling
        A.2.3 Comments, Pragmas and Extensions
        A.2.4 Lexical Rules
    A.3 Reserved Function Names
    A.4 Precedence Order
B Type Promotion and Operator Mapping
    B.1 Type Promotion
    B.2 Operator Mapping
C Context Components
    C.1 Static Context Components
    C.2 Dynamic Context Components
    C.3 Serialization Parameters
D References
    D.1 Normative References
    D.2 Non-normative References
    D.3 Non-normative Background References
    D.4 Non-normative Informative Material
E Glossary
F Summary of Error Conditions (Non-Normative)
G Example Applications (Non-Normative)
    G.1 Joins
    G.2 Grouping
    G.3 Queries on Sequence
    G.4 Recursive Transformations
    G.5 Selecting Distinct Combinations
H XPath 2.0 and XQuery 1.0 Issues (Non-Normative)
I Revision Log (Non-Normative)
    I.1 23 July 2004


1 Introduction

As increasing amounts of information are stored, exchanged, and presented using XML, the ability to intelligently query XML data sources becomes increasingly important. One of the great strengths of XML is its flexibility in representing many different kinds of information from diverse sources. To exploit this flexibility, an XML query language must provide features for retrieving and interpreting information from these diverse sources.

XQuery is designed to meet the requirements identified by the W3C XML Query Working Group [XML Query 1.0 Requirements] and the use cases in [XML Query Use Cases]. It is designed to be a language in which queries are concise and easily understood. It is also flexible enough to query a broad spectrum of XML information sources, including both databases and documents. The Query Working Group has identified a requirement for both a human-readable query syntax and an XML-based query syntax. XQuery is designed to meet the first of these requirements. XQuery is derived from an XML query language called Quilt [Quilt], which in turn borrowed features from several other languages, including XPath 1.0 [XPath 1.0], XQL [XQL], XML-QL [XML-QL], SQL [SQL], and OQL [ODMG].

[Definition: XQuery operates on the abstract, logical structure of an XML document, rather than its surface syntax. This logical structure is known as the data model, which is defined in the [XQuery 1.0 and XPath 2.0 Data Model] document.]

XQuery Version 1.0 is an extension of XPath Version 2.0. Any expression that is syntactically valid and executes successfully in both XPath 2.0 and XQuery 1.0 will return the same result in both languages. Since these languages are so closely related, their grammars and language descriptions are generated from a common source to ensure consistency, and the editors of these specifications work together closely.

XQuery also depends on and is closely related to the following specifications:

This document specifies a grammar for XQuery, using the same Basic EBNF notation used in [XML 1.0]. Unless otherwise noted (see A.2 Lexical structure), whitespace is not significant in the grammar. Grammar productions are introduced together with the features that they describe, and a complete grammar is also presented in the appendix [A XQuery Grammar]. The appendix is the normative version.

In the grammar productions in this document, nonterminal symbols are underlined and literal text is enclosed in double quotes. Certain productions (including the productions that define DecimalLiteral, DoubleLiteral, and StringLiteral) employ a regular-expression notation. The following example production describes the syntax of a function call:

[83]    FunctionCall    ::=    QName "(" (ExprSingle ("," ExprSingle)*)? ")"

The production should be read as follows: A function call consists of a QName followed by an open-parenthesis. The open-parenthesis is followed by an optional argument list. The argument list (if present) consists of one or more expressions, separated by commas. The optional argument list is followed by a close-parenthesis.

Certain aspects of language processing are described in this specification as implementation-defined or implementation-dependent.

  • [Definition: Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementor for each particular implementation.]

  • [Definition: Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementor for any particular implementation.]

This document normatively defines the dynamic semantics of XQuery. The static semantics of XQuery are normatively defined in [XQuery 1.0 and XPath 2.0 Formal Semantics]. In this document, examples and material labeled as "Note" are provided for explanatory purposes and are not normative.

2 Basics

The basic building block of XQuery is the expression, which is a string of Unicode characters. This specification makes no assumptions or requirements regarding the character set encoding of strings of Unicode characters. The language provides several kinds of expressions which may be constructed from keywords, symbols, and operands. In general, the operands of an expression are other expressions. [Definition: XQuery is a functional language, which means that expressions can be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitutability if the variable declaration contains construction of new nodes.)] [Definition: XQuery is also a strongly-typed language in which the operands of various expressions, operators, and functions must conform to the expected types.]

Note:

This specification contains no assumptions or requirements regarding the character set encoding of strings of Unicode characters.

Like XML, XQuery is a case-sensitive language. Keywords in XQuery use lower-case characters and are not reserved—that is, names in XQuery expressions are allowed to be the same as language keywords—except for the list of reserved function-names in A.3 Reserved Function Names.

The value of an expression is always a sequence. [Definition: A sequence is an ordered collection of zero or more items.] [Definition: An item is either an atomic value or a node.] [Definition: An atomic value is a value in the value space of an atomic type, including all the atomic types defined in [XML Schema] and xdt:untypedAtomic.] [Definition: A node is an instance of one of the node kinds defined in [XQuery 1.0 and XPath 2.0 Data Model].] Each node has a unique node identity. Some kinds of nodes have typed values, string values, and names, which can be extracted from the node. The typed value of a node is a sequence of zero or more atomic values. The string value of a node is a value of type xs:string. The name of a node is a value of type xs:QName.

[Definition: A sequence containing exactly one item is called a singleton sequence.] An item is identical to a singleton sequence containing that item. Sequences are never nested—for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3). [Definition: A sequence containing zero items is called an empty sequence.]

Names in XQuery are called QNames, and conform to the syntax in [XML Names]. [Definition: Lexically, a QName consists of an optional namespace prefix and a local name.] A lexical QName can be converted into an expanded QName by resolving its namespace prefix, using algorithms described later in this document. [Definition: An expanded QName consists of an optional namespace URI and a local name.] Two QNames are considered equal if their namespace URIs are equal and their local names are equal (even if the prefixes in their lexical forms are not equal). Namespace URIs and local names are compared on a codepoint basis, without normalization.

This document uses the following predefined namespace prefixes:

  • xs = http://www.w3.org/2001/XMLSchema

  • xsi = http://www.w3.org/2001/XMLSchema-instance

  • fn = http://www.w3.org/2004/07/xpath-functions

  • xdt = http://www.w3.org/2004/07/xpath-datatypes

  • local = http://www.w3.org/2004/07/xquery-local-functions (see 4.13 Function Declaration.)

In some cases, where the meaning is clear and namespaces are not important to the discussion, built-in XML Schema typenames such as integer and string are used without a namespace prefix.

Element nodes have a property called in-scope namespaces. [Definition: The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI, thus defining the set of namespace prefixes that are available for interpreting QNames within the scope of the element. For a given element, one namespace binding may have an empty prefix; the URI of this namespace binding is the default namespace within the scope of the element.]

Note:

In [XPath 1.0], the in-scope namespaces of an element node are represented by a collection of namespace nodes arranged on a namespace axis, which is optional and deprecated in [XPath 2.0]. XQuery does not support the namespace axis and does not represent namespace bindings in the form of nodes. However, where other specifications such as [XSLT 2.0 and XQuery 1.0 Serialization] refer to namespace nodes, these nodes may be synthesized from the in-scope namespaces of an element node by interpreting each namespace binding as a namespace node.

2.1 Expression Context

[Definition: The expression context for a given expression consists of all the information that can affect the result of the expression.] This information is organized into two categories called the static context and the dynamic context.

2.1.1 Static Context

[Definition: The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.] This information can be used to decide whether the expression contains a static error. If analysis of an expression relies on some component of the static context that has not been assigned a value, a static error is raised.[err:XP0001]

The individual components of the static context are summarized below. Further rules governing the semantics of these components can be found in C.1 Static Context Components.

  • [Definition: XPath 1.0 compatibility mode. This component must be set by all host languages that include XPath 2.0 as a subset, indicating whether rules for compatibility with XPath 1.0 are in effect. XQuery sets the value of this component to false. ]

  • [Definition: Statically known namespaces. This is a set of (prefix, URI) pairs that define all the namespaces that are known during static processing of a given expression.] Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression.

    Some namespaces are predefined; additional namespaces can be added to the statically known namespaces by namespace declarations in a Prolog, by namespace declaration attributes in direct element constructors, and by local namespace declarations in computed element constructors.

  • [Definition: Default element/type namespace. This is a namespace URI or "none". The namespace URI, if present, is used for any unprefixed QName appearing in a position where an element or type name is expected.] The initial default element/type namespace may be provided by the external environmentor by a declaration in a Prolog.

  • [Definition: Default function namespace. This is a namespace URI that is used for any unprefixed QName appearing as the function name in a function call. The initial default function namespace may be provided by the external environmentor by a declaration in a Prolog.]

  • [Definition: In-scope schema definitions. This is a generic term for all the element, attribute, and type definitions that are in scope during processing of an expression.] It includes the following three parts:

    • [Definition: In-scope type definitions. Each named type definition is identified either by an expanded QName (for a named type) or by an implementation-dependent type identifier (for an anonymous type). The in-scope type definitions include the predefined types described in 2.4.1 Predefined Types. If the Schema Import Feature is supported, in-scope type definitions also include all type definitions found in imported schemas. ]

    • [Definition: In-scope element declarations. Each element declaration is identified either by an expanded QName (for a top-level element declaration) or by an implementation-dependent element identifier (for a local element declaration). If the Schema Import Feature is supported, in-scope element declarations include all element declarations found in imported schemas. ] An element declaration includes information about the element's substitution group affiliation.

      [Definition: Substitution groups are defined in [XML Schema] Part 1, Section 2.2.2.2. Informally, the substitution group headed by a given element (called the head element) consists of the set of elements that can be substituted for the head element without affecting the outcome of schema validation.]

    • [Definition: In-scope attribute declarations. Each attribute declaration is identified either by an expanded QName (for a top-level attribute declaration) or by an implementation-dependent attribute identifier (for a local attribute declaration). If the Schema Import Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.]

  • [Definition: In-scope variables. This is a set of (expanded QName, type) pairs. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.]

    Variable declarations in a Prolog are added to in-scope variables. An expression that binds a variable (such as a let, for, some, or every expression) extends the in-scope variables of its subexpressions with the new bound variable and its type. Within a function declaration, the in-scope variables are extended by the names and types of the function parameters.

    The static type of a variable may be either declared in a query or (if the Static Typing Feature is enabled) inferred by static type inference rules as described in [XQuery 1.0 and XPath 2.0 Formal Semantics].

  • Context item static type. This component defines the static type of the context item within the scope of a given expression.

  • [Definition: Function signatures. This component defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its expanded QName and its arity (number of parameters).] In addition to the name and arity, each function signature specifies the static types of the function parameters and result.

    The function signatures include the signatures of constructor functions, which are discussed in 3.12.5 Constructor Functions.

  • [Definition: Statically known collations. This is a set of (URI, collation) pairs. It defines the names of the collations that are available for use in function calls that take a collation name as an argument.] A collation may be regarded as an object that supports two functions: a function that given a set of strings, returns a sequence containing those strings in sorted order; and a function that given two strings, returns true if they are considered equal, and false if not.

  • [Definition: Default collation. This identifies one of the collations in statically known collations as the collation to be used by string comparison functions and operators when no explicit collation is specified.]

  • [Definition: Construction mode. The construction mode governs the behavior of element constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and the attributes and descendants of the constructed element retain their original types. If construction mode is strip, the type of the constructed element node and all its descendants is xdt:untyped, and attributes of the constructed element have type xdt:untypedAtomic.]

  • [Definition: Ordering mode. Ordering mode, which has the value ordered or unordered, affects the ordering of the result sequence returned by path expressions, union, intersect, and except expressions, and FLWOR expressions that have no order by clause.] Details are provided in the descriptions of these expressions.

  • [Definition: XMLSpace policy. This policy, declared in the Prolog, controls the processing of whitespace by element constructors.] Its value may be preserve or strip.

  • [Definition: Base URI. This is an absolute URI, used when necessary in the resolution of relative URIs (for example, by the fn:resolve-uri function.)]

  • [Definition: Statically known documents. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:doc function. The type is the static type of a call to fn:doc with the given URI as its literal argument. ] If the argument to fn:doc is not a string literal that is present in statically known documents, then the static type of fn:doc is document-node()?.

    Note:

    The purpose of the statically known documents is to provide static type information, not to determine which documents are available. A URI need not be found in the statically known documents to be accessed using fn:doc.

  • [Definition: Statically known collections. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:collection function. The type is the type of the sequence of nodes that would result from calling the fn:collection function with this URI as its argument.] If the argument to fn:collection is not a string literal that is present in statically known collections, then the static type of fn:collection is node()*.

    Note:

    The purpose of the statically known collections is to provide static type information, not to determine which collections are available. A URI need not be found in the statically known collections to be accessed using fn:collection.

  • XQuery Flagger status. This component has the value "on" if the XQuery Flagger is implemented and enabled; otherwise it has the value "off".

  • XQuery Static Flagger status. This component has the value "on" if the XQuery Static Flagger is implemented and enabled; otherwise it has the value "off".

2.1.2 Dynamic Context

[Definition: The dynamic context of an expression is defined as information that is available at the time the expression is evaluated.] If evaluation of an expression relies on some part of the dynamic context that has not been assigned a value, a dynamic error is raised.[err:XP0002]

The individual components of the dynamic context are summarized below. Further rules governing the semantics of these components can be found in C.2 Dynamic Context Components.

The dynamic context consists of all the components of the static context, and the additional components listed below.

[Definition: The first three components of the dynamic context (context item, context position, and context size) are called the focus of the expression. ] The focus enables the processor to keep track of which nodes are being processed by the expression.

Certain language constructs, notably the path expression E1/E2 and the filter expression E1[E2], create a new focus for the evaluation of a sub-expression. In these constructs, E2 is evaluated once for each item in the sequence that results from evaluating E1. Each time E2 is evaluated, it is evaluated with a different focus. The focus for evaluating E2 is referred to below as the inner focus, while the focus for evaluating E1 is referred to as the outer focus. The inner focus exists only while E2 is being evaluated. When this evaluation is complete, evaluation of the containing expression continues with its original focus unchanged.

  • [Definition: The context item is the item currently being processed. An item is either an atomic value or a node.][Definition: When the context item is a node, it can also be referred to as the context node.] The context item is returned by the expression ".". When an expression E1/E2 or E1[E2] is evaluated, each item in the sequence obtained by evaluating E1 becomes the context item in the inner focus for an evaluation of E2.

  • [Definition: The context position is the position of the context item within the sequence of items currently being processed.] It changes whenever the context item changes. Its value is always an integer greater than zero. The context position is returned by the expression fn:position(). When an expression E1/E2 or E1[E2] is evaluated, the context position in the inner focus for an evaluation of E2 is the position of the context item in the sequence obtained by evaluating E1. The position of the first item in a sequence is always 1 (one). The context position is always less than or equal to the context size.

  • [Definition: The context size is the number of items in the sequence of items currently being processed.] Its value is always an integer greater than zero. The context size is returned by the expression fn:last(). When an expression E1/E2 or E1[E2] is evaluated, the context size in the inner focus for an evaluation of E2 is the number of items in the sequence obtained by evaluating E1.

  • [Definition: Variable values. This is a set of (expanded QName, value) pairs. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The QName is the name of the variable and the value is the dynamic value of the variable.]

  • [Definition: Function implementations. Each function in function signatures has a function implementation that enables the function to map instances of its parameter types into an instance of its result type. For a user-defined function, the function implementation is an XQuery expression. For an external function, the function implementation is implementation-dependent.]

  • [Definition: Current date and time. This information represents an implementation-dependent point in time during processing of a query or transformation. It can be retrieved by the fn:current-date, fn:current-time, and fn:current-dateTime functions. If invoked multiple times during the execution of a query or transformation, these functions always return the same result.]

  • [Definition: Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or in any other operation. This value is an instance of xdt:dayTimeDuration that is implementation-defined . See [ISO 8601] for the range of legal values of a timezone.]

  • [Definition: Available documents. This is a mapping of strings onto document nodes. The string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc function when applied to that URI.] The set of available documents is not constrained by the set of statically known documents, and it may be empty.

  • [Definition: Available collections. This is a mapping of strings onto sequences of nodes. The string represents the absolute URI of a resource. The sequence of nodes represents the result of the fn:collection function when that URI is supplied as the argument. ] The set of available collections is not constrained by the set of statically known collections, and it may be empty.

2.2 Processing Model

XQuery is defined in terms of the data model and in terms of the expression context.

Processing Model Overview

Figure 1: Processing Model Overview

Figure 1 provides a schematic overview of the processing steps that are discussed in detail below. Some of these steps are completely outside the domain of XQuery; in Figure 1, these are depicted outside the line that represents the boundaries of the language, an area labeled the external processing domain. The external processing domain includes generation of the data model (see 2.2.1 Data Model Generation), schema import processing (see 2.2.2 Schema Import Processing) and serialization (see 2.2.4 Serialization). The area inside the boundaries of the language is known as the query processing domain, which includes the static analysis and dynamic evaluation phases (see 2.2.3 Expression Processing). Consistency constraints on the query processing domain are defined in 2.2.5 Consistency Constraints.

2.2.1 Data Model Generation

Before an expression can be processed, the input documents to be accessed by the expression must be represented in the data model. This process occurs outside the domain of XQuery, which is why Figure 1 represents it in the external processing domain. Here are some steps by which an XML document might be converted to the data model:

  1. A document may be parsed using an XML parser that generates an XML Information Set (see [XML Infoset]). The parsed document may then be validated against one or more schemas. This process, which is described in [XML Schema], results in an abstract information structure called the Post-Schema Validation Infoset (PSVI). If a document has no associated schema, its Information Set is preserved. (See DM1 in Fig. 1.)

  2. The Information Set or PSVI may be transformed into the data model by a process described in [XQuery 1.0 and XPath 2.0 Data Model]. (See DM2 in Fig. 1.)

The above steps provide an example of how a document in the data model might be constructed. A document or fragment might also be synthesized directly from a relational database, or constructed in some other way (see DM3 in Fig. 1.) XQuery is defined in terms of operations on the data model, but it does not place any constraints on how documents and instances in the data model are constructed.

Each atomic value, element node, and attribute node in the data model is annotated with its dynamic type. The dynamic type specifies a range of values—for example, an attribute named version might have the dynamic type xs:decimal, indicating that it contains a decimal value. For example, if the data model was derived from an input XML document, the dynamic types of the elements and attributes are derived from schema validation.

The value of an attribute is represented directly within the attribute node. An attribute node whose type is unknown (such as might occur in a schemaless document) is annotated with the dynamic type xdt:untypedAtomic.

The value of an element is represented by the children of the element node, which may include text nodes and other element nodes. The dynamic type of an element node indicates how the values in its child text nodes are to be interpreted. An element that has not been validated (such as might occur in a schemaless document) is annotated with the type xdt:untyped. An element that has been validated and found to be partially valid is annotated with the type xs:anyType. If an element node is annotated xdt:untyped, all its descendant element nodes are also annotated xdt:untyped. However, if an element node is annotated xs:anyType, some of its descendant element nodes may have a more specific type annotation.

An atomic value of unknown type is annotated with the type xdt:untypedAtomic.

2.2.2 Schema Import Processing

The in-scope schema definitions in the static context may be extracted from actual XML Schemata as described in [XQuery 1.0 and XPath 2.0 Formal Semantics] (see step SI1 in Figure 1) or may be generated by some other mechanism (see step SI2 in Figure 1). In either case, the result must satisfy the consistency constraints defined in 2.2.5 Consistency Constraints.

2.2.3 Expression Processing

XQuery defines two phases of processing called the static analysis phase and the dynamic evaluation phase (see Fig. 1). An implementation is free to use any strategy or algorithm whose result conforms to these specifications.

2.2.3.1 Static Analysis Phase

[Definition: The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).]

During the static analysis phase, the query is parsed into an internal representation called the operation tree (step SQ1 in Figure 1). A parse error is raised as a static error.[err:XP0003] The static context is initialized by the implementation (step SQ2). The static context is then changed and augmented based on information in the prolog (step SQ3). If the Schema Import Feature is supported, the in-scope schema definitions are populated with information from imported schemata. The static context is used to resolve type names, function names, namespace prefixes and variable names (step SQ4). If a name in the operation tree is not found in the static context, a static error [err:XP0008] is raised (however, see exceptions to this rule in 2.4.4.3 Element Test and 2.4.4.5 Attribute Test.

The operation tree is then normalized by making explicit the implicit operations such as atomization, type promotion, and extraction of Effective Boolean Values (step SQ5). The normalization process is described in [XQuery 1.0 and XPath 2.0 Formal Semantics].

If the Static Typing Feature is supported, each expression is assigned a static type (step SQ6). [Definition: The static type of an expression may be either a named type or a structural description—for example, xs:boolean? denotes an optional occurrence of the xs:boolean type. The rules for inferring the static types of various expressions are described in [XQuery 1.0 and XPath 2.0 Formal Semantics].] In some cases, the static type is derived from the lexical form of the expression; for example, the static type of the literal 5 is xs:integer. In other cases, the static type of an expression is inferred according to rules based on the static types of its operands; for example, the static type of the expression 5 + 1.2 is xs:decimal.

During the static analysis phase, if the Static Typing Feature is in effect and an operand of an expression is found to have a static type that is not appropriate for that operand, a type error is raised.[err:XP0004] If static type checking raises no errors and assigns a static type T to an expression, then execution of the expression on valid input data is guaranteed either to produce a value of type T or to raise a dynamic error.

During the static analysis phase, if the Static Typing Feature is in effect and the static type assigned to an expression other than () or data(()) is empty(), a static error is raised.[err:XP0005] This catches cases in which a query refers to an element or attribute that is not present in the in-scope schema definitions, possibly because of a spelling error.

The purpose of type-checking during the static analysis phase is to provide early detection of type errors and to infer type information that may be useful in optimizing the evaluation of an expression.

2.2.3.2 Dynamic Evaluation Phase

[Definition: The dynamic evaluation phase occurs after completion of the static analysis phase. During the dynamic evaluation phase, the value of the query is computed.]

The dynamic evaluation phase can occur only if no errors were detected during the static analysis phase. If the Static Typing Feature is in effect, all type errors are detected during static analysis and serve to inhibit the dynamic evaluation phase. If the Static Typing Feature is not in effect, an implementation is allowed to raise type-related warnings during the static analysis phase. It may then proceed with the dynamic evaluation phase; in this case, type errors must be detected and raised during dynamic evaluation.

The dynamic evaluation phase depends on the operation tree of the expression being evaluated (step DQ1), on the input data (step DQ4), and on the dynamic context (step DQ5), which in turn draws information from the external environment (step DQ3) and the static context (step DQ2). Execution of the evaluation phase may create new data-model values (step DQ4) and it may extend the dynamic context (step DQ5)—for example, by binding values to variables.

[Definition: A dynamic type is associated with each value as it is computed. The dynamic type of a value may be either a structural description (such as "sequence of integers") or a named type.] The dynamic type of a value may be more specific than the static type of the expression that computed it (for example, the static type of an expression might be "zero or more integers or strings," but at evaluation time its value may have the dynamic type "integer.")

If an operand of an expression is found to have a dynamic type that is not appropriate for that operand, a type error is raised.[err:XP0006]

Even though static typing can catch many type errors before an expression is executed, it is possible for an expression to raise an error during evaluation that was not detected by static analysis. For example, an expression may contain a cast of a string into an integer, which is statically valid. However, if the actual value of the string at run time cannot be cast into an integer, a dynamic error will result. Similarly, an expression may apply an arithmetic operator to a value whose static type is xdt:untypedAtomic. This is not a static error, but at run time, if the value cannot be successfully cast to a numeric type, a dynamic error will be raised.

When the Static Typing Feature is in effect, it is also possible for static analysis of an expression to raise a type error, even though execution of the expression on certain inputs would be successful. For example, an expression might contain a function that requires an element as its parameter, and the static analysis phase might infer the static type of the function parameter to be an optional element. This case is treated as a type error and inhibits evaluation, even though the function call would have been successful for input data in which the optional element is present.

2.2.4 Serialization

[Definition: Serialization is the process of converting a sequence of nodes and atomic values from the data model into a sequence of octets (step DM4 in Figure 1.) ] The general framework for serialization of the data model is described in [XSLT 2.0 and XQuery 1.0 Serialization].

An XQuery implementation is not required to provide a serialization interface. For example, an implementation may only provide a DOM interface or an interface based on an event stream. In these cases, serialization would be outside of the scope of this specification.

[XSLT 2.0 and XQuery 1.0 Serialization] defines a set of serialization parameters that govern the serialization process. If an XQuery implementation provides a serialization interface, it may support (and may expose to users) any of the serialization parameters listed (with default values) in C.3 Serialization Parameters. An XQuery implementation that provides a serialization interface must support some combination of serialization parameters in which method = "xml" and version = "1.0".

2.2.5 Consistency Constraints

In order for XQuery to be well defined, the data model, the static context, and the dynamic context must be mutually consistent. The consistency constraints listed below are prerequisites for correct functioning of an XQuery implementation. Enforcement of these consistency constraints is beyond the scope of this specification. This specification does not define the result of a query under any condition in which one or more of these constraints is not satisfied.

Some of the consistency constraints use the term data model schema. [Definition: For a given node in the data model, the data model schema is defined as the schema from which the type annotation of that node was derived.] For a node that was constructed by some process other than schema validation, the data model schema consists simply of the type definition that is represented by the type annotation of the node.

  • For every data model node that has a type annotation, if that type annotation is found in the in-scope schema definitions (ISSD), then its definition in the ISSD must be the same as its definition in the data model schema. Furthermore, all types that are derived by extension from the given type in the data model schema must also be known by equivalent definitions in the ISSD.

  • For every element name EN that is found both in a data model node and in the in-scope schema definitions (ISSD), all elements that are known in the data model schema to be in the substitution group headed by EN must also be known in the ISSD to be in the substitution group headed by EN.

  • Every item type (i.e., every element, attribute, or type name) referenced in in-scope variables or function signatures must be in the in-scope schema definitions.

  • For each mapping of a string to a document node in available documents, if there exists a mapping of the same string to a document type in statically known documents, the document node must match the document type, using the matching rules in 2.4.4 SequenceType Matching.

  • For each mapping of a string to a sequence of nodes in available collections, if there exists a mapping of the same string to a type in statically known collections, the sequence of nodes must match the type, using the matching rules in 2.4.4 SequenceType Matching.

  • For each (variable, type) pair in in-scope variables and the corresponding (variable, value) pair in variable values such that the variable names are equal, the value must match the type, using the matching rules in 2.4.4 SequenceType Matching.

  • For each variable declared as external: If the variable declaration includes a declared type, the external environment must provide a value for the variable that matches the declared type, using the matching rules in 2.4.4 SequenceType Matching. If the variable declaration does not include a declared type, the external environment must provide a type and a matching value, using the same matching rules.

  • For a given query, define a participating ISSD as the in-scope schema definitions of a module that is used in evaluating the query. If two participating ISSDs contain a definition for the same type name, element name, or attribute name, the definitions must be equivalent in both ISSDs. Furthermore, if two participating ISSDs each contain a definition of a type name T, the set of types derived by extension from T must be equivalent in both ISSDs. Also, if two participating ISSDs each contain a definition of an element name E, the substitution group headed by E must be equivalent in both ISSDs.

2.3 Documents

XQuery is generally used to process documents. The representation of a document is normatively defined in [XQuery 1.0 and XPath 2.0 Data Model]. The functions used to access documents and collections are normatively defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. Because documents are centrally important in XQuery processing, we provide a summary of some key concepts here.

2.3.1 Document Order

An ordering called document order is defined among all the nodes used during a given query or transformation, which may consist of one or more trees (documents or fragments). Document order is defined in [XQuery 1.0 and XPath 2.0 Data Model], and its definition is repeated here for convenience. [Definition: The node ordering that is the reverse of document order is called reverse document order.]

Document order is a total ordering, although the relative order of some nodes is implementation-dependent. [Definition: Informally, document order is the order defined by a pre-order, depth-first traversal of the nodes in the data model.] Document order is stable, which means that the relative order of two nodes will not change during the processing of a given query or transformation, even if this order is implementation-dependent.

Within a tree, document order satisfies the following constraints:

  1. The root node is the first node.

  2. The relative order of siblings is determined by their order in the XML representation of the tree. A node N1 occurs before a node N2 in document order if and only if the start of N1 occurs before the start of N2 in the XML representation.

  3. Attribute nodes immediately follow the element node with which they are associated. The relative order of attribute nodes is stable but implementation-dependent.

  4. Element nodes occur before their children; children occur before following-siblings.

The relative order of nodes in distinct trees is stable but implementation-dependent, subject to the following constraint: If any node in tree T1 is before any node in tree T2, then all nodes in tree T1 are before all nodes in tree T2.

2.3.2 Atomization

The semantics of some XQuery operators depend on a process called atomization. [Definition: Atomization is applied to a value when the value is used in a context in which a sequence of atomic values is required. The result of atomization is either a sequence of atomic values or a type error. Atomization of a sequence is defined as the result of invoking the fn:data function on the sequence, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].]

The semantics of fn:data are repeated here for convenience. The result of fn:data is the sequence of atomic values produced by applying the following rules to each item in the input sequence:

  • If the item is an atomic value, it is returned.

  • If the item is a node, its typed value is returned.

Atomization is used in processing the following types of expressions:

  • Arithmetic expressions

  • Comparison expressions

  • Function calls and returns

  • Cast expressions

  • Computed element and attribute constructors.

2.3.3 Effective Boolean Value

Under certain circumstances (listed below), it is necessary to find the effective boolean value of a value. [Definition: The effective boolean value of a value is defined as the result of applying the fn:boolean function to the value, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].]

The semantics of fn:boolean are repeated here for convenience. fn:boolean returns false if its operand is any of the following:

  • An empty sequence

  • The boolean value false

  • A zero-length value of type xs:string or xdt:untypedAtomic

  • A numeric value that is equal to zero

  • The xs:double or xs:float value NaN

Otherwise, fn:boolean returns true.

The effective boolean value of a sequence is computed implicitly during processing of the following types of expressions:

  • Logical expressions (and, or)

  • The fn:not function

  • The where clause of a FLWOR expression

  • Certain types of predicates, such as a[b]

  • Conditional expressions (if)

  • Quantified expressions (some, every)

Note:

Note that the definition of effective boolean value is not used when casting a value to the type xs:boolean.

2.3.4 Input Sources

XQuery has a set of functions that provide access to input data. These functions are of particular importance because they provide a way in which an expression can reference a document or a collection of documents. The input functions are described informally here; they are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].

An expression can access input data either by calling one of the input functions or by referencing some part of the expression context that is initialized by the external environment, such as a variable or a context item.

The input functions supported by XQuery are as follows:

  • The fn:doc function takes a string containing a URI that refers to an XML document, and returns a document node whose content is the data model representation of the given document.

  • The fn:collection function takes a string containing a URI, and returns the data model representation of the collection identified by the URI. A collection may be any sequence of nodes. For example, the expression fn:collection("http://example.org")//customer identifies all the customer elements that are descendants of nodes found in the collection whose URI is http://example.org.

If a given input function is invoked repeatedly with arguments that resolve to the same absolute URI during the scope of a single query or transformation, each invocation returns the same result.

2.4 Types

XQuery is a strongly typed language with a type system based on [XML Schema]. The XQuery type system is formally defined in [XQuery 1.0 and XPath 2.0 Formal Semantics].

2.4.1 Predefined Types

The in-scope type definitions in the static context are initialized with certain predefined types, including the built-in types of [XML Schema]. These built-in types are in the namespace http://www.w3.org/2001/XMLSchema, which has the predefined namespace prefix xs. Some examples of built-in schema types include xs:integer, xs:string, and xs:date. Element and attribute declarations in the xs namespace are not implicitly included in the static context.

In addition, the predefined types of XQuery include the types defined in the namespace http://www.w3.org/2004/07/xpath-datatypes, which has the predefined namespace prefix xdt. The types in this namespace are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators] and are summarized below.

  1. [Definition: xdt:untyped is used to denote the dynamic type of an element node that has not been validated, or has been validated in skip mode.] It has no subtypes.

  2. [Definition: xdt:untypedAtomic is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] It has no subtypes. An attribute that has been validated in skip mode, or that has a PSVI property of xs:anySimpleType, is represented in the Data Model by an attribute node with the type xdt:untypedAtomic.

  3. [Definition: xdt:dayTimeDuration is a subtype of xs:duration whose lexical representation is restricted to contain only day, hour, minute, and second components.]

  4. [Definition: xdt:yearMonthDuration is a subtype of xs:duration whose lexical representation is restricted to contain only year and month components.]

  5. [Definition: xdt:anyAtomicType includes all atomic values (and no values that are not atomic).] It is a subtype of xs:anySimpleType, which is the base type for all simple types, including atomic, list, and union types. All specific atomic types such as xs:integer, xs:string, and xdt:untypedAtomic, are subtypes of xdt:anyAtomicType.

    Note:

    xdt:anyAtomicType will not appear as the type of an actual value in the Data Model.

The relationships among the types in the xs and xdt namespaces are illustrated in Figure 2. A more complete description of the XQuery type hierarchy can be found in [XQuery 1.0 and XPath 2.0 Functions and Operators].

Type Hierarchy Diagram

Figure 2: Summary of XQuery Type Hierarchy

2.4.2 Typed Value and String Value

In the data model, every node has a typed value and a string value. The typed value of a node is a sequence of atomic values and can be extracted by applying the fn:data function to the node. The typed value for each kind of node is defined by the dm:typed-value accessor in [XQuery 1.0 and XPath 2.0 Data Model]. The string value of a node is a string and can be extracted by applying the fn:string function to the node. The string value for each kind of node is defined by the dm:string-value accessor in [XQuery 1.0 and XPath 2.0 Data Model]. Element and attribute nodes have a type annotation, which represents (in an implementation-dependent way) the dynamic (run-time) type of the node. In the [XQuery 1.0 and XPath 2.0 Data Model], type annotation is defined by the dm:type-name accessor; however, XQuery does not provide a way to directly access the type annotation of an element or attribute node.

The relationship between the typed value and the string value for various kinds of nodes is described and illustrated by examples below.

  1. For text and document nodes, the typed value of the node is the same as its string value, as an instance of the type xdt:untypedAtomic. (The string value of a document node is formed by concatenating the string values of all its descendant text nodes, in document order.)

  2. The typed value of a comment or processing instruction node is the same as its string value. It is an instance of the type xs:string.

  3. The typed value of an attribute node with the type annotation xdt:untypedAtomic is the same as its string value, as an instance of xdt:untypedAtomic. The typed value of an attribute node with any other type annotation is derived from its string value and type annotation using the lexical-to-value-space mapping defined in [XML Schema] Part 2 for the relevant type.

    Example: A1 is an attribute having string value "3.14E-2" and type annotation xs:double. The typed value of A1 is the xs:double value whose lexical representation is 3.14E-2.

    Example: A2 is an attribute with type annotation xs:IDREFS, which is a list datatype derived from the atomic datatype xs:IDREF. Its string value is "bar baz faz". The typed value of A2 is a sequence of three atomic values ("bar", "baz", "faz"), each of type xs:IDREF. The typed value of a node is never treated as an instance of a named list type. Instead, if the type annotation of a node is a list type (such as xs:IDREFS), its typed value is treated as a sequence of the atomic type from which it is derived (such as xs:IDREF).

  4. For an element node, the relationship between typed value and string value depends on the node's type annotation, as follows:

    1. If the type annotation is xdt:untyped or denotes a complex type with mixed content (including xs:anyType), then the typed value of the node is equal to its string value, as an instance of xdt:untypedAtomic.

      Example: E1 is an element node having type annotation xdt:untyped and string value "1999-05-31". The typed value of E1 is "1999-05-31", as an instance of xdt:untypedAtomic.

      Example: E2 is an element node with the type annotation formula, which is a complex type with mixed content. The content of E2 consists of the character "H", a child element named subscript with string value "2", and the character "O". The typed value of E2 is "H2O" as an instance of xdt:untypedAtomic.

    2. If the type annotation denotes a simple type or a complex type with simple content, then the typed value of the node is derived from its string value and its type annotation in a way that is consistent with schema validation.

      Example: E3 is an element node with the type annotation cost, which is a complex type that has several attributes and a simple content type of xs:decimal. The string value of E3 is "74.95". The typed value of E3 is 74.95, as an instance of xs:decimal.

      Example: E4 is an element node with the type annotation hatsizelist, which is a simple type derived from the atomic type hatsize, which in turn is derived from xs:integer. The string value of E4 is "7 8 9". The typed value of E4 is a sequence of three values (7, 8, 9), each of type hatsize.

    3. If the type annotation denotes a complex type with empty content, then the typed value of the node is the empty sequence and its string value is the zero-length string.

    4. If the type annotation denotes a complex type with element-only content, then the typed value of the node is undefined. The fn:data function raises a type error [err:XP0007] when applied to such a node.

      Example: E5 is an element node with the type annotation weather, which is a complex type whose content type specifies element-only. E5 has two child elements named temperature and precipitation. The typed value of E5 is undefined, and the fn:data function applied to E5 raises an error.

2.4.3 SequenceType Syntax

[Definition: When it is necessary to refer to a type in an XQuery expression, the SequenceType syntax is used. The name SequenceType suggests that this syntax is used to describe the type of an XQuery value, which is always a sequence.]

[110]    SequenceType    ::=    (ItemType OccurrenceIndicator?)
| ("empty" "(" ")")
[112]    ItemType    ::=    AtomicType | KindTest | ("item" "(" ")")
[111]    OccurrenceIndicator    ::=    "?" | "*" | "+"
[113]    AtomicType    ::=    QName
[114]    KindTest    ::=    DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| AnyKindTest
[116]    DocumentTest    ::=    "document-node" "(" (ElementTest | SchemaElementTest)? ")"
[124]    ElementTest    ::=    "element" "(" (ElementNameOrWildcard ("," TypeName "?"?)?)? ")"
[126]    SchemaElementTest    ::=    "schema-element" "(" ElementDeclaration ")"
[127]    ElementDeclaration    ::=    ElementName
[120]    AttributeTest    ::=    "attribute" "(" (AttribNameOrWildcard ("," TypeName)?)? ")"
[122]    SchemaAttributeTest    ::=    "schema-attribute" "(" AttributeDeclaration ")"
[123]    AttributeDeclaration    ::=    AttributeName
[125]    ElementNameOrWildcard    ::=    ElementName | "*"
[129]    ElementName    ::=    QName
[121]    AttribNameOrWildcard    ::=    AttributeName | "*"
[128]    AttributeName    ::=    QName
[130]    TypeName    ::=    QName
[119]    PITest    ::=    "processing-instruction" "(" (NCName | StringLiteral)? ")"
[118]    CommentTest    ::=    "comment" "(" ")"
[117]    TextTest    ::=    "text" "(" ")"
[115]    AnyKindTest    ::=    "node" "(" ")"

Here are some examples of SequenceTypes that might be used in XQuery expressions:

  • xs:date refers to the built-in atomic Schema type named xs:date

  • attribute()? refers to an optional attribute

  • element() refers to any element

  • element(po:shipto, po:address) refers to an element that has the name po:shipto and has the type annotation po:address (or a type derived from po:address)

  • element(*, po:address) refers to an element of any name that has the type annotation po:address (or a type derived from po:address)

  • element(customer) refers to an element named customer of any type

  • schema-element(customer) refers to an element named customer whose type annotation matches the type declared for a customer element in the in-scope element declarations

  • node()* refers to a sequence of zero or more nodes of any type

  • item()+ refers to a sequence of one or more nodes or atomic values

2.4.4 SequenceType Matching

[Definition: During evaluation of an expression, it is sometimes necessary to determine whether a value with a known type "matches" an expected type, expressed in the SequenceType syntax. This process is known as SequenceType matching.] For example, an instance of expression returns true if the actual type of a given value matches a given type, or false if it does not.

Note:

In this specification, the word "type", when used without modification, represents a type that can be expressed using the SequenceType syntax. When we refer specifically to XML Schema simple or complex types, appropriate modifiers are used to make this clear.

QNames appearing in a SequenceType have their prefixes expanded to namespace URIs by means of the statically known namespaces and the default element/type namespace. As usual, two QNames are considered to be equal if their local parts are the same and their namespace URI's are the same.

[Definition: The use of a value whose actual type is derived from the expected type is known as subtype substitution.] Subtype substitution does not change the actual type of a value. For example, if an xs:integer value is used where an xs:decimal value is expected, the value retains its type as xs:integer.

The rules for SequenceType matching compare the actual type of a value with an expected type. These rules are a subset of the formal rules that match a value with an expected type defined in [XQuery 1.0 and XPath 2.0 Formal Semantics], because the Formal Semantics must be able to match a value with any XML Schema type, whereas the rules below only match values against those types expressible by the SequenceType syntax.

Some of the rules for SequenceType matching require determining whether a given type name is the same as or derived from an expected type name. The given type name may be "known" (defined in the in-scope schema definitions), or "unknown" (not defined in the in-scope schema definitions). An unknown type name might be encountered, for example, if a source document has been validated using a schema that was not imported into the static context. In this case, an implementation is allowed (but is not required) to provide an implementation-dependent mechanism for determining whether the unknown type name is derived from the expected type name. For example, an implementation might maintain a data dictionary containing information about type hierarchies.

The definition of SequenceType matching relies on a pseudo-function named derives-from(AT, ET), which takes an an actual simple or complex type name AT and an expected simple or complex type name ET, and either returns a boolean value or raises a type error. [err:XP0004][err:XP0006] The pseudo-function derives-from is defined below and is defined formally in [XQuery 1.0 and XPath 2.0 Formal Semantics].

  • derives-from(AT, ET) returns true if any of the following three conditions is true:

    1. AT is a type name found in the in-scope schema definitions, and is the same as ET or is derived by restriction or extension from ET

    2. AT is a type name not found in the in-scope schema definitions, and an implementation-dependent mechanism is able to determine that AT is derived by restriction from ET

    3. There exists some type name IT such that derives-from(IT, ET) and derives-from(AT, IT) are true.

  • derives-from(AT, ET) returns false if either the first and third or the second and third of the following conditions are true:

    1. AT is a type name found in the in-scope schema definitions, and is not the same as ET, and is not is derived by restriction or extension from ET

    2. AT is a type name not found in the in-scope schema definitions, and an implementation-dependent mechanism is able to determine that AT is not derived by restriction from ET

    3. No type name IT exists such that derives-from(IT, ET) and derives-from(AT, IT) are true.

  • derives-from(AT, ET) raises a type error [err:XP0004][err:XP0006] if:

    1. ET is an unknown type, or

    2. AT is an unknown type, and the implementation is not able to determine whether AT is derived by restriction from ET.

Note:

The derives-from pseudo-function cannot be written as a real XQuery function, because types are not valid function parameters.

The rules for SequenceType matching are given below, with examples (the examples are for purposes of illustration, and do not cover all possible cases).

2.4.4.1 Matching a SequenceType and a Value

An OccurrenceIndicator specifies the number of items in a sequence, as follows:

  • ? matches zero or one items

  • * matches zero or more items

  • + matches one or more items

As a consequence of these rules, any SequenceType whose OccurrenceIndicator is * or ? matches a value that is an empty sequence.

2.4.4.2 Matching an ItemType and an Item
  • An ItemType consisting simply of a QName is interpreted as an AtomicType. An AtomicType AtomicType matches an atomic value whose actual type is AT if derives-from(AT, AtomicType) is true. If a QName that is used as an AtomicType is not defined as an atomic type in the in-scope type definitions, a static error is raised. [err:XP0051]

    Example: The AtomicType xs:decimal matches the value 12.34 (a decimal literal). xs:decimal also matches a value whose type is shoesize, if shoesize is an atomic type derived by restriction from xs:decimal.

    Note:

    The names of non-atomic types such as xs:IDREFS are not accepted in this context, but can often be replaced by an atomic type with an occurrence indicator, such as xs:IDREF*.

  • item() matches any single item.

    Example: item() matches the atomic value 1 or the element <a/>.

  • node() matches any node.

  • text() matches any text node.

  • processing-instruction() matches any processing-instruction node.

  • processing-instruction(N) matches any processing-instruction node whose name (called its "PITarget" in XML) is equal to N, where N is an NCName.

    Example: processing-instruction(xml-stylesheet) matches any processing instruction whose PITarget is xml-stylesheet.

    For backward compatibility with XPath 1.0, the PITarget of a processing instruction may also be expressed as a string literal, as in this example: processing-instruction("xml-stylesheet").

  • comment() matches any comment node.

  • document-node() matches any document node.

  • document-node(E) matches any document node that contains exactly one element node, optionally accompanied by one or more comment and processing instruction nodes, if E is an ElementTest or SchemaElementTest that matches the element node (see 2.4.4.3 Element Test and 2.4.4.4 Schema Element Test).

    Example: document-node(element(book)) matches a document node containing exactly one element node that is matched by the ElementTest element(book).

  • An ItemType that is an ElementTest, SchemaElementTest, AttributeTest, or SchemaAttributeTest matches an element or attribute node as described in the following sections.

2.4.4.3 Element Test

An ElementTest is used to match an element node by its name and/or type. An ElementTest any take any of the following forms. In these forms, ElementName and TypeName may be any QNames, and need not be present in the in-scope schema definitions. Note that substitution groups do not affect the semantics of ElementTest.

  1. element() and element(*) match any single element node, regardless of its name or type.

  2. element(ElementName) matches any element node whose name is ElementName, regardless of its type or nilled property.

    Example: element(person) matches any element node whose name is person.

  3. element(ElementName, TypeName) matches an element node whose name is ElementName if derives-from(AT, TypeName ) is true, where AT is the type of the element node, and the nilled property of the node is false.

    Example: element(person, surgeon) matches a non-nilled element node whose name is person and whose type annotation is surgeon.

  4. element(ElementName, TypeName ?) matches an element node whose name is ElementName if derives-from(AT, TypeName) is true, where AT is the type of the element node. The nilled property of the node may be either true or false.

    Example: element(person, surgeon?) matches a nilled or non-nilled element node whose name is person and whose type annotation is surgeon.

  5. element(*, TypeName) matches an element node regardless of its name, if derives-from(AT, TypeName ) is true, where AT is the type of the element node, and the nilled property of the node is false.

    Example: element(*, surgeon) matches any non-nilled element node whose type annotation is surgeon, regardless of its name.

  6. element(*, TypeName ?) matches an element node regardless of its name, if derives-from(AT, TypeName ) is true, where AT is the type of the element node. The nilled property of the node may be either true or false.

    Example: element(*, surgeon?) matches any nilled or non-nilled element node whose type annotation is surgeon, regardless of its name.

2.4.4.4 Schema Element Test

A SchemaElementTest matches an element node against a corresponding element declaration found in the in-scope element declarations. It takes the following form:

schema-element(ElementName)

If the ElementName specified in the SchemaElementTest is not found in the in-scope element declarations, a static error is raised. [err:XP0008]

A SchemaElementTest matches a candidate element node if all three of the following conditions are satisfied:

  1. The name of the candidate node matches the specified ElementName or matches the name of an element in a substitution group headed by an element named ElementName.

  2. derives-from(AT, ET) is true, where AT is the type of the candidate node and ET is the type declared for element ElementName in the in-scope element declarations.

  3. Either the nilled property of the candidate node is false, or the element declaration for ElementName in the in-scope element declarations is nillable.

Example: The SchemaElementTest schema-element(customer) matches a candidate element node if customer is a top-level element declaration in the in-scope element declarations, the name of the candidate node is customer or is in a substitution group headed by customer, the type of the candidate node is the same as or derived from the type declared for the customer element, and either the candidate node is not nilled or customer is declared to be nillable.

2.4.4.5 Attribute Test

An AttributeTest is used to match an attribute node by its name and/or type. An AttributeTest any take any of the following forms. In these forms, AttributeName and TypeName may be any QNames, and need not be present in the in-scope schema definitions.

  1. attribute() and attribute(*) match any single attribute node, regardless of its name or type.

  2. attribute(AttributeName) matches any attribute node whose name is AttributeName, regardless of its type or nilled property.

    Example: attribute(price) matches any attribute node whose name is price.

  3. attribute(AttributeName, TypeName) matches an attribute node whose name is AttributeName if derives-from(AT, TypeName ) is true, where AT is the type of the attribute node.

    Example: attribute(price, currency) matches an attribute node whose name is price and whose type annotation is currency.

  4. attribute(*, TypeName) matches an attribute node regardless of its name, if derives-from(AT, TypeName) is true, where AT is the type of the attribute node.

    Example: attribute(*, currency) matches any attribute node whose type annotation is currency, regardless of its name.

2.4.4.6 Schema Attribute Test

A SchemaAttributeTest matches an attribute node against a corresponding attribute declaration found in the in-scope attribute declarations. It takes the following form:

schema-attribute(AttributeName)

If the AttributeName specified in the SchemaAttributeTest is not found in the in-scope attribute declarations, a static error is raised. [err:XP0008]

A SchemaAttributeTest matches a candidate attribute node if both of the following conditions are satisfied:

  1. The name of the candidate node matches the specified AttributeName.

  2. derives-from(AT, ET) is true, where AT is the type of the candidate node and ET is the type declared for attribute AttributeName in the in-scope attribute declarations.

Example: The SchemaAttributeTest schema-attribute(color) matches a candidate attribute node if color is a top-level attribute declaration in the in-scope attribute declarations, the name of the candidate node is color, and the type of the candidate node is the same as or derived from the type declared for the color attribute.

2.5 Error Handling

2.5.1 Kinds of Errors

As described in 2.2.3 Expression Processing, XQuery defines an analysis phase, which does not depend on input data, and an evaluation phase, which does depend on input data. Errors may be raised during each phase.

[Definition: A static error is an error that must be detected during the analysis phase. A syntax error is an example of a static error. The means by which static errors are reported during the analysis phase is implementation-defined. ]

[Definition: A dynamic error is an error that must be detected during the evaluation phase and may be detected during the analysis phase. Numeric overflow is an example of a dynamic error. ]

[Definition: A type error may be raised during the analysis or evaluation phase. During the analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs. ]

The outcome of the analysis phase is either success or one or more type errors and/or static errors. The result of the evaluation phase is either a result value, a type error, or a dynamic error.

If any expression (at any level) can be evaluated during the analysis phase (because all its explicit operands are known and it has no dependencies on the dynamic context), then any error in performing this evaluation may be reported as a static error. However, the fn:error() function must not be evaluated during the analysis phase. For example, an implementation is allowed (but not required) to treat the following expression as a static error, because it calls a constructor function with a constant string that is not in the lexical space of the target type:

xs:date("Next Tuesday")

If the Static Typing Feature is not in effect but an implementation can nevertheless determine during the analysis phase that an expression will necessarily raise a type error, the implementation may report that error during the analysis phase.

In addition to static errors, dynamic errors, and type errors, an XQuery implementation may raise warnings, either during the analysis phase or the evaluation phase. The circumstances in which warnings are raised, and the ways in which warnings are handled, are implementation-defined.

In addition to the errors defined in this specification, an implementation may raise a dynamic error if insufficient resources are available for processing a given expression. For example, an implementation may specify limitations on the maximum numbers or sizes of various objects. These limitations, and the consequences of exceeding them, are implementation-dependent.

2.5.2 Handling Dynamic Errors

Except as noted in this document, if any operand of an expression raises a dynamic error, the expression also raises a dynamic error. If an expression can validly return a value or raise a dynamic error, the implementation may choose to return the value or raise the dynamic error. For example, the logical expression expr1 and expr2 may return the value false if either operand returns false, or may raise a dynamic error if either operand raises a dynamic error.

If more than one operand of an expression raises an error, the implementation may choose which error is raised by the expression. For example, in this expression:

($x div $y) + xs:decimal($z)

both the sub-expressions ($x div $y) and xs:decimal($z) may raise an error. The implementation may choose which error is raised by the "+" expression. Once one operand raises an error, the implementation is not required, but is permitted, to evaluate any other operands.

[Definition: A dynamic error carries an error value, which may be a single item or an empty sequence.] For example, an error value might be an integer, a string, a QName, or an element. An implementation may provide a mechanism whereby an application-defined error handler can process error values and produce diagnostics; in the absence of such an error handler, the string value of the error value may be used directly as an error message.

A dynamic error may be raised by a built-in function or operator. For example, the div operator raises an error if its second operand equals zero.

An error can be raised explicitly by calling the fn:error function, which only raises an error and never returns a value. This function is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The fn:error function takes an optional item as its parameter, which is the error value. For example, the following function call raises a dynamic error whose error value is a string:

fn:error(fn:concat("Unexpected value ", fn:string($v)))

2.5.3 Errors and Optimization

Because different implementations may choose to evaluate or optimize an expression in different ways, the detection and reporting of dynamic errors is implementation-dependent.

When an implementation is able to evaluate an expression without evaluating some subexpression, the implementation is never required to evaluate that subexpression solely to determine whether it raises a dynamic error. For example, if a function parameter is never used in the body of the function, an implementation may choose whether to evaluate the expression bound to that parameter in a function call.

Similarly, in evaluating an expression, an implementation is not required to search for data whose only possible effect on the result would be to raise an error, as illustrated in the following examples.

  • If an implementation can find (for example, by using an index) that at least one item returned by $expr1 in the following example has the value 47, it is allowed to return true as the result of the some expression, without searching for another item returned by $expr1 that would raise an error because it is not an integer.

    some $x in $expr1 satisfies $x = 47
    
  • In the following example, if an implementation can find (for example, by using an index) the product element-nodes that have an id child with the value 47, it is allowed to return these nodes as the result of the path expression, without searching for another product node that would raise an error because it has an id child whose value is not an integer.

    //product[id = 47]
    

In some cases, an optimizer may be able to achieve substantial performance improvements by rearranging an expression so that the underlying operations are performed in a different order than that in which they are written. In such cases, errors may be raised that would not have been raised if the expression were evaluated as written. However, an expression must not be rearranged in a way that changes its result value in the absence of errors.

  • The expression in the following example cannot raise a casting error if it is evaluated exactly as written (i.e., left to right). An implementation is permitted, however, to reorder the predicates to achieve better performance (for example, by taking advantage of an index). This reordering could cause the expression to raise an error.

    $N[@x castable as xs:date][xs:date(@x) gt xs:date("2000-01-01")]
    

To avoid unexpected errors caused by reordering of expressions, tests that are designed to prevent dynamic errors should be expressed using conditional or typeswitch expressions. Conditional and typeswitch expressions raise only dynamic errors that occur in the branch that is actually selected.

  • Unlike the previous example, the following example cannot raise a dynamic error if @x is not castable into an xs:date.

    $N[if (@x castable as xs:date)
       then xs:date(@x) gt xs:date("2000-01-01")
       else false()]
    

2.6 Optional Features

XQuery defines several optional features, which are described in this section.

2.6.1 Schema Import Feature

[Definition: If the Schema Import Feature is supported, a Prolog may contain a schema import. Definitions from the imported schema are added to the in-scope schema definitions.] If more than one schema is imported, the definitions contained in these schemas are collected into a single pool of definitions. This pool of definitions must satisfy the conditions for schema validity set out in Sections 3 and 5 of [XML Schema] Part 1. In brief, the definitions must be valid, they must be complete, and they must be unique—that is, the pool of definitions must not contain two or more definitions with the same expanded QName in the same symbol space. If any of these conditions is violated, a static error is raised.[err:XQ0012]

If an XQuery implementation that does not support the Schema Import Feature encounters a schema import, it raises a static error.[err:XQ0009] In such an implementation, the in-scope type definitions consist only of predefined type definitions, as described in C.1 Static Context Components.

2.6.2 Static Typing Feature

[Definition: An XQuery implementation that does not support the Static Typing Feature is not required to raise type errors during the static analysis phase.] However, non-type-related static errors must be detected and raised during the static analysis phase.

2.6.3 Full Axis Feature

[Definition: The following axes are designated as optional axes: ancestor, ancestor-or-self, following, following-sibling, preceding, and preceding-sibling.]

[Definition: An XQuery implementation that supports the Full Axis Feature must support all the optional axes.] For an XQuery implementation that does not support the Full Axis Feature, the set of optional axes that are supported is implementation-defined. If an implementation encounters a reference to an optional axis that it does not support, it must raise a static error. [err:XQ0010]

Note that XQuery does not recognize the namespace axis (defined by XPath 1.0 and deprecated by XPath 2.0).

2.6.4 Module Feature

An XQuery implementation that does not support the Module Feature raises a static error [err:XQ0016] if it encounters a module declaration or a module import. Since a module declaration is required in a library module, the Module Feature is required in order to create a library module. In the absence of this feature, each query consists of a single main module.

2.6.5 Pragmas

[Definition: A pragma may be used to provide additional information to an XQuery implementation.] The use of a pragma does not negate the requirement to support normal XQuery functionality in the absence of the pragma.

[146]    Pragma    ::=    "(::" S? "pragma" S QName (S ExtensionContents)? "::)"
[148]    ExtensionContents    ::=    (Char* - (Char* '::)' Char*))

The QName of a Pragma must contain an explicit namespace prefix. Within a Pragma, the character content may consist of any sequence of characters that does not include the sequence "::)". Pragmas may be used anywhere that ignorable whitespace is allowed. See A.2 Lexical structure for the exact lexical states where pragmas are recognized. A pragma is identified by its QName.

If an implementation does not support a pragma, then that pragma shall be ignored. If an implementation does support a pragma and the implementation determines that the character content is invalid, then a static error is raised.[err:XQ0013] Otherwise, the effect of the pragma on the result of the Query is implementation-defined.

The following example shows how a pragma might be used:

declare namespace exq = "http://example.org/XQueryImplementation";
   (:: pragma exq:timeout 1000 ::)
   fn:count($doc//author)

An implementation that supports the exq:timeout pragma might raise a dynamic error if it is unable to count the authors within 1000 seconds. An implementation that does not support this pragma would execute as long as necessary to count the authors.

2.6.6 Must-Understand Extensions

[Definition: An implementation may extend XQuery functionality by supporting must-understand extensions. A must-understand extension may be used anywhere that ignorable whitespace is allowed.]

[147]    MUExtension    ::=    "(::" S? "extension" S QName (S ExtensionContents)? "::)"
[148]    ExtensionContents    ::=    (Char* - (Char* '::)' Char*))

A must-understand extension is identified by its QName, which must contain an explicit namespace prefix. The character content may consist of any sequence of characters that does not include the sequence "::)". See A.2 Lexical structure for the exact lexical states where these extensions are recognized.

If an implementation does not support a must-understand extension, then a static error is raised.[err:XQ0014] If an implementation does support a must-understand extension and the implementation determines that the character content is invalid, then a static error is raised. Otherwise, the effect of the must-understand extension on the result of the Query is implementation-defined.

The following example shows how a must-understand extension might be used:

   declare namespace exq = "http://example.org/XQueryImplementation";

   for $e in fn:doc("employees.xml")//employee
   order by $e/lastname (:: extension exq:RightToLeft ::)
   return $e

An implementation that supports the exq:RightToLeft extension might order the last names by examining characters from right to left instead of from left to right. An implementation that does not support this extension would raise a static error.

2.6.6.1 XQuery Flagger

[Definition: An XQuery Flagger is a facility that is provided by an implementation that is able to identify queries that contain must-understand extensions. If an implementation supports must-understand extensions, then an XQuery Flagger must be provided.] The XQuery Flagger is disabled by default; the mechanism by which the XQuery Flagger is enabled is implementation-defined. If the XQuery Flagger is enabled, a static error [err:XQ0015] is raised if the query contains a must-understand extension.

An XQuery Flagger is provided to assist programmers in producing queries that are portable among multiple conforming XQuery implementations.

The following example illustrates how an XQuery Flagger might be used:

xquery RightToLeft.xquery -Flagger=on

If RightToLeft.xquery contains a must-understand extension such as exq:RightToLeft, then this XQuery invocation will result in a static error. If the XQuery Flagger was not enabled and the implementation supports exq:RightToLeft, then this query might execute without error.

2.6.7 Static Typing Extensions

In some cases, the static typing rules defined in [XQuery 1.0 and XPath 2.0 Formal Semantics] are not very precise (see, for instance, the type inference rules for the ancestor axes—parent, ancestor, and ancestor-or-self—and for the function fn:root). Some implementations may wish to support more precise static typing rules.

A conforming implementation may provide a static typing extension. [Definition: A static typing extension is a type inference rule that infers a more precise static type than that inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics].] That is, given an expression E, and its static type T inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics], an implementation may infer a static type T1 for E such that T1 is a subtype of T (that is, all instances of T1 are also instances of T).

Note:

It is not recommended for a static typing extension to change the static type behavior of the treat expression, since static type behavior is central to the semantics of this expression.

2.6.7.1 XQuery Static Flagger

[Definition: An XQuery Static Flagger is a facility that is able to identify queries that require a static typing extension.] If an implementation supports static typing extensions, then it must also provide an XQuery Static Flagger. The XQuery Static Flagger is disabled by default; the mechanism by which it is enabled is implementation-defined. When enabled, the XQuery Static Flagger must raise a static error during the static analysis phase wherever a type error is called for by the rules in [XQuery 1.0 and XPath 2.0 Formal Semantics]. The purpose of an XQuery Static Flagger is to assist programmers in producing queries that are portable among multiple conforming XQuery implementations.

The following example illustrates how an XQuery Static Flagger might be used:

xquery abc.xquery -StaticFlagger=on

If abc.xquery contains a type error according to the static semantic rules in [XQuery 1.0 and XPath 2.0 Formal Semantics], then this XQuery invocation will result in a static error. If the XQuery Static Flagger was not enabled and the implementation supports a static typing extension, then this query might execute without error.

2.7 Comments

[149]    Comment    ::=    "(:" (CommentContents | Comment)* ":)"
[150]    CommentContents    ::=    (Char+ - (Char* ':)' Char*))

Comments may be used to provide informative annotation for a query, either in the Prolog or in the Query Body. Comments are lexical constructs only, and do not affect query processing.

Comments are strings, delimited by the symbols (: and :). Comments may be nested.

A comment may be used anywhere ignorable whitespace is allowed. See A.2 Lexical structure for the exact lexical states where comments are recognized.

The following is an example of a comment:

(: Houston, we have a problem :)

3 Expressions

This section discusses each of the basic kinds of expression. Each kind of expression has a name such as PathExpr, which is introduced on the left side of the grammar production that defines the expression. Since XQuery is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.

The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [A XQuery Grammar].

[26]    Expr    ::=    ExprSingle ("," ExprSingle)*
[27]    ExprSingle    ::=    FLWORExpr
| QuantifiedExpr
| TypeswitchExpr
| IfExpr
| OrExpr

A query may consist of one or more modules, as described in 4 Modules and Prologs. If a query is executable, one of its modules has a Query Body containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol Expr.

The XQuery operator that has lowest precedence is the comma operator (described in 3.3.1 Constructing Sequences), which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (Expr) can consist of two operands (ExprSingle) separated by a comma. The name ExprSingle denotes an expression that does not contain a top-level comma operator (despite its name, an ExprSingle may evaluate to a sequence containing more than one item.)

The symbol ExprSingle is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be an ExprSingle, because commas are used to separate the arguments of a function call.

After the comma, the expressions that have next lowest precedence are FLWORExpr, QuantifiedExpr, TypeswitchExpr, IfExpr, and OrExpr. Each of these expressions is described in a separate section of this document.

3.1 Primary Expressions

[Definition: Primary expressions are the basic primitives of the language. They include literals, variable references, context item expressions, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] Constructors are described in 3.7 Constructors.

[75]    PrimaryExpr    ::=    Literal | VarRef | ParenthesizedExpr | ContextItemExpr | FunctionCall | Constructor | OrderedExpr | UnorderedExpr

3.1.1 Literals

[Definition: A literal is a direct syntactic representation of an atomic value.] XQuery supports two kinds of literals: numeric literals and string literals.

[76]    Literal    ::=    NumericLiteral | StringLiteral
[77]    NumericLiteral    ::=    IntegerLiteral | DecimalLiteral | DoubleLiteral
[131]    IntegerLiteral    ::=    Digits
[132]    DecimalLiteral    ::=    ("." Digits) | (Digits "." [0-9]*)
[133]    DoubleLiteral    ::=    (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits
[134]    StringLiteral    ::=    ('"' (PredefinedEntityRef | CharRef | ('"' '"') | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | ("'" "'") | [^'&])* "'")
[139]    PredefinedEntityRef    ::=    "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";"
[138]    Digits    ::=    [0-9]+

The value of a numeric literal containing no "." and no e or E character is an atomic value of type xs:integer. The value of a numeric literal containing "." but no e or E character is an atomic value of type xs:decimal. The value of a numeric literal containing an e or E character is an atomic value of type xs:double. Values of numeric literals are interpreted according to the rules in [XML Schema].

The value of a string literal is an atomic value whose type is xs:string and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.

A string literal may contain a predefined entity reference, which is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance. Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XQuery are as follows:

Entity Reference Character Represented
&lt; <
&gt; >
&amp; &
&quot; "
&apos; '

A string literal may also contain a character reference, which is an XML-style reference to a Unicode character, identified by its decimal or hexadecimal code point. For example, the Euro symbol (€) can be represented by the character reference &#8364;. Character references are formally defined in Section 4.1 of [XML 1.0] or [XML 1.1] (which definition applies is implementation-defined).

Here are some examples of literal expressions:

  • "12.5" denotes the string containing the characters '1', '2', '.', and '5'.

  • 12 denotes the integer value twelve.

  • 12.5 denotes the decimal value twelve and one half.

  • 125E2 denotes the double value twelve thousand, five hundred.

  • "He said, ""I don't like it.""" denotes a string containing two quotation marks and one apostrophe.

  • "Ben &amp; Jerry&apos;s" denotes the string "Ben & Jerry's".

  • "&#8364;99.50" denotes the string "€99.50".

The boolean values true and false can be represented by calls to the built-in functions fn:true() and fn:false(), respectively.

Values of other atomic types can be constructed by calling the constructor for the given type. The constructors for XML Schema built-in types are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:

  • xs:integer("12") returns the integer value twelve.

  • xs:date("2001-08-25") returns an item whose type is xs:date and whose value represents the date 25th August 2001.

  • xdt:dayTimeDuration("PT5H") returns an item whose type is xdt:dayTimeDuration and whose value represents a duration of five hours.

It is also possible to construct values of various types by using a cast expression. For example:

  • 9 cast as hatsize returns the atomic value 9 whose type is hatsize.

3.1.2 Variable References

[78]    VarRef    ::=    "$" VarName
[136]    VarName    ::=    QName

A variable reference is a QName preceded by a $-sign. Two variable references are equivalent if their local names are the same and their namespace prefixes are bound to the same namespace URI in the statically known namespaces. An unprefixed variable reference is in no namespace.

Every variable reference must match a name in the in-scope variables, which include variables from the following sources:

  1. A variable may be declared in a Prolog, in the current module or an imported module. See 4 Modules and Prologs for a discussion of modules and Prologs.

  2. A variable may be added to the in-scope variables by the host language environment.

  3. A variable may be bound by an XQuery expression. The kinds of expressions that can bind variables are FLWOR expressions (3.8 FLWOR Expressions), quantified expressions (3.11 Quantified Expressions), and typeswitch expressions (3.12.2 Typeswitch). Function calls also bind values to the formal parameters of functions before executing the function body.

Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a static error [err:XP0008] to reference a variable that is not in scope. If a variable is bound in the static context for an expression, that variable is in scope for the entire expression.

If a variable reference matches two or more variable bindings that are in scope, then the reference is taken as referring to the inner binding, that is, the one whose scope is smaller. At evaluation time, the value of a variable reference is the value of the expression to which the relevant variable is bound. The scope of a variable binding is defined separately for each kind of expression that can bind variables.

3.1.3 Parenthesized Expressions

[79]    ParenthesizedExpr    ::=    "(" Expr? ")"

Parentheses may be used to enforce a particular evaluation order in expressions that contain multiple operators. For example, the expression (2 + 4) * 5 evaluates to thirty, since the parenthesized expression (2 + 4) is evaluated first and its result is multiplied by five. Without parentheses, the expression 2 + 4 * 5 evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.

Empty parentheses are used to denote an empty sequence, as described in 3.3.1 Constructing Sequences.

3.1.4 Context Item Expression

[80]    ContextItemExpr    ::=    "."

A context item expression evaluates to the context item, which may be either a node (as in the expression fn:doc("bib.xml")//book[fn:count(./author)>1]) or an atomic value (as in the expression (1 to 100)[. mod 5 eq 0]).

If the context item is undefined, a context item expression raises a dynamic error.[err:XP0002]

3.1.5 Function Calls

A function call consists of a QName followed by a parenthesized list of zero or more expressions, called arguments. If the QName in the function call has no namespace prefix, it is considered to be in the default function namespace.

If the expanded QName and number of arguments in a function call do not match the name and arity of a function signature in the static context, a static error is raised.[err:XP0017]

[83]    FunctionCall    ::=    QName "(" (ExprSingle ("," ExprSingle)*)? ")"

XQuery allows functions to be called. A core library of functions is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. Additional functions may be declared in a Prolog, imported from a library module, or provided by the external environment as part of the static context. For details on processing function names that have no namespace prefix, see 4.7 Default Namespace Declaration.

A function call is evaluated as follows:

  1. Argument expressions are evaluated, producing argument values. The order of argument evaluation is implementation-dependent and a function need not evaluate an argument if the function can evaluate its body without evaluating that argument.

  2. Each argument value is converted by applying the function conversion rules listed below.

  3. If the function is a built-in function, it is evaluated using the converted argument values. The result is a value of the function's declared return type.

  4. If the function is a user-declared function, the converted argument values are bound to the formal parameters of the function, and the function body is evaluated. The value returned by the function body is then converted to the declared return type of the function by applying the function conversion rules.

    When a converted argument value is bound to a function parameter, the argument value retains its most specific dynamic type, even though this may be a subtype of the type of the formal parameter. For example, a function with a parameter $p of type xs:decimal can be invoked with an argument of type xs:integer, which is derived from xs:decimal. During the processing of this function invocation, the dynamic type of $p inside the body of the function is considered to be xs:integer. Similarly, the value returned by a function retains its most specific type, which may be a subtype of the declared return type of the function. For example, a function that has a declared return type of xs:decimal may in fact return a value of dynamic type xs:integer.

    During execution of a function body, the static context and dynamic context for expression evaluation are defined by the module resource in which the function is declared, which is not necessarily the same as the module resource in which the function is called. As an example of this rule, a function does not inherit a focus (context item, context position, and context size) from the calling environment. During evaluation of a function body, the focus is undefined, except where it is defined by the action of some expression inside the function body. It is a static error [err:XP0018] for an expression to depend on the focus when the focus is undefined.

The function conversion rules are used to convert an argument value or a return value to its expected type; that is, to the declared type of the function parameteror return. The expected type is expressed as a SequenceType. The function conversion rules are applied to a given value as follows:

  • If the expected type is a sequence of an atomic type (possibly with an occurrence indicator *, +, or ?), the following conversions are applied:

    1. Atomization is applied to the given value, resulting in a sequence of atomic values.

    2. Each item in the atomic sequence that is of type xdt:untypedAtomic is cast to the expected atomic type. For built-in functions where the expected type is specified as numeric, arguments of type xdt:untypedAtomic are cast to xs:double.

    3. For each numeric item in the atomic sequence that can be promoted to the expected atomic type using the promotion rules in B.1 Type Promotion, the promotion is done.

  • If, after the above conversions, the resulting value does not match the expected type according to the rules for SequenceType Matching, a type error is raised. [err:XP0004][err:XP0006] If the function call takes place in a module resource other than the module resource in which the function is defined, this rule must be satisfied in both the module resource where the function is called and the module resource where the function is defined (the test is repeated because the two module resources may have different in-scope schema definitions.) Note that the rules for SequenceType Matching permit a value of a derived type to be substituted for a value of its base type.

Since the arguments of a function call are separated by commas, any argument expression that contains a top-level comma operator must be enclosed in parentheses. Here are some illustrative examples of function calls:

  • my:three-argument-function(1, 2, 3) denotes a function call with three arguments.

  • my:two-argument-function((1, 2), 3) denotes a function call with two arguments, the first of which is a sequence of two values.

  • my:two-argument-function(1, ()) denotes a function call with two arguments, the second of which is an empty sequence.

  • my:one-argument-function((1, 2, 3)) denotes a function call with one argument that is a sequence of three values.

  • my:one-argument-function(( )) denotes a function call with one argument that is an empty sequence.

  • my:zero-argument-function( ) denotes a function call with zero arguments.

3.2 Path Expressions

A path expression can be used to locate nodes within trees.

[59]    PathExpr    ::=    ("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
[60]    RelativePathExpr    ::=    StepExpr (("/" | "//") StepExpr)*

A path expression consists of a series of one or more steps, separated by "/" or "//", and optionally beginning with "/" or "//". An initial "/" or "//" is an abbreviation for one or more initial steps that are implicitly added to the beginning of the path expression, as described below.

A path expression consisting of a single step is evaluated as described in 3.2.1 Steps.

Each occurrence of "//" in a path expression is expanded as described in 3.2.4 Abbreviated Syntax, leaving a sequence of steps separated by "/". This sequence of steps is then evaluated from left to right. Each operation E1/E2 is evaluated as follows: Expression E1 is evaluated, and if the result is not a (possibly empty) sequence of nodes, a type error is raised.[err:XP0019] Each node resulting from the evaluation of E1 then serves in turn to provide an inner focus for an evaluation of E2, as described in 2.1.2 Dynamic Context. Each evaluation of E2 must result in a (possibly empty) sequence of nodes; otherwise, a type error is raised.[err:XP0019] The sequences of nodes resulting from all the evaluations of E2 are combined, and duplicate nodes are eliminated based on node identity. If ordering mode is ordered, the resulting node sequence is returned in document order; otherwise it is returned in implementation-dependent order.

As an example of a path expression, child::div1/child::para selects the para element children of the div1 element children of the context node, or, in other words, the para element grandchildren of the context node that have div1 parents.

A "/" at the beginning of a path expression is an abbreviation for the initial step fn:root(self::node()) treat as document-node() (this is true even if the "/" is the entire path expression). The effect of this initial step is to begin the path at the root node of the tree that contains the context node. If the context item is not a node, a type error is raised.[err:XP0020] At evaluation time, if the root node above the context node is not a document node, a dynamic error is raised.[err:XP0050]

A "//" at the beginning of a path expression is an abbreviation for the initial steps fn:root(self::node()) treat as document-node()/descendant-or-self::node(). The effect of these initial steps is to establish an initial node sequence that contains the root of the tree in which the context node is found, plus all nodes descended from this root. This node sequence is used as the input to subsequent steps in the path expression. If the context item is not a node, a type error is raised.[err:XP0020] At evaluation time, if the root node above the context node is not a document node, a dynamic error is raised.[err:XP0050]

Note:

The descendants of a node do not include attribute nodes.

Note:

The "/" character can be used either as an individual token or as part of a pattern such as "/*". This can cause parsing difficulties when "/" appears on the left hand side of an operator. For example, "/*" is a valid path expression with a wildcard, but "/*5" and "/ * 5" raise parsing errors. Parentheses must be used when "/" is used as the first operand of an operator, as in "(/) * 5". Similarly, "4 + / * 5" raises a parsing error, but "4 + (/) * 5" is a valid expression. The expression 4 + /" is also valid, because / does not occur on the left hand side of the operator.

3.2.1 Steps

[61]    StepExpr    ::=    AxisStep | FilterExpr
[62]    AxisStep    ::=    (ForwardStep | ReverseStep) PredicateList
[63]    ForwardStep    ::=    (ForwardAxis NodeTest) | AbbrevForwardStep
[66]    ReverseStep    ::=    (ReverseAxis NodeTest) | AbbrevReverseStep
[73]    PredicateList    ::=    Predicate*

A step generates a sequence of items and then filters the sequence by zero or more predicates. The value of the step consists of those items that satisfy the predicates. Predicates are described in 3.2.2 Predicates. A step may be either an axis step or a filter expression. Filter expressions are described in 3.3.2 Filter Expressions.

The result of an axis step is always a sequence of zero or more nodes, and these nodes are always returned in document order. An axis step may be either a forward step or a reverse step, followed by zero or more predicates. An axis step might be thought of as beginning at the context node and navigating to those nodes that are reachable from the context node via a specified axis. Such a step has two parts: an axis, which defines the "direction of movement" for the step, and a node test, which selects nodes based on their kind, name, and/or type. If the context item is not a node, a type error is raised.[err:XP0020]

In the abbreviated syntax for a step, the axis can be omitted and other shorthand notations can be used as described in 3.2.4 Abbreviated Syntax.

The unabbreviated syntax for an axis step consists of the axis name and node test separated by a double colon. The result of the step consists of the nodes reachable from the context node via the specified axis that have the node kind, name, and/or type specified by the node test. For example, the step child::para selects the para element children of the context node: child is the name of the axis, and para is the name of the element nodes to be selected on this axis. The available axes are described in 3.2.1.1 Axes. The available node tests are described in 3.2.1.2 Node Tests. Examples of steps are provided in 3.2.3 Unabbreviated Syntax and 3.2.4 Abbreviated Syntax.

3.2.1.1 Axes
[64]    ForwardAxis    ::=    ("child" "::")
| ("descendant" "::")
| ("attribute" "::")
| ("self" "::")
| ("descendant-or-self" "::")
| ("following-sibling" "::")
| ("following" "::")
[67]    ReverseAxis    ::=    ("parent" "::")
| ("ancestor" "::")
| ("preceding-sibling" "::")
| ("preceding" "::")
| ("ancestor-or-self" "::")

XQuery supports the following axes (subject to limitations as described in 2.6.3 Full Axis Feature):

  • The child axis contains the children of the context node, which are the nodes returned by the dm:children accessor in [XQuery 1.0 and XPath 2.0 Data Model].

    Note:

    Only document nodes and element nodes have children. If the context node is any other kind of node, or if the context node is an empty document or element node, then the child axis is an empty sequence. The children of a document node or element node may be element, processing instruction, comment, or text nodes. Attribute and document nodes can never appear as children.

  • the descendant axis is defined as the transitive closure of the child axis; it contains the descendants of the context node (the children, the children of the children, and so on)

  • the parent axis contains the sequence returned by the dm:parent accessor in [XQuery 1.0 and XPath 2.0 Data Model], which returns the parent of the context node, or an empty sequence if the context node has no parent

  • the ancestor axis is defined as the transitive closure of the parent axis; it contains the ancestors of the context node (the parent, the parent of the parent, and so on)

    Note:

    The ancestor axis includes the root node of the tree in which the context node is found, unless the context node is the root node.

  • the following-sibling axis contains the context node's following siblings, those children of the context node's parent that occur after the context node in document order; if the context node is an attribute node, the following-sibling axis is empty

  • the preceding-sibling axis contains the context node's preceding siblings, those children of the context node's parent that occur before the context node in document order; if the context node is an attribute node, the preceding-sibling axis is empty

  • the following axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not descendants of the context node, and occur after the context node in document order

  • the preceding axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not ancestors of the context node, and occur before the context node in document order

  • the attribute axis contains the attributes of the context node, which are the nodes returned by the dm:attributes accessor in [XQuery 1.0 and XPath 2.0 Data Model]; the axis will be empty unless the context node is an element

  • the self axis contains just the context node itself

  • the descendant-or-self axis contains the context node and the descendants of the context node

  • the ancestor-or-self axis contains the context node and the ancestors of the context node; thus, the ancestor-or-self axis will always include the root node

Axes can be categorized as forward axes and reverse axes. An axis that only ever contains the context node or nodes that are after the context node in document order is a forward axis. An axis that only ever contains the context node or nodes that are before the context node in document order is a reverse axis.

The parent, ancestor, ancestor-or-self, preceding, and preceding-sibling axes are reverse axes; all other axes are forward axes. The ancestor, descendant, following, preceding and self axes partition a document (ignoring attribute nodes): they do not overlap and together they contain all the nodes in the document.

In a sequence of nodes selected by an axis step, each node is assigned a context position that corresponds to its position in the sequence. If the axis is a forward axis, context positions are assigned to the nodes in document order, starting with 1. If the axis is a reverse axis, context positions are assigned to the nodes in reverse document order, starting with 1. This makes it possible to select a node from the sequence by specifying its position.

Note:

One example of an expression that uses the context position is a numeric predicate. The expression child::para[1] selects the first para element that is a child of the context node.

3.2.1.2 Node Tests

[Definition: A node test is a condition that must be true for each node selected by a step.] The condition may be based on the kind of the node (element, attribute, text, document, comment, or processing instruction), the name of the node, or (in the case of element, attribute, and document nodes), the type of the node.

[69]    NodeTest    ::=    KindTest | NameTest
[70]    NameTest    ::=    QName | Wildcard
[71]    Wildcard    ::=    "*"
| (NCName ":" "*")
| ("*" ":" NCName)

[Definition: Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain.] Thus:

  • For the attribute axis, the principal node kind is attribute.

  • For all other axes, the principal node kind is element.

[Definition: A node test that consists only of a QName or a Wildcard is called a name test.] A name test is true if and only if the kind of the node is the principal node kind and the expanded QName of the node is equal (on a codepoint basis) to the expanded QName specified by the name test. For example, child::para selects the para element children of the context node; if the context node has no para children, it selects an empty set of nodes. attribute::abc:href selects the attribute of the context node with the QName abc:href; if the context node has no such attribute, it selects an empty set of nodes.

A QName in a name test is resolved into an expanded QName using the statically known namespaces in the expression context. It is a static error [err:XP0008] if the QName has a prefix that does not correspond to any statically known namespace. An unprefixed QName, when used as a name test on an axis whose principal node kind is element, has the namespace URI of the default element/type namespace in the expression context; otherwise, it has no namespace URI.

A name test is not satisfied by an element node whose name does not match the QName of the name test, even if it is in a substitution group whose head is the named element.

A node test * is true for any node of the principal node kind. For example, child::* will select all element children of the context node, and attribute::* will select all attributes of the context node.

A node test can have the form NCName:*. In this case, the prefix is expanded in the same way as with a QName, using the statically known namespaces in the static context. If the prefix is not found in the statically known namespaces, a static error is raised.[err:XP0008] The node test is true for any node of the principal node kind whose expanded QName has the namespace URI to which the prefix is bound, regardless of the local part of the name.

A node test can also have the form *:NCName. In this case, the node test is true for any node of the principal node kind whose local name matches the given NCName, regardless of its namespace.

[Definition: An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.] The syntax and semantics of a kind test are described in 2.4 Types. When a kind test is used in a node test, only those nodes on the designated axis that match the kind test are selected. Shown below are several examples of kind tests that might be used in path expressions:

  • node() matches any node.

  • text() matches any text node.

  • comment() matches any comment node.

  • element() matches any element node.

  • element(person) matches any element node whose name is person (or is in the substitution group headed by person), and whose type annotation conforms to the top-level element declaration for a person element.

  • element(person, *) matches any element node whose name is person (or is in the substitution group headed by person), without any restriction on type annotation.

  • element(person, surgeon) matches any element node whose name is person (or is in the substitution group headed by person), and whose type annotation is surgeon.

  • element(*, surgeon) matches any element node whose type annotation is surgeon, regardless of its name.

  • element(hospital/staff/person) matches any element node whose name and type annotation conform to the schema declaration of a person element in a staff element in a hospital element whose declaration is a top-level element declaration.

  • attribute() matches any attribute node.

  • attribute(price, *) matches any attribute whose name is price, regardless of its type annotation.

  • attribute(*, xs:decimal) matches any attribute whose type annotation is xs:decimal, regardless of its name.

  • document-node() matches any document node.

  • document-node(element(book)) matches any document node whose content consists of a single element node that satisfies the kind test element(book), mixed with zero or more comments and processing instructions.

3.2.2 Predicates

[74]    Predicate    ::=    "[" Expr "]"

A predicate consists of an expression, called a predicate expression, enclosed in square brackets. A predicate serves to filter a sequence, retaining some items and discarding others. For each item in the sequence to be filtered, the predicate expression is evaluated using an inner focus derived from that item, as described in 2.1.2 Dynamic Context. The result of the predicate expression is coerced to a xs:boolean value, called the predicate truth value, as described below. Those items for which the predicate truth value is true are retained, and those for which the predicate truth value is false are discarded.

The predicate truth value is derived by applying the following rules, in order:

  1. If the value of the predicate expression is an atomic value of a numeric type, the predicate truth value is true if the value of the predicate expression is equal (by the eq operator) to the context position, and is false otherwise.

  2. Otherwise, the predicate truth value is the effective boolean value of the predicate expression.

Here are some examples of axis steps that contain predicates:

  • This example selects the second chapter element that is a child of the context node:

    child::chapter[2]
    
  • This example selects all the descendants of the context node that are elements named "toy" and whose color attribute has the value "red":

    descendant::toy[attribute::color = "red"]
    
  • This example selects all the employee children of the context node that have a secretary child element:

    child::employee[secretary]
    

When using predicates with a sequence of nodes selected using a reverse axis, it is important to remember that the the context positions for such a sequence are assigned in reverse document order. For example, preceding::foo[1] returns the first qualifying foo element in reverse document order, because the predicate is part of an axis step using a reverse axis. By contrast, (preceding::foo)[1] returns the first qualifying foo element in document order, because the parentheses cause (preceding::foo) to be parsed as a primary expression in which context positions are assigned in document order. Similarly, ancestor::*[1] returns the nearest ancestor element, because the ancestor axis is a reverse axis, whereas (ancestor::*)[1] returns the root element (first ancestor in document order).

3.2.3 Unabbreviated Syntax

This section provides a number of examples of path expressions in which the axis is explicitly specified in each step. The syntax used in these examples is called the unabbreviated syntax. In many common cases, it is possible to write path expressions more concisely using an abbreviated syntax, as explained in 3.2.4 Abbreviated Syntax.

  • child::para selects the para element children of the context node

  • child::* selects all element children of the context node

  • child::text() selects all text node children of the context node

  • child::node() selects all the children of the context node, whatever their node type

  • attribute::name selects the name attribute of the context node

  • attribute::* selects all the attributes of the context node

  • parent::node() selects the parent of the context node. If the context node is an attribute node, this expression returns the element node (if any) to which the attribute node is attached.

  • descendant::para selects the para element descendants of the context node

  • ancestor::div selects all div ancestors of the context node

  • ancestor-or-self::div selects the div ancestors of the context node and, if the context node is a div element, the context node as well

  • descendant-or-self::para selects the para element descendants of the context node and, if the context node is a para element, the context node as well

  • self::para selects the context node if it is a para element, and otherwise selects nothing

  • child::chapter/descendant::para selects the para element descendants of the chapter element children of the context node

  • child::*/child::para selects all para grandchildren of the context node

  • / selects the root of the tree that contains the context node, but raises a dynamic error if this root is not a document node

  • /descendant::para selects all the para elements in the same document as the context node

  • /descendant::list/child::member selects all the member elements that have a list parent and that are in the same document as the context node

  • child::para[fn:position() = 1] selects the first para child of the context node

  • child::para[fn:position() = fn:last()] selects the last para child of the context node

  • child::para[fn:position() = fn:last()-1] selects the last but one para child of the context node

  • child::para[fn:position() > 1] selects all the para children of the context node other than the first para child of the context node

  • following-sibling::chapter[fn:position() = 1]selects the next chapter sibling of the context node

  • preceding-sibling::chapter[fn:position() = 1]selects the previous chapter sibling of the context node

  • /descendant::figure[fn:position() = 42] selects the forty-second figure element in the document containing the context node

  • /child::book/child::chapter[fn:position() = 5]/child::section[fn:position() = 2] selects the second section of the fifth chapter of the book whose parent is the document node that contains the context node

  • child::para[attribute::type="warning"]selects all para children of the context node that have a type attribute with value warning

  • child::para[attribute::type='warning'][fn:position() = 5]selects the fifth para child of the context node that has a type attribute with value warning

  • child::para[fn:position() = 5][attribute::type="warning"]selects the fifth para child of the context node if that child has a type attribute with value warning

  • child::chapter[child::title='Introduction']selects the chapter children of the context node that have one or more title children whose typed value is equal to the string Introduction

  • child::chapter[child::title] selects the chapter children of the context node that have one or more title children

  • child::*[self::chapter or self::appendix] selects the chapter and appendix children of the context node

  • child::*[self::chapter or self::appendix][fn:position() = fn:last()] selects the last chapter or appendix child of the context node

3.2.4 Abbreviated Syntax

[65]    AbbrevForwardStep    ::=    "@"? NodeTest
[68]    AbbrevReverseStep    ::=    ".."

The abbreviated syntax permits the following abbreviations:

  1. The attribute axis attribute:: can be abbreviated by @. For example, a path expression para[@type="warning"] is short for child::para[attribute::type="warning"] and so selects para children with a type attribute with value equal to warning.

  2. If the axis name is omitted from an axis step, the default axis is child unless the axis step contains an AttributeTest; in that case, the default axis is attribute. For example, the path expression section/para is an abbreviation for child::section/child::para, and the path expression section/@id is an abbreviation for child::section/attribute::id. Similarly, section/attribute(id) is an abbreviation for child::section/attribute::attribute(id). Note that the latter expression contains both an axis specification and a node test.

  3. // is effectively replaced by /descendant-or-self::node()/ during processing of a path expression. For example, //para is an abbreviation for /descendant-or-self::node()/child::para and so will select any para element in the document (even a para element that is a document element will be selected by //para since the document element node is a child of the root node); div1//para is short for child::div1/descendant-or-self::node()/child::para and so will select all para descendants of div1 children.

    Note:

    The path expression //para[1] does not mean the same as the path expression /descendant::para[1]. The latter selects the first descendant para element; the former selects all descendant para elements that are the first para children of their respective parents.

  4. A step consisting of .. is short for parent::node(). For example, ../title is short for parent::node()/child::title and so will select the title children of the parent of the context node.

    Note:

    The expression ., known as a context item expression, is a primary expression, and is described in 3.1.4 Context Item Expression.

Here are some examples of path expressions that use the abbreviated syntax:

  • para selects the para element children of the context node

  • * selects all element children of the context node

  • text() selects all text node children of the context node

  • @name selects the name attribute of the context node

  • @* selects all the attributes of the context node

  • para[1] selects the first para child of the context node

  • para[fn:last()] selects the last para child of the context node

  • */para selects all para grandchildren of the context node

  • /book/chapter[5]/section[2] selects the second section of the fifth chapter of the book whose parent is the document node that contains the context node

  • chapter//para selects the para element descendants of the chapter element children of the context node

  • //para selects all the para descendants of the root document node and thus selects all para elements in the same document as the context node

  • //@version selects all the version attribute nodes that are in the same document as the context node

  • //list/member selects all the member elements in the same document as the context node that have a list parent

  • .//para selects the para element descendants of the context node

  • .. selects the parent of the context node

  • ../@lang selects the lang attribute of the parent of the context node

  • para[@type="warning"] selects all para children of the context node that have a type attribute with value warning

  • para[@type="warning"][5] selects the fifth para child of the context node that has a type attribute with value warning

  • para[5][@type="warning"] selects the fifth para child of the context node if that child has a type attribute with value warning

  • chapter[title="Introduction"] selects the chapter children of the context node that have one or more title children whose typed value is equal to the string Introduction

  • chapter[title] selects the chapter children of the context node that have one or more title children

  • employee[@secretary and @assistant] selects all the employee children of the context node that have both a secretary attribute and an assistant attribute

  • book/(chapter|appendix)/section selects every section element that has a parent that is either a chapter or an appendix element, that in turn is a child of a book element that is a child of the context node.

  • If E is any expression that returns a sequence of nodes, then the expression E/. returns the same nodes in document order, with duplicates eliminated based on node identity.

3.3 Sequence Expressions

XQuery supports operators to construct, filter, and combine sequences of items. Sequences are never nested—for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3).

3.3.1 Constructing Sequences

[26]    Expr    ::=    ExprSingle ("," ExprSingle)*
[44]    RangeExpr    ::=    AdditiveExpr ( "to" AdditiveExpr )?

One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting values, in order, into a single result sequence.

A sequence may contain duplicate values or nodes, but a sequence is never an item in another sequence. When a new sequence is created by concatenating two or more input sequences, the new sequence contains all the items of the input sequences and its length is the sum of the lengths of the input sequences.

In places where the grammar calls for ExprSingle, such as the arguments of a function call, any expression that contains a top-level comma operator must be enclosed in parentheses. Empty parentheses can be used to denote an empty sequence.

Here are some examples of expressions that construct sequences:

  • The result of this expression is a sequence of five integers:

    (10, 1, 2, 3, 4)
    
  • This expression combines four sequences of length one, two, zero, and two, respectively, into a single sequence of length five. The result of this expression is the sequence 10, 1, 2, 3, 4.

    (10, (1, 2), (), (3, 4))
    
  • The result of this expression is a sequence containing all salary children of the context node followed by all bonus children.

    (salary, bonus)
    
  • Assuming that $price is bound to the value 10.50, the result of this expression is the sequence 10.50, 10.50.

    ($price, $price)
    

A range expression can be used to construct a sequence of consecutive integers. Each of the operands of the to operator is converted as though it was an argument of a function with the expected parameter type xs:integer. A type error [err:XP0006] is raised if either operand cannot be converted to a single integer. If the integer derived from the first operand is greater than the integer derived from the second operand, the result of the range expression is an empty sequence. Otherwise, the result is a sequence containing the two integer operands and every integer between the two operands, in increasing order.

  • This example uses a range expression as one operand in constructing a sequence. It evaluates to the sequence 10, 1, 2, 3, 4.

    (10, 1 to 4)
    
  • This example constructs a sequence of length one containing the single integer 10.

    10 to 10
    
  • The result of this example is a sequence of length zero.

    15 to 10
    
  • This example uses the fn:reverse function to construct a sequence of six integers in decreasing order. It evaluates to the sequence 15, 14, 13, 12, 11, 10.

    fn:reverse(10 to 15)
    

3.3.2 Filter Expressions

[72]    FilterExpr    ::=    PrimaryExpr PredicateList
[73]    PredicateList    ::=    Predicate*

A filter expression consists simply of a primary expression followed by zero or more predicates. The result of the filter expression consists of all the items returned by the primary expression for which all the predicates are true. If no predicates are specified, the result is simply the result of the primary expression. This result may contain nodes, atomic values, or any combination of these. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression. Context positions are assigned to items based on their ordinal position in the result sequence. The first context position is 1.

Here are some examples of filter expressions:

  • Given a sequence of products in a variable, return only those products whose price is greater than 100.

    $products[price gt 100]
    
  • List all the integers from 1 to 100 that are divisible by 5. (See 3.3.1 Constructing Sequences for an explanation of the to operator.)

    (1 to 100)[. mod 5 eq 0]
    
  • The result of the following expression is the integer 25:

    (21 to 29)[5]
    
  • The following example illustrates the use of a filter expression as a step in a path expression. It returns the element node within the specified document whose ID value is "tiger":

    fn:doc("zoo.xml")/fn:id('tiger')
    

3.3.3 Combining Node Sequences

[47]    UnionExpr    ::=    IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
[48]    IntersectExceptExpr    ::=    InstanceofExpr ( ("intersect" | "except") InstanceofExpr )*

XQuery provides the following operators for combining sequences of nodes:

  • The union and | operators are equivalent. They take two node sequences as operands and return a sequence containing all the nodes that occur in either of the operands.

  • The intersect operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in both operands.

  • The except operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in the first operand but not in the second operand.

All these operators eliminate duplicate nodes from their result sequences based on node identity. If ordering mode is ordered, the resulting sequence is returned in document order; otherwise it is returned in implementation-dependent order.

If an operand of union, intersect, or except contains an item that is not a node, a type error is raised.[err:XP0004][err:XP0006]

Here are some examples of expressions that combine sequences. Assume the existence of three element nodes that we will refer to by symbolic names A, B, and C. Assume that the variables $seq1, $seq2 and $seq3 are bound to the following sequences of these nodes:

  • $seq1 is bound to (A, B)

  • $seq2 is bound to (A, B)

  • $seq3 is bound to (B, C)

Then:

  • $seq1 union $seq2 evaluates to the sequence (A, B).

  • $seq2 union $seq3 evaluates to the sequence (A, B, C).

  • $seq1 intersect $seq2 evaluates to the sequence (A, B).

  • $seq2 intersect $seq3 evaluates to the sequence containing B only.

  • $seq1 except $seq2 evaluates to the empty sequence.

  • $seq2 except $seq3 evaluates to the sequence containing A only.

In addition to the sequence operators described here, [XQuery 1.0 and XPath 2.0 Functions and Operators] includes functions for indexed access to items or sub-sequences of a sequence, for indexed insertion or removal of items in a sequence, and for removing duplicate items from a sequence.

3.4 Arithmetic Expressions

XQuery provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.

[45]    AdditiveExpr    ::=    MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
[46]    MultiplicativeExpr    ::=    UnionExpr ( ("*" | "div" | "idiv" | "mod") UnionExpr )*
[53]    UnaryExpr    ::=    ("-" | "+")* ValueExpr
[54]    ValueExpr    ::=    ValidateExpr | PathExpr

A subtraction operator must be preceded by whitespace if it could otherwise be interpreted as part of the previous token. For example, a-b will be interpreted as a name, but a - b and a -b will be interpreted as arithmetic operations.

An arithmetic expression is evaluated by applying the following rules, in order, until an error is raised or a value is computed:

  1. Atomization is applied to each operand.

  2. If either operand is now an empty sequence, the result of the operation is an empty sequence.

  3. If either operand is now a sequence of length greater than one, a type error is raised.[err:XP0006]

  4. If either operand is now of type xdt:untypedAtomic, it is cast to xs:double. If the cast fails, a dynamic error is raised.[err:XP0021]

  5. If the operand types are now valid for the given operator, the operator is applied to the operands, resulting in an atomic value or a dynamic error (for example, an error might result from dividing by zero.) The combinations of atomic types that are accepted by the various arithmetic operators, and their respective result types, are listed in B.2 Operator Mapping together with the functions in [XQuery 1.0 and XPath 2.0 Functions and Operators] that define the semantics of the operation for each type.

  6. If the operand types are still not valid for the given operator, a type error is raised.

XQuery supports two division operators named div and idiv. Each of these operators accepts two operands of any numeric type. As described in [XQuery 1.0 and XPath 2.0 Functions and Operators], $arg1 idiv $arg2 is equivalent to ($arg1 div $arg2) cast as xs:integer except for error cases.

Here are some examples of arithmetic expressions:

  • The first expression below returns the xs:decimal value -1.5, and the second expression returns the xs:integer value -1:

    -3 div 2
    -3 idiv 2
    
  • Subtraction of two date values results in a value of type xdt:dayTimeDuration:

    $emp/hiredate - $emp/birthdate
    
  • This example illustrates the difference between a subtraction operator and a hyphen:

    $unit-price - $unit-discount
    
  • Unary operators have higher precedence than binary operators, subject of course to the use of parentheses. Therefore, the following two examples have different meanings:

    -$bellcost + $whistlecost
    -($bellcost + $whistlecost)
    

Note:

Multiple consecutive unary arithmetic operators are permitted by XQuery for compatability with [XPath 1.0].

3.5 Comparison Expressions

Comparison expressions allow two values to be compared. XQuery provides three kinds of comparison expressions, called value comparisons, general comparisons, and node comparisons.

[43]    ComparisonExpr    ::=    RangeExpr ( (ValueComp
| GeneralComp
| NodeComp) RangeExpr )?
[56]    ValueComp    ::=    "eq" | "ne" | "lt" | "le" | "gt" | "ge"
[55]    GeneralComp    ::=    "=" | "!=" | "<" | "<=" | ">" | ">="
[57]    NodeComp    ::=    "is" | "<<" | ">>"

3.5.1 Value Comparisons

The value comparison operators are eq, ne, lt, le, gt, and ge. Value comparisons are used for comparing single values. The result of a value comparison is defined by applying the following rules, in order:

  1. Atomization is applied to each operand. If the result, called an atomized operand, contains more than one atomic value, a type error is raised.[err:XP0004][err:XP0006]

  2. If either atomized operand is an empty sequence, the result of the value comparison is an empty sequence.

  3. Any atomized operand that has the dynamic type xdt:untypedAtomic is cast to the type xs:string.

    Note:

    The purpose of this rule is to make value comparisons transitive. It is recognized that the general comparison operators have a different rule for casting of xdt:untypedAtomic operands. It is also recognized that transitivity of value comparisons may be compromised by loss of precision during type conversion (for example, two int values that differ slightly may both be considered equal to the same float value because float has less precision than int).

  4. If both atomized operands consist of exactly one atomic value, then the result of the comparison is true if the value of the first operand is (equal, not equal, less than, less than or equal, greater than, greater than or equal) to the value of the second operand; otherwise the result of the comparison is false. B.2 Operator Mapping defines which combinations of atomic types are comparable, and how the comparison operators are mapped into supporting functions. If the value of the first atomized operand is not comparable with the value of the second atomized operand, a type error is raised.[err:XP0004][err:XP0006]

Here are some examples of value comparisons:

  • The following comparison is true only if $book1 has exactly one author subelement and its typed value is "Kennedy" as an instance of xs:string or xdt:untypedAtomic. If $book1 has more than one author subelement, a type error is raised.[err:XP0004][err:XP0006] If $book1 has no author subelement, the result of the expression is the empty sequence.

    $book1/author eq "Kennedy"
    
  • The following path expression contains a predicate that selects products whose weight is greater than 100. For any product that does not have a weight subelement, the value of the predicate is the empty sequence, and the product is not selected:

    //product[weight gt 100]
    
  • The following comparisons are true because, in each case, the two constructed nodes have the same value after atomization, even though they have different identities and/or names:

    <a>5</a> eq <a>5</a>
    
    <a>5</a> eq <b>5</b>
    
  • The following comparison is true if my:hatsize and my:shoesize are both user-defined types that are derived by restriction from a primitive numeric type:

    my:hatsize(5) eq my:shoesize(5)
    

3.5.2 General Comparisons

The general comparison operators are =, !=, <, <=, >, and >=. General comparisons are existentially quantified comparisons that may be applied to operand sequences of any length. The result of a general comparison that does not raise an error is always true or false.

Atomization is applied to each operand of a general comparison. The result of the comparison is true if and only if there is a pair of atomic values, one belonging to the result of atomization of the first operand and the other belonging to the result of atomization of the second operand, that have the required magnitude relationship. Otherwise the result of the general comparison is false. The magnitude relationship between two atomic values is determined as follows:

  1. If either atomic value has the dynamic type xdt:untypedAtomic, that value is cast to a required type, which is determined as follows:

    1. If the dynamic type of the other atomic value is a numeric type, the required type is xs:double.

    2. If the dynamic type of the other atomic value is xdt:untypedAtomic, the required type is xs:string.

    3. Otherwise, the required type is the dynamic type of the other atomic value.

    If the cast to the required type fails, a dynamic error is raised.[err:XP0021]

    Note:

    The purpose of this rule is to preserve backward compatability with XPath 1.0, in which (for example) x < 17 is a numeric comparison if x is an untyped value. It is recognized that the value comparison operators have a different rule for casting of xdt:untypedAtomic operands.

  2. After any necessary casting, the atomic values are compared using one of the value comparison operators eq, ne, lt, le, gt, or ge, depending on whether the general comparison operator was =, !=, <, <=, >, or >=. The values have the required magnitude relationship if the result of this value comparison is true.

When evaluating a general comparison in which either operand is a sequence of items, an implementation may return true as soon as it finds an item in the first operand and an item in the second operand that have the required magnitude relationship. Similarly, a general comparison may raise a dynamic error as soon as it encounters an error in evaluating either operand, or in comparing a pair of items from the two operands. As a result of these rules, the result of a general comparison is not deterministic in the presence of errors.

Here are some examples of general comparisons:

  • The following comparison is true if the typed value of any author subelement of $book1 is "Kennedy" as an instance of xs:string or xdt:untypedAtomic:

    $book1/author = "Kennedy"
    
  • The following example contains three general comparisons. The value of the first two comparisons is true, and the value of the third comparison is false. This example illustrates the fact that general comparisons are not transitive.

    (1, 2) = (2, 3)
    (2, 3) = (3, 4)
    (1, 2) = (3, 4)
    
  • The following example contains two general comparisons, both of which are true. This example illustrates the fact that the = and != operators are not inverses of each other.

    (1, 2) = (2, 3)
    (1, 2) != (2, 3)
    
  • Suppose that $a, $b, and $c are bound to element nodes with type annotation xdt:untypedAtomic, with string values "1", "2", and "2.0" respectively. Then ($a, $b) = ($c, 3.0) returns false, because $b and $c are compared as strings. However, ($a, $b) = ($c, 2.0) returns true, because $b and 2.0 are compared as numbers.

3.5.3 Node Comparisons

Node comparisons are used to compare two nodes, by their identity or by their document order. The result of a node comparison is defined by applying the following rules, in order:

  1. Each operand must be either a single node or an empty sequence; otherwise a type error is raised.[err:XP0004][err:XP0006]

  2. If either operand is an empty sequence, the result of the comparison is an empty sequence.

  3. A comparison with the is operator is true if the two operands have the same identity, and are thus the same node; otherwise it is false. See [XQuery 1.0 and XPath 2.0 Data Model] for a definition of node identity.

  4. A comparison with the << operator returns true if the first operand node precedes the second operand node in document order; otherwise it returns false.

  5. A comparison with the >> operator returns true if the first operand node follows the second operand node in document order; otherwise it returns false.

Here are some examples of node comparisons:

  • The following comparison is true only if the left and right sides each evaluate to exactly the same single node:

    //book[isbn="1558604820"] is //book[call="QA76.9 C3845"]
    
  • The following comparison is false because each constructed node has its own identity:

    <a>5</a> is <a>5</a>
    
  • The following comparison is true only if the node identified by the left side occurs before the node identified by the right side in document order:

    //purchase[parcel="28-451"] << //sale[parcel="33-870"]
    

3.6 Logical Expressions

A logical expression is either an and-expression or an or-expression. If a logical expression does not raise an error, its value is always one of the boolean values true or false.

[41]    OrExpr    ::=    AndExpr ( "or" AndExpr )*
[42]    AndExpr    ::=    ComparisonExpr ( "and" ComparisonExpr )*

The first step in evaluating a logical expression is to find the effective boolean value of each of its operands (see 2.3.3 Effective Boolean Value).

The value of an and-expression is determined by the effective boolean values (EBV's) of its operands. If an error is raised during computation of one of the effective boolean values, an and-expression may raise a dynamic error, as shown in the following table:

AND: EBV2 = true EBV2 = false error in EBV2
EBV1 = true true false error
EBV1 = false false false false or error
error in EBV1 error false or error error

The value of an or-expression is determined by the effective boolean values (EBV's) of its operands. If an error is raised during computation of one of the effective boolean values, an or-expression may raise a dynamic error, as shown in the following table:

OR: EBV2 = true EBV2 = false error in EBV2
EBV1 = true true true true or error
EBV1 = false true false error
error in EBV1 true or error error error

The order in which the operands of a logical expression are evaluated is implementation-dependent. The tables above are defined in such a way that an or-expression can return true if the first expression evaluated is true, and it can raise an error if evaluation of the first expression raises an error. Similarly, an and-expression can return false if the first expression evaluated is false, and it can raise an error if evaluation of the first expression raises an error. As a result of these rules, a logical expression is not deterministic in the presence of errors, as described in 2.5.3 Errors and Optimization. This is illustrated in the examples below.

Here are some examples of logical expressions:

  • The following expressions return true:

    1 eq 1 and 2 eq 2
    
    1 eq 1 or 2 eq 3
    
  • The following expression may return either false or raise a dynamic error:

    1 eq 2 and 3 idiv 0 = 1
    
  • The following expression may return either true or raise a dynamic error:

    1 eq 1 or 3 idiv 0 = 1
    
  • The following expression must raise a dynamic error:

    1 eq 1 and 3 idiv 0 = 1
    

In addition to and- and or-expressions, XQuery provides a function named fn:not that takes a general sequence as parameter and returns a boolean value. The fn:not function is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The fn:not function reduces its parameter to an effective boolean value. It then returns true if the effective boolean value of its parameter is false, and false if the effective boolean value of its parameter is true. If an error is encountered in finding the effective boolean value of its operand, fn:not raises the same dynamic error.

3.7 Constructors

XQuery provides constructors that can create XML structures within a query. Constructors are provided for element, attribute, document, text, comment, and processing instruction nodes. Two kinds of constructors are provided: direct constructors, which use an XML-like notation, and computed constructors, which use a notation based on enclosed expressions.

[84]    Constructor    ::=    DirectConstructor
| ComputedConstructor
[85]    DirectConstructor    ::=    DirElemConstructor
| DirCommentConstructor
| DirPIConstructor
[86]    DirElemConstructor    ::=    "<" QName DirAttributeList ("/>" | (">" DirElemContent* "</" QName S? ">"))
[91]    DirElemContent    ::=    DirectConstructor
| ElementContentChar
| CDataSection
| CommonContent
[143]    ElementContentChar    ::=    Char - [{}<&] - [{}<&]
[92]    CommonContent    ::=    PredefinedEntityRef | CharRef | "{{" | "}}" | EnclosedExpr
[97]    CDataSection    ::=    "<![CDATA[" CDataSectionContents "]]>"
[98]    CDataSectionContents    ::=    (Char* - (Char* ']]>' Char*))
[87]    DirAttributeList    ::=    (S (QName S? "=" S? DirAttributeValue)?)*
[88]    DirAttributeValue    ::=    ('"' (EscapeQuot | QuotAttrValueContent)* '"')
| ("'" (EscapeApos | AposAttrValueContent)* "'")
[89]    QuotAttrValueContent    ::=    QuotAttrContentChar
| CommonContent
[90]    AposAttrValueContent    ::=    AposAttrContentChar
| CommonContent
[144]    QuotAttrContentChar    ::=    Char - ["{}<&] - ["{}<&]
[145]    AposAttrContentChar    ::=    Char - ['{}<&] - ['{}<&]
[141]    EscapeQuot    ::=    '""'
[142]    EscapeApos    ::=    "''"
[24]    EnclosedExpr    ::=    "{" Expr "}"

This section contains a conceptual description of the semantics of various kinds of constructor expressions. An XQuery implementation is free to use any implementation technique that produces the same result as the processing steps described in this section.

3.7.1 Direct Element Constructors

An element constructor creates an element node. [Definition: A direct element constructor is a form of element constructor in which the name of the constructed element is a constant.] Direct element constructors are based on standard XML notation. For example, the following expression is a direct element constructor that creates a book element containing attributes, subelements, and text:

<book isbn="isbn-0060229357">
    <title>Harold and the Purple Crayon</title>
    <author>
        <first>Crockett</first>
        <last>Johnson</last>
    </author>
</book>

If the element name used in a direct element constructor has a namespace prefix, the namespace prefix is resolved to a namespace URI using the statically known namespaces. If the element name has no namespace prefix, it is implicitly qualified by the default element/type namespace. Note that both the statically known namespaces and the default element/type namespace may be affected by namespace declaration attributes found inside the element constructor.

In a direct element constructor, the name used in the end tag must exactly match the name used in the corresponding start tag, including its prefix or absence of a prefix.

In a direct element constructor, curly braces { } delimit enclosed expressions, distinguishing them from literal text. Enclosed expressions are evaluated and replaced by their value, whereas material outside curly braces is simply treated as literal text, as illustrated by the following example:

<example>
   <p> Here is a query. </p>
   <eg> $i//title </eg>
   <p> Here is the result of the query. </p>
   <eg>{ $i//title }</eg>
</example>

The above query might generate the following result (whitespace has been added for readability to this result and other result examples in this document):

<example>
  <p> Here is a query. </p>
  <eg> $i//title </eg>
  <p> Here is the result of the query. </p>
  <eg><title>Harold and the Purple Crayon</title></eg>
</example>

Since XQuery uses curly braces to denote enclosed expressions, some convention is needed to denote a curly brace used as an ordinary character. For this purpose, a pair of identical curly brace characters within the content of an element or attribute are interpreted by XQuery as a single curly brace character (that is, the pair "{{" represents the character "{" and the pair "}}" represents the character "}".) Alternatively, the character references &#x7b; and &#x7d; can be used to denote curly brace characters. A single left curly brace ("{") is interpreted as the beginning delimiter for an enclosed expression. A single right curly brace ("}") without a matching left curly brace is treated as a static error.[err:XP0003]

The result of an element constructor is a new element node, with its own node identity. All the attribute and descendant nodes of the new element node are also new nodes with their own identities, even if they are copies of existing nodes.

The Base URI of a constructed element node is taken from the static context. The Base URIs of the copied descendant nodes are also taken from the static context rather than by preserving their original Base URIs. If no Base URI is defined in the static context, the Base URIs of the constructed and copied nodes are set to the empty sequence.

3.7.1.1 Attributes

The start tag of a direct element constructor may contain one or more attributes. As in XML, each attribute is specified by a name and a value. In a direct element constructor, the name of each attribute is specified by a constant QName, and the value of the attribute is specified by a string of characters enclosed in single or double quotes. As in the main content of the element constructor, an attribute value may contain expressions enclosed in curly braces, which are evaluated and replaced by their value during processing of the element constructor.

If an attribute name has a namespace prefix, the prefix is resolved to a namespace URI using the statically known namespaces. If the attribute name has no namespace prefix, the attribute is in no namespace. Note that the statically known namespaces for an attribute may be affected by namespace declaration attributes that are found inside the same element constructor. If the attributes in a direct element constructor do not have distinct names, a static error is raised. [err:XQ0040]

Each attribute in a direct element constructor creates a new attribute node, with its own node identity, whose parent is the constructed element node. However, note that namespace declaration attributes (see 3.7.1.2 Namespace Declaration Attributes) do not create attribute nodes.

Conceptually, an attribute (other than a namespace declaration attribute) in a direct element constructor is processed by the following steps:

  1. Each consecutive sequence of literal characters in the attribute content is treated as a string containing those characters. Whitespace in attribute content is normalized according to the rules for "Attribute Value Normalization" in [XML 1.0] (each whitespace character is replaced by a space (#x20) character.)

  2. Predefined entity references and character references in the attribute content are expanded into their referenced strings, as described in 3.1.1 Literals.

  3. Each enclosed expression is converted to a string as follows:

    1. Atomization is applied to the value of the enclosed expression, converting it to a sequence of atomic values.

    2. If the result of atomization is an empty sequence, the result is the zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised.

    3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.

  4. Adjacent strings resulting from the above steps are concatenated with no intervening blanks. The resulting string becomes the string value of the attribute node. The attribute node is given an initial type annotation of xdt:untypedAtomic (this type annotation may change during validation of the parent element).

  • Example:

    <shoe size="7"/>
    

    The string value of the size attribute is "7".

  • Example:

    <shoe size="{7}"/>
    

    The string value of the size attribute is "7".

  • Example:

    <shoe size="{()}"/>
    

    The string value of the size attribute is the zero-length string.

  • Example:

    <chapter ref="[{1, 5 to 7, 9}]"/>
    

    The string value of the ref attribute is "[1 5 6 7 9]".

  • Example:

    <shoe size="As big as {$hat/@size}"/>
    

    The string value of the size attribute is the string "As big as ", concatenated with the string value of the node denoted by the expression $hat/@size.

3.7.1.2 Namespace Declaration Attributes

The names of a constructed element and its attributes may be qualified names that include namespace prefixes. Namespace prefixes can be bound to namespaces in the Prolog or by namespace declaration attributes. It is a static error to use a namespace prefix that has not been bound to a namespace.[err:XP0008]

[Definition: A namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix or to set the default element/type namespace for the constructed element node, including its attributes.] Syntactically, a namespace declaration attribute has the form of an attribute with namespace prefix xmlns, or with name xmlns and no namespace prefix. The value of a namespace declaration attribute must be a StringLiteral containing a valid URI, or a zero-length string; otherwise a static error is raised. [err:XQ0022][err:XQ0046] Each namespace declaration attribute is processed as follows:

  • If the name of the namespace declaration attribute has the prefix xmlns, the local part of the name is interpreted as a namespace prefix and the value of the attribute is interpreted as a namespace URI. The given prefix and URI are added to the statically known namespaces of the constructor expression (overriding any existing binding of the given prefix), and are also added as a namespace binding to the in-scope namespaces of the constructed element. If the namespace URI is a zero-length string, the following rules apply:

  • If the name of the namespace declaration attribute is xmlns with no prefix, the value of the attribute is interpreted as a namespace URI. This URI specifies the default element/type namespace of the constructor expression (overriding any existing default), and is added (with no prefix) to the in-scope namespaces of the constructed element (overriding any existing namespace binding with no prefix). If the namespace URI is a zero-length string, the default element/type namespace of the constructor expression is set to "none," and any no-prefix namespace binding is removed from the in-scope namespaces of the constructed element.

A namespace declaration attribute does not cause an attribute node to be created.

The following examples illustrate namespace declaration attributes:

  • In this element constructor, a namespace declaration attribute is used to set the default element/type namespace to http://example.org/animals:

    <cat xmlns = "http://example.org/animals">
      <breed>Persian</breed>
    </cat>
    
  • In this element constructor, namespace declaration attributes are used to bind the namespace prefixes metric and english:

    <box xmlns:metric = "http://example.org/metric/units"
         xmlns:english = "http://example.org/english/units">
      <height> <metric:meters>3</metric:meters> </height>
      <width> <english:feet>6</english:feet> </width>
      <depth> <english:inches>18</english:inches> </depth>
    </box>
    
3.7.1.3 Content

The part of a direct element constructor between the start tag and the end tag is called the content of the element constructor. This content may consist of literal text characters, nested element constructors, CdataSections, character and predefined entity references, and expressions enclosed in curly braces. In general, the value of an enclosed expression may be any sequence of nodes and/or atomic values. Enclosed expressions can be used in the content of an element constructor to compute both the content and the attributes of the constructed node.

Conceptually, the content of an element constructor is processed as follows:

  1. The content is evaluated to produce a sequence of nodes called the content sequence, as follows:

    1. Predefined entity references and character references are expanded into their referenced strings, as described in 3.1.1 Literals. Characters inside a CDataSection, including special characters such as < and &, are treated as literal characters rather than as delimiters (except for the sequence ]]>, which terminates the CDataSection).

    2. Each consecutive sequence of literal characters evaluates to a single text node containing the characters. However, if the sequence consists entirely of boundary whitespace and the Prolog does not specify xmlspace = preserve, then no text node is generated.

    3. Each nested element constructor is evaluated according to the rules in this section, resulting in a new element node.

    4. Enclosed expressions are evaluated as follows:

      1. For each adjacent sequence of one or more atomic values returned by an enclosed expression, a new text node is constructed, containing the result of casting each atomic value to a string, with a single blank character inserted between adjacent values. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised.

        Note:

        The insertion of blank characters between adjacent values applies even if one or both of the values is a zero-length string.

      2. For each node returned by an enclosed expression, a new copy is made of the given node and all nodes that have the given node as an ancestor, collectively referred to as copied nodes. The properties of the copied nodes are as follows:

        1. Each copied node receives a new node identity.

        2. The parent, children, and attributes properties of the copied nodes are set so as to preserve their inter-node relationships. For the topmost node (the node directly returned by the enclosed expression), the parent property is empty.

        3. The base-uri properties of the copied nodes are taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri properties are empty.

        4. If construction mode in the static context is strip:

          1. The type property of each copied element node is set to xdt:untyped and its nilled property is set to false.

          2. The type property of each copied attribute node is set to xdt:untypedAtomic.

          3. The string-value of each copied element and attribute node remains unchanged, and its typed-value becomes equal to its string-value as an instance of xdt:untypedAtomic.

          On the other hand, if construction mode in the static context is preserve, the type, nilled, string-value, and typed-value properties of the copied nodes are preserved.

        5. All other properties of the copied nodes, including the in-scope-namespaces of copied element nodes, are preserved.

  2. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  3. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  4. If the content sequence contains an attribute node following a node that is not an attribute node, a type error is raised.[err:XQ0024]

  5. The properties of the newly constructed element node are determined as follows:

    1. node-name is the expanded QName resulting from resolving the element name in the start tag, as described in 3.7.1 Direct Element Constructors.

    2. base-uri is taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri property is empty.

    3. parent is empty.

    4. attributes consist of all the attributes specified in the start tag as described in 3.7.1.1 Attributes, together with all the attribute nodes in the content sequence, in implementation-dependent order. If two or more of these attributes have the same name, a dynamic error is raised.[err:XQ0025]

    5. children consist of all the element, text, comment, and processing instruction nodes in the content sequence.

    6. in-scope-namespaces consist of all the namespace bindings resulting from namespace declaration attributes as described in 3.7.1.2 Namespace Declaration Attributes, and possibly additional namespace bindings as described in 3.7.4 In-scope Namespaces of a Constructed Element.

    7. The nilled property is false.

    8. The string-value property is equal to the concatenated contents of the text-node descendants in document order.

    9. The typed-value property is equal to the string-value property, as an instance of xdt:untypedAtomic.

    10. If construction mode in the static context is strip, the type property is xdt:untyped. On the other hand, if construction mode is preserve, the type value is xs:anyType.

  • Example:

    <a>{1}</a>
    

    The constructed element node has one child, a text node containing the value "1".

  • Example:

    <a>{1, 2, 3}</a>
    

    The constructed element node has one child, a text node containing the value "1 2 3".

  • Example:

    <c>{1}{2}{3}</c>
    

    The constructed element node has one child, a text node containing the value "123".

  • Example:

    <b>{1, "2", "3"}</b>
    

    The constructed element node has one child, a text node containing the value "1 2 3".

  • Example:

    <fact>I saw 8 cats.</fact>
    

    The constructed element node has one child, a text node containing the value "I saw 8 cats.".

  • Example:

    <fact>I saw {5 + 3} cats.</fact>
    

    The constructed element node has one child, a text node containing the value "I saw 8 cats.".

  • Example:

    <fact>I saw <howmany>{5 + 3}</howmany> cats.</fact>
    

    The constructed element node has three children: a text node containing "I saw ", a child element node named howmany, and a text node containing " cats.". The child element node in turn has a single text node child containing the value "8".

3.7.1.4 Whitespace in Element Content

In a direct element constructor, whitespace characters may appear in element content. In some cases, enclosed expressions and/or nested elements may be separated only by whitespace characters. For example, in the expression below, the end-tag </title> and the start-tag <author> are separated by a newline character and four space characters:

<book isbn="isbn-0060229357">
    <title>Harold and the Purple Crayon</title>
    <author>
        <first>Crockett</first>
        <last>Johnson</last>
    </author>
</book>

[Definition: Whitespace characters that occur by themselves in the boundaries between tags and/or enclosed expressions are called boundary whitespace.] The Prolog contains a declaration called xmlspace that controls whether boundary whitespace is preserved by direct element constructors. If xmlspace is not declared in the prolog or is declared as xmlspace = strip, boundary whitespace is not considered significant and is discarded. On the other hand, if xmlspace = preserve is declared in the prolog, boundary whitespace is considered significant and is preserved.

  • Example:

    <cat> 
       <breed>{$b}</breed>
       <color>{$c}</color> 
    </cat>
    

    The constructed cat element node has two child element nodes named breed and color. Whitespace surrounding the child elements has been stripped away by the element constructor (assuming that the Prolog did not specify xmlspace = preserve.)

  • Example:

    <a>  {"abc"}  </a>
    

    If xmlspace is not declared or is declared as xmlspace = strip, this example is equivalent to <a>abc</a>. However, if xmlspace = preserve is declared, this example is equivalent to <a>  abc  </a>.

  • Example:

    <a> z {"abc"}</a>
    

    Since the whitespace surrounding the z is not boundary whitespace, it is always preserved. This example is equivalent to <a> z abc</a>.

For the purpose of the above rule, whitespace characters generated by character references such as &#x20; or by CdataSections are not considered to be boundary whitespace, and are always preserved. Similarly, whitespace characters that are adjacent to a character reference or a CDataSection are always preserved.

  • Example:

    <a>&#x20;{"abc"}</a>
    

    This example is equivalent to <a> abc</a>, regardless of the declaration of xmlspace.

It is important to remember that whitespace generated by an enclosed expression is never considered to be boundary whitespace, and is always preserved.

  • Example:

    <a>{"  "}</a>
    

    This example is equivalent to <a>  </a>, regardless of the declaration of xmlspace.

3.7.2 Other Direct Constructors

XQuery allows a query to generate a processing instruction or XML comment directly into the query result. In each case, this is accomplished by using a constructor expression whose syntax is based on the syntax of the equivalent construct in XML.

[95]    DirPIConstructor    ::=    "<?" PITarget (S DirPIContents)? "?>"
[96]    DirPIContents    ::=    (Char* - (Char* '?>' Char*))
[93]    DirCommentConstructor    ::=    "<!--" DirCommentContents "-->"
[94]    DirCommentContents    ::=    ((Char - '-') | ('-' (Char - '-')))*

The content of a processing instruction may not contain the string "?>", and the content of a comment may not contain two consecutive hyphens or end with a hyphen. These rules are enforced by the grammar shown above.

The following example illustrates a constructed processing instruction:

<?format role="output" ?>

The following example illustrates a constructed XML comment:

<!-- Tags are ignored in the following section -->

Note that an XML comment constructor actually constructs a comment node in the data model. An XQuery comment, on the other hand, (see 2.7 Comments) is simply a comment used in documenting a query, and is not evaluated. Consider the following example.

(: This is an XQuery comment :)
<!-- This is an XML comment -->

The result of evaluating the above expression is as follows.

<!-- This is an XML comment -->

3.7.3 Computed Constructors

[99]    ComputedConstructor    ::=    CompDocConstructor
| CompElemConstructor
| CompAttrConstructor
| CompTextConstructor
| CompCommentConstructor
| CompPIConstructor

An alternative way to create nodes is by using a computed constructor. A computed constructor begins with a keyword that identifies the type of node to be created: element, attribute, document, text, processing-instruction, or comment.

For those kinds of nodes that have names (element, attribute, and processing instruction nodes), the keyword that specifies the node kind is followed by the name of the node to be created. This name may be specified either as a QName or as an expression enclosed in braces, called the name expression, that returns a string or a QName.

The final part of a computed constructor is an expression enclosed in braces, called the content expression, that generates the content of the node.

The following example illustrates the use of computed element and attribute constructors in a simple case where the names of the constructed nodes are constants. This example generates exactly the same result as the first example in 3.7.1 Direct Element Constructors:

element book { 
   attribute isbn {"isbn-0060229357" }, 
   element title { "Harold and the Purple Crayon"},
   element author { 
      element first { "Crockett" }, 
      element last {"Johnson" }
   }
}
3.7.3.1 Computed Element Constructors
[101]    CompElemConstructor    ::=    (("element" QName "{") | ("element" "{" Expr "}" "{")) CompElemBody? "}"
[102]    CompElemBody    ::=    (LocalNamespaceDecl | ExprSingle) ("," (LocalNamespaceDecl | ExprSingle))*
[103]    LocalNamespaceDecl    ::=    "namespace" NCName? "{" StringLiteral "}"

[Definition: A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.]

The name expression of a computed element constructor is processed as follows:

  1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic value of type xs:QName, xs:string, or xdt:untypedAtomic, a type error is raised.[err:XP0004][err:XP0006]

  2. If the atomized value of the name expression is of type xs:QName, that expanded QName is used as the name of the constructed element.

  3. If the atomized value of the name expression is of type xs:string or xdt:untypedAtomic, that value is converted to an expanded QName. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the statically known namespaces. If the string value contains no namespace prefix, it is treated as a local name in the default element/type namespace. Note that both the statically known namespaces and the default element/type namespace may be affected by local namespace declarations found inside the computed element constructor.

In a computed element constructor, the name expression is followed by the body, which consists of zero or more local namespace declarations (LocalNamespaceDecl) followed an optional content expression (ExprSingle). If more than one content expression is present, or if a local namespace declaration follows the content expression, a static error is raised.[err:XQ0042]

[Definition: A local namespace declaration in a computed element constructor contains an optional namespace prefix and a namespace URI expressed as a string literal.] Each local namespace declaration is processed as follows:

If two or more local namespace declarations in the same computed element constructor have the same prefix or have no prefix, a static error is raised. [err:XQ0043] The use of local namespace declarations in a computed element constructor is illustrated by the following example, in which the default element/type namespace is set to http://example.org/ns1 and the prefix space2 is bound to the namespace URI http://example.org/ns2:

element {$computed-name}
   {
   namespace {"http://example.org/ns1"},
   namespace space2 {"http://example.org/ns2"},
   $content
   }

The content expression of a computed element constructor is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1d of 3.7.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. Processing of the computed element constructor then proceeds as follows:

  1. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  2. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  3. If the content sequence contains an attribute node following a node that is not an attribute node, a type error is raised.[err:XQ0024]

  4. The properties of the newly constructed element node are determined as follows:

    1. node-name is the expanded QName resulting from processing the name expression, as described above.

    2. base-uri is taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri property is empty.

    3. parent is empty.

    4. attributes consist of all the attribute nodes in the content sequence, in implementation-dependent order. If two or more of these attributes have the same name, a dynamic error is raised.[err:XQ0025]

    5. children consist of all the element, text, comment, and processing instruction nodes in the content sequence.

    6. in-scope-namespaces consist of all the namespace bindings resulting from local namespace declarations, as described above, and possibly additional namespace bindings as described in 3.7.4 In-scope Namespaces of a Constructed Element.

    7. The nilled property is false.

    8. The string-value property is equal to the concatenated contents of the text-node descendants in document order.

    9. The typed-value property is equal to the string-value property, as an instance of xdt:untypedAtomic.

    10. If construction mode in the static context is strip, the type property is xdt:untyped. On the other hand, if construction mode is preserve, the type value is xs:anyType.

A computed element constructor might be used to make a modified copy of an existing element. For example, if the variable $e is bound to an element with numeric content, the following constructor might be used to create a new element with the same name and attributes as $e and with numeric content equal to twice the value of $e:

element {fn:node-name($e)}
   {$e/@*, 2 * fn:data($e)}

In this example, if $e is bound by the expression let $e := <length units="inches">{5}</length>, then the result of the example expression is the element <length units="inches">10</length>.

Note:

The static type of the expression fn:node-name($e) is xs:QName?, denoting zero or one QName. Therefore, if the Static Typing Feature is in effect, the above example raises a static type error, since the name expression in a computed element constructor is required to return exactly one string or QName. In order to avoid the static type error, the name expression fn:node-name($e) could be rewritten as fn:exactly-one(fn:node-name($e)). If the Static Typing Feature is not in effect, the example can be successfully evaluated as written, provided that $e is bound to exactly one element node with numeric content.

One important purpose of computed constructors is to allow the name of a node to be computed. We will illustrate this feature by an expression that translates the name of an element from one language to another. Suppose that the variable $dict is bound to a sequence of entries in a translation dictionary. Here is an example entry:

<entry word="address">
   <variant lang="German">Adresse</variant>
   <variant lang="Italian">indirizzo</variant>
</entry> 

Suppose further that the variable $e is bound to the following element:

<address>123 Roosevelt Ave. Flushing, NY 11368</address>

Then the following expression generates a new element in which the name of $e has been translated into Italian and the content of $e (including its attributes, if any) has been preserved. The first enclosed expression after the element keyword generates the name of the element, and the second enclosed expression generates the content and attributes:

  element 
    {$dict/entry[word=name($e)]/variant[lang="Italian"]}
    {$e/@*, $e/*}

The result of this expression is as follows:

<indirizzo>123 Roosevelt Ave. Flushing, NY 11368</indirizzo>

Note:

As in the previous example, if the Static Typing Feature is in effect, the enclosed expression that computes the element name in the above computed element constructor must be wrapped in a call to the fn:exactly-one function in order to avoid a static type error.

Additional examples of computed element constructors can be found in G.4 Recursive Transformations.

3.7.3.2 Computed Attribute Constructors
[104]    CompAttrConstructor    ::=    (("attribute" QName "{") | ("attribute" "{" Expr "}" "{")) Expr? "}"

A computed attribute constructor creates a new attribute node, with its own node identity.

The name expression of a computed attribute constructor is processed as follows:

  1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic value of type xs:QName, xs:string, or xdt:untypedAtomic, a type error is raised.[err:XP0004][err:XP0006]

  2. If the atomized value of the name expression is of type xs:QName, that expanded QName is used as the name of the constructed attribute.

  3. If the atomized value of the name expression is of type xs:string or xdt:untypedAtomic, that value is converted to an expanded QName. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the statically known namespaces. If the string value contains no namespace prefix, it is treated as a local name in no namespace. Note that the statically known namespaces for a constructed attribute may be affected by local namespace declarations found in an enclosing element constructor. The resulting expanded QName is used as the name of the constructed attribute.

  4. A dynamic error [err:XQ0044] is raised if the URI part of the resulting QName is http://www.w3.org/TR/REC-xml-names (corresponding to namespace prefix xmlns) or if the resulting QName is in no namespace and has local name xmlns.

The content expression of a computed attribute constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.

  2. If the result of atomization is an empty sequence, the value of the attribute is the zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string is the string value of the new attribute node. The type property of the new attribute node is xdt:untypedAtomic. Its parent property is empty.

  • Example:

    attribute size {4 + 3}
    

    The value of the size attribute is "7".

  • Example:

    attribute
       { if ($sex = "M") then "husband" else "wife" }
       { <a>Hello</a>, 1 to 3, <b>Goodbye</b> }
    

    The name of the constructed attribute is either husband or wife. Its string value is "Hello 1 2 3 Goodbye".

3.7.3.3 Document Node Constructors
[100]    CompDocConstructor    ::=    "document" "{" Expr "}"

All document node constructors are computed constructors. The result of a document node constructor is a new document node, with its own node identity.

A document node constructor is useful when the result of a query is to be a document in its own right. The following example illustrates a query that returns an XML document containing a root element named author-list:

document
   {
      <author-list>
         {fn:doc("bib.xml")//book/author}
      </author-list>
   }

The content expression of a document node constructor is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1d of 3.7.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. Processing of the document node constructor then proceeds as follows:

  1. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  2. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  3. If the content sequence contains an attribute node, a type error is raised.[err:XP0004][err:XP0006]

  4. The properties of the newly constructed document node are determined as follows:

    1. base-uri is taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri property is empty.

    2. children consist of all the element, text, comment, and processing instruction nodes in the content sequence.

    3. The unparsed-entities and document-uri properties are empty.

    4. The string-value and typed-value properties are derived from the children property as described in [XQuery 1.0 and XPath 2.0 Data Model].

No validation is performed on the constructed document node. The [XML 1.0] rules that govern the structure of an XML document (for example, the document node must have exactly one child that is an element node) are not enforced by the XQuery document node constructor.

3.7.3.4 Text Node Constructors
[105]    CompTextConstructor    ::=    "text" "{" Expr "}"

All text node constructors are computed constructors. The result of a text node constructor is a new text node, with its own node identity.

The content expression of a text node constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.

  2. If the result of atomization is an empty sequence, no text node is constructed. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the content of the constructed text node.

Note:

It is possible for a text node constructor to construct a text node containing a zero-length string. However, if used in the content of a constructed element or document node, such a text node will be deleted or merged with another text node.

The following example illustrates a text node constructor:

text {"Hello"}
3.7.3.5 Computed Processing Instruction Constructors
[107]    CompPIConstructor    ::=    (("processing-instruction" NCName "{") | ("processing-instruction" "{" Expr "}" "{")) Expr? "}"

A computed processing instruction constructor (CompPIConstructor) constructs a new processing instruction node with its own node identity. The name expression of a computed processing instruction constructor is processed as follows:

  1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic value of type xs:NCName, xs:string, or xdt:untypedAtomic, a type error is raised.[err:XP0004][err:XP0006]

  2. If the atomized value of the name expression is of type xs:string or xdt:untypedAtomic, that value is cast to the type xs:NCName. If the value cannot be cast to xs:NCName, a dynamic error is raised.[err:XQ0041]

  3. The resulting NCName is then used as the name (target) of the newly constructed processing instruction node. However, a dynamic error is raised if the NCName is equal to "XML" (in any combination of upper and lower case) [err:XQ0064] or if it contains the string "?>" [err:XQ0026].

The content expression of a computed processing instruction constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.

  2. If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised. If any of the resulting strings contains the string "?>", a dynamic error [err:XQ0026] is raised.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the content of the constructed processing instruction node.

The following expression contains an example of a computed processing instruction constructor. The result of the expression is a processing instruction node.

let $target := "audio-output",
    $content := "beep" 
return processing-instruction {$target} {$content}
3.7.3.6 Computed Comment Constructors
[106]    CompCommentConstructor    ::=    "comment" "{" Expr "}"

A computed comment constructor (CompCommentConstructor) constructs a new comment node with its own node identity. The content expression of a computed comment constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.

  2. If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.

  4. For each pair of adjacent hyphens in the resulting string, one blank character is inserted between the adjacent hyphens. If the resulting string ends with a hyphen, one blank character is added to the end of the string. The resulting string then becomes the content of the constructed comment.

The following query contains an example of a computed comment constructor. The result of the query is a comment node.

let $homebase := "Houston" 
return comment {fn:concat($homebase, ", we have a problem.")}

3.7.4 In-scope Namespaces of a Constructed Element

An element node constructed by a direct or computed element constructor has an in-scope namespaces property that consists of a set of namespace bindings. The in-scope namespaces of an element node may affect the way the node is serialized (see 2.2.4 Serialization), and may also affect the behavior of certain functions that operate on nodes, such as fn:name. Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression. Also note that one of the namespace bindings in the in-scope namespaces may have no prefix (denoting the default namespace for the given element). The in-scope namespaces of a constructed element node consist of the following namespace bindings:

  • A namespace binding is created for each namespace declared in the current element constructor by a namespace declaration attribute or a local namespace declaration.

  • A namespace binding is created for each namespace that is declared in an ancestor element constructor and not overridden by the current element constructor or a lower-level ancestor. For this purpose, namespace declarations include both namespace declaration attributes and local namespace declarations.

  • A namespace binding is always created to bind the prefix xml to the namespace URI http://www.w3.org/XML/1998/namespace.

  • For each namespace used in the name of the constructed element or in the names of its attributes, a namespace binding must exist. If a namespace binding does not already exist for one of these namespaces, a new namespace binding is created for it, using an implementation-dependent prefix that does not conflict with any other prefix in the in-scope namespaces of the constructed element.

    Note:

    Implementations may in many cases be able to choose a namespace prefix that is familiar to the user, such as a prefix that is associated with the corresponding namespace URI in either the source document or the query. In some cases, for example to avoid duplicate declarations of the same prefix, an arbitrary choice must be made.

The following query serves as an example:

declare namespace p="http://example.com/ns/p";
declare namespace q="http://example.com/ns/q";
declare namespace f="http://example.com/ns/f";

<p:a q:b="{f:func(2)}" xmlns:r="http://example.com/ns/r"/>

The in-scope namespaces of the resulting p:a element consists of the following namespace bindings:

  • NS0="http://example.com/ns/p"

  • NS1="http://example.com/ns/q"

  • r="http://example.com/ns/r"

  • xml="http://www.w3.org/XML/1998/namespace"

Here NS0 and NS1 represent namespace prefixes. These namespace bindings are added to the result element because their respective namespaces are used in the names of the element and its attributes; the namespace prefixes are therefore implementation-dependent. The implementation might use the prefixes p and q respectively, but it is not required to do so.

The namespace binding r="http://example.com/ns/r" is added to the in-scope namespaces of the constructed element because it is defined by a namespace declaration attribute, even though it is not used in a name.

No namespace binding corresponding to f="http://example.com/ns/f" is created, because the namespace prefix f appears only in the query prolog and is not used in an element or attribute name of the constructed node. This namespace binding does not appear in the query result, even though it is present in the statically known namespaces and is available for use during processing of the query.

Note that the following constructed element cannot be validated:

<p xsi:type="xs:integer">3</p>

The constructed element will have namespace bindings for the prefixes xsi (because it is used in a name) and xml (because it is defined for every constructed element node). During validation of the constructed element, the validator will be unable to interpret the namespace prefix xs because it is has no namespace binding.

3.8 FLWOR Expressions

XQuery provides a feature called a FLWOR expression that supports iteration and binding of variables to intermediate results. This kind of expression is often useful for computing joins between two or more documents and for restructuring data. The name FLWOR, pronounced "flower", is suggested by the keywords for, let, where, order by, and return.

[28]    FLWORExpr    ::=    (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle
[29]    ForClause    ::=    "for" "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle)*
[31]    LetClause    ::=    "let" "$" VarName TypeDeclaration? ":=" ExprSingle ("," "$" VarName TypeDeclaration? ":=" ExprSingle)*
[109]    TypeDeclaration    ::=    "as" SequenceType
[30]    PositionalVar    ::=    "at" "$" VarName
[32]    WhereClause    ::=    "where" Expr
[33]    OrderByClause    ::=    ("order" "by" | "stable" "order" "by") OrderSpecList
[34]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[35]    OrderSpec    ::=    ExprSingle OrderModifier
[36]    OrderModifier    ::=    ("ascending" | "descending")? (("empty" "greatest") | ("empty" "least"))? ("collation" StringLiteral)?

The for and let clauses in a FLWOR expression generate an ordered sequence of tuples of bound variables, called the tuple stream. The optional where clause serves to filter the tuple stream, retaining some tuples and discarding others. The optional order by clause can be used to reorder the tuple stream. The return clause constructs the result of the FLWOR expression. The return clause is evaluated once for every tuple in the tuple stream, after filtering by the where clause, using the variable bindings in the respective tuples. The result of the FLWOR expression is an ordered sequence containing the concatenated results of these evaluations.

The following example of a FLWOR expression includes all of the possible clauses. The for clause iterates over all the departments in an input document, binding the variable $d to each department number in turn. For each binding of $d, the let clause binds variable $e to all the employees in the given department, selected from another input document. The result of the for and let clauses is a tuple stream in which each tuple contains a pair of bindings for $d and $e ($d is bound to a department number and $e is bound to a set of employees in that department). The where clause filters the tuple stream by keeping only those binding-pairs that represent departments having at least ten employees. The order by clause orders the surviving tuples in descending order by the average salary of the employees in the department. The return clause constructs a new big-dept element for each surviving tuple, containing the department number, headcount, and average salary.

for $d in fn:doc("depts.xml")//deptno
let $e := fn:doc("emps.xml")//emp[deptno = $d]
where fn:count($e) >= 10
order by fn:avg($e/salary) descending
return
   <big-dept>
      {
      $d,
      <headcount>{fn:count($e)}</headcount>,
      <avgsal>{fn:avg($e/salary)}</avgsal>
      }
   </big-dept>

The clauses in a FLWOR expression are described in more detail below.

3.8.1 For and Let Clauses

The purpose of the for and let clauses in a FLWOR expression is to produce a tuple stream in which each tuple consists of one or more bound variables.

The simplest example of a for clause contains one variable and an associated expression. We will refer to the value of the expression as the input sequence. The for clause iterates over the items in the input sequence, binding the variable to each item in turn. If ordering mode is ordered, the resulting sequence of variable bindings is ordered according to the order of values in the input sequence; otherwise the ordering of the variable bindings is implementation-dependent.

A for clause may also contain multiple variables, each with an associated expression whose value is the input sequence for that variable. In this case, the for clause iterates each variable over its input sequence. The resulting tuple stream contains one tuple for each combination of values in the Cartesian product of the input sequences. If ordering mode is ordered, the order of the tuple stream is determined primarily by the order of the input sequence of the leftmost variable, and secondarily by the input sequences of the other variables, working from left to right. Otherwise, the ordering of the variable bindings is implementation-dependent.

A let clause may also contain one or more variables, each with an associated expression. Unlike a for clause, however, a let clause binds each variable to the result of its associated expression, without iteration. The variable bindings generated by let clauses are added to the binding tuples generated by the for clauses. If there are no for clauses, the let clauses generate one tuple containing all the variable bindings.

Although for and let clauses both bind variables, the manner in which variables are bound is quite different, as illustrated by the following examples. The first example uses a let clause:

let $s := (<one/>, <two/>, <three/>)
return <out>{$s}</out>

The variable $s is bound to the result of the expression (<one/>, <two/>, <three/>). Since there are no for clauses, the let clause generates one tuple that contains the binding of $s. The return clause is invoked for this tuple, creating the following output:

<out>
   <one/>
   <two/>
   <three/>
</out>

The next example is a similar query that contains a for clause instead of a let clause:

for $s in (<one/>, <two/>, <three/>)
return <out>{$s}</out>

In this example, the variable $s iterates over the given expression. If ordering mode is ordered, $s is first bound to <one/>, then to <two/>, and finally to <three/>. One tuple is generated for each of these bindings, and the return clause is invoked for each tuple, creating the following output:

<out>
   <one/>
</out>
<out>
   <two/>
</out>
<out>
   <three/>
</out>

The following example illustrates how binding tuples are generated by a for clause that contains multiple variables when ordering mode is ordered.

for $i in (1, 2), $j in (3, 4)

The tuple stream generated by the above for clause is as follows:

($i = 1, $j = 3)
($i = 1, $j = 4)
($i = 2, $j = 3)
($i = 2, $j = 4)

If ordering mode were unordered, the for clause in the above example would generate the same tuple stream but the order of the tuples would be implementation-dependent.

The scope of a variable bound in a for or let clause comprises all subexpressions of the containing FLWOR expression that appear after the variable binding. The scope does not include the expression to which the variable is bound. The following example illustrates how for and let clauses may reference variables that were bound in earlier clauses in the same FLWOR expression:

for $x in $w
let $y := f($x)
for $z in g($x, $y)
return h($x, $y, $z)

Each variable bound in a for or let clause may have an optional type declaration, which is a type declared using the syntax in 2.4.3 SequenceType Syntax. If the type of a value bound to the variable does not match the declared type according to the rules for SequenceType matching, a type error is raised.[err:XP0004][err:XP0006] For example, the following expression raises a type error because the variable $salary has a type declaration that is not satisfied by the value that is bound to the variable:

let $salary as xs:decimal :=  "cat"
return $salary * 2

Each variable bound in a for clause may have an associated positional variable that is bound at the same time. The name of the positional variable is preceded by the keyword at. The positional variable always has an implied type of xs:integer. As a variable iterates over the items in its input sequence, its positional variable iterates over the integers that represent the ordinal positions of those items in the input sequence, starting with 1.

Positional variables are illustrated by the following for clause:

for $car at $i in ("Ford", "Chevy"),
    $pet at $j in ("Cat", "Dog")

If ordering mode is ordered, the tuple stream generated by the above for clause is as follows:

($i = 1, $car = "Ford", $j = 1, $pet = "Cat")
($i = 1, $car = "Ford", $j = 2, $pet = "Dog")
($i = 2, $car = "Chevy", $j = 1, $pet = "Cat")
($i = 2, $car = "Chevy", $j = 2, $pet = "Dog")

If ordering mode is unordered, the resulting tuple stream contains the same tuples, in implementation-dependent order.

3.8.2 Where Clause

The optional where clause serves as a filter for the tuples of variable bindings generated by the for and let clauses. The expression in the where clause, called the where-expression, is evaluated once for each of these tuples. If the effective boolean value of the where-expression is true, the tuple is retained and its variable bindings are used in an execution of the return clause. If the effective boolean value of the where-expression is false, the tuple is discarded. The effective boolean value of an expression is defined in 2.3.3 Effective Boolean Value.

The following expression illustrates how a where clause might be applied to a positional variable in order to perform sampling on an input sequence. This expression approximates the average value in a sequence by sampling one value out of each one hundred input values.

fn:avg(for $x at $i in $inputvalues
    where $i mod 100 = 0   
    return $x)

3.8.3 Order By and Return Clauses

The return clause of a FLWOR expression is evaluated once for each tuple in the tuple stream, and the results of these evaluations are concatenated to form the result of the FLWOR expression.

If no order by clause is present, the order of the tuple stream is determined by the for and let clauses and by ordering mode. If an order by clause is present, it reorders the tuples in the tuple stream into a new, value-based order. In either case, the resulting order determines the order in which the return clause is evaluated, once for each tuple, using the variable bindings in the respective tuples. Note that ordering mode has no effect on a FLWOR expression if an order by clause is present, since order by takes precedence over ordering mode.

An order by clause contains one or more ordering specifications, called orderspecs, as shown in the grammar above. For each tuple in the tuple stream, the orderspecs are evaluated, using the variable bindings in that tuple. The relative order of two tuples is determined by comparing the values of their orderspecs, working from left to right until a pair of unequal values is encountered. If the values to be compared are strings, the orderspec may indicate the collation to be used (if no collation is specified, the default collation is used.)

The process of evaluating and comparing the orderspecs is based on the following rules:

  • Atomization is applied to the result of the expression in each orderspec. If the result of atomization is neither a single atomic value nor an empty sequence, a type error is raised.[err:XP0004][err:XP0006]

  • If the value of an orderspec has the dynamic type xdt:untypedAtomic (such as character data in a schemaless document), it is cast to the type xs:string.

    Note:

    Consistently treating untyped values as strings enables the sorting process to begin without complete knowledge of the types of all the values to be sorted.

  • All the orderspec values must be convertible to a common type by subtype substitution and/or numeric type promotion. The ordering is performed in the least common type that has a gt operator. If two or more orderspec values are not convertible to a common type that has a gt operator, a type error is raised. [err:XP0004][err:XP0006]

    • Example: The orderspec values include a value of type hatsize, which is derived from xs:integer, and a value of type shoesize, which is derived from xs:decimal. The least common type reachable by subtype substitution and numeric type promotion is xs:decimal.

    • Example: The orderspec values include a value of type xs:string and a value of type xs:anyURI. Since these types have no common type reachable by subtype substitution and numeric type promotion, a type error is raised.

When two orderspec values are compared to determine their relative position in the ordering sequence, the greater-than relationship is defined as follows:

  • When the orderspec specifies empty least, a value W is considered to be greater-than a value V if one of the following is true:

    • V is an empty sequence and W is not an empty sequence.

    • V is NaN, and W is neither NaN nor an empty sequence.

    • No collation is specified, and W gt V is true.

    • A specific collation C is specified, and fn:compare(V, W, C) is less than zero.

  • When the orderspec specifies empty greatest, a value W is considered to be greater-than a value V if one of the following is true:

    • W is an empty sequence and V is not an empty sequence.

    • W is NaN, and V is neither NaN nor an empty sequence.

    • No collation is specified, and W gt V is true.

    • A specific collation C is specified, and fn:compare(V, W, C) is less than zero.

  • When the orderspec specifies neither empty least nor empty greatest, it is implementation-defined whether the rules for empty least or empty greatest are used.

If T1 and T2 are two tuples in the tuple stream, and V1 and V2 are the first pair of values encountered when evaluating their orderspecs from left to right for which one value is greater-than the other (as defined above), then:

  1. If V1 is greater-than V2: If the orderspec specifies descending, then T1 precedes T2 in the tuple stream; otherwise, T2 precedes T1 in the tuple stream.

  2. If V2 is greater-than V1: If the orderspec specifies descending, then T2 precedes T1 in the tuple stream; otherwise, T1 precedes T2 in the tuple stream.

If neither V1 nor V2 is greater-than the other for any pair of orderspecs for tuples T1 and T2, then:

  1. If stable is specified, the original order of T1 and T2 is preserved in the tuple stream.

  2. If stable is not specified, the order of T1 and T2 in the tuple stream is implementation-dependent.

An order by clause makes it easy to sort the result of a FLWOR expression, even if the sort key is not included in the result of the expression. For example, the following expression returns employee names in descending order by salary, without returning the actual salaries:

for $e in $employees 
order by $e/salary descending 
return $e/name

The order by clause is the only facility provided by XQuery for specifying an order other than document order. Therefore, every query in which an order other than document order is required must contain a FLWOR expression, even though iteration would not otherwise be necessary. For example, a list of books with price less than 100 might be obtained by a simple path expression such as $books//book[price < 100]. But if these books are to be returned in alphabetic order by title, the query must be expressed as follows:

for $b in $books//book[price < 100]
order by $b/title
return $b

The following example illustrates an order by clause that uses several options. It causes a collection of books to be sorted in primary order by title, and in secondary descending order by price. A specific collation is specified for the title ordering, and in the ordering by price, books with no price are specified to occur last (as though they have the least possible price). Whenever two books with the same title and price occur, the keyword stable indicates that their input order is preserved.

for $b in $books//book
stable order by $b/title collation "eng-us",
   $b/price descending empty least
return $b

3.8.4 Example

The following example illustrates how FLWOR expressions can be nested, and how ordering can be specified at multiple levels of an element hierarchy. The example query inverts a document hierarchy to transform a bibliography into an author list. The input bibliography is a list of books in which each book contains a list of authors. The example is based on the following input:

<bib>
  <book>
    <title>TCP/IP Illustrated</title>
    <author>Stevens</author>
    <publisher>Addison-Wesley</publisher>
  </book>
  <book>
    <title>Advanced Programming
           in the Unix Environment</title>
    <author>Stevens</author>
    <publisher>Addison-Wesley</publisher>
  </book>
  <book>
    <title>Data on the Web</title>
    <author>Abiteboul</author>
    <author>Buneman</author>
    <author>Suciu</author>
  </book>
</bib>

The following query transforms the input document into a list in which each author's name appears only once, followed by a list of titles of books written by that author. The fn:distinct-values function is used to eliminate duplicates (by value) from a list of author nodes. The author list, and the lists of books published by each author, are returned in alphabetic order using the default collation.

<authlist>
 {
   for $a in fn:distinct-values($books//author)
   order by $a
   return
     <author>
        <name> {$a} </name>
        <books>
          {
            for $b in $books//book[author = $a]
            order by $b/title
            return $b/title 
          }
        </books>
     </author>
 }
</authlist>

The result of the above expression is as follows:

<authlist>
   <author>
      <name>Abiteboul</name>
      <books>
         <title>Data on the Web</title>
      </books>
   </author>
   <author>
      <name>Buneman</name>
      <books>
         <title>Data on the Web</title>
      </books>
   </author>
   <author>
      <name>Stevens</name>
      <books>
         <title>TCP/IP Illustrated</title>
         <title>Advanced Programming
                in the Unix Environment</title>
      </books>
   </author>
   <author>
      <name>Suciu</name>
      <books>
         <title>Data on the Web</title>
      </books>
   </author>
</authlist>

3.9 Ordered and Unordered Expressions

[81]    OrderedExpr    ::=    "ordered" "{" Expr "}"
[82]    UnorderedExpr    ::=    "unordered" "{" Expr "}"

The purpose of ordered and unordered expressions is to set the ordering mode in the static context to ordered or unordered for a certain region in a query. The specified ordering mode applies to the expression nested inside the curly braces. For expressions where the ordering of the result is not significant, a performance advantage may be realized by setting the ordering mode to unordered, thereby granting the system flexibility to return the result in the order that it finds most efficient.

Ordering mode affects the behavior of path expressions, union, intersect, and except expressions, and FLWOR expressions that have no order by clause. If ordering mode is ordered, node sequences returned by path, union, intersect, and except expressions are in document order; otherwise the order of these return sequences is implementation-dependent. The effect of ordering mode on FLWOR expressions is described in 3.8 FLWOR Expressions. Ordering mode has no effect on duplicate elimination.

Note:

In a region of the query where ordering mode is unordered, certain functions that depend on the ordering of node sequences may return nondeterministic results. These functions include fn:position, fn:last, fn:index-of, fn:insert-before, fn:remove, fn:reverse, and fn:subsequence. Also, within a path expression in an unordered region, numeric predicates are nondeterministic. For example, in an ordered region, the path expression //a/b[5] will return the fifth qualifying b-element in document order. In an unordered region, the same expression will return an implementation-dependent qualifying b-element.

The use of an unordered expression is illustrated by the following example, which joins together two documents named parts.xml and suppliers.xml. The example returns the part numbers of red parts, paired with the supplier numbers of suppliers who supply these parts. If an unordered expression were not used, the resulting list of (part number, supplier number) pairs would be required to have an ordering that is controlled primarily by the document order of parts.xml and secondarily by the document order of suppliers.xml. However, this might not be the most efficient way to process the query if the ordering of the result is not important. An XQuery implementation might be able to process the query more efficiently by using an index to find the red parts, or by using suppliers.xml rather than parts.xml to control the primary ordering of the result. The unordered expression gives the query evaluator freedom to make these kinds of optimizations.

unordered {
  for $p in fn:doc("parts.xml")//part[color = "Red"],
      $s in fn:doc("suppliers.xml")//supplier
  where $p/suppno = $s/suppno  
  return
    <ps>
       { $p/partno, $s/suppno }
    </ps>
}

In addition to ordered and unordered expressions, XQuery provides a function named fn:unordered that operates on any sequence of items and returns the same sequence in a nondeterministic order. A call to the fn:unordered function may be thought of as giving permission for the argument expression to be materialized in whatever order the system finds most efficient. The fn:unordered function differs from an unordered expression in the following ways:

  • The fn:unordered function relaxes ordering only for the sequence that is its immediate operand, whereas an unordered expression sets the ordering mode for its operand expression and all nested expressions.

  • The fn:unordered function can operate on any sequence, whereas an unordered expression affects the ordering only of node sequences (not sequences of atomic values).

3.10 Conditional Expressions

XQuery supports a conditional expression based on the keywords if, then, and else.

[40]    IfExpr    ::=    "if" "(" Expr ")" "then" ExprSingle "else" ExprSingle

The expression following the if keyword is called the test expression, and the expressions following the then and else keywords are called the then-expression and else-expression, respectively.

The first step in processing a conditional expression is to find the effective boolean value of the test expression, as defined in 2.3.3 Effective Boolean Value.

The value of a conditional expression is defined as follows: If the effective boolean value of the test expression is true, the value of the then-expression is returned. If the effective boolean value of the test expression is false, the value of the else-expression is returned.

Conditional expressions have a special rule for propagating dynamic errors. If the effective value of the test expression is true, the conditional expression ignores (does not raise) any dynamic errors encountered in the else-expression. In this case, since the else-expression can have no observable effect, it need not be evaluated. Similarly, if the effective value of the test expression is false, the conditional expression ignores any dynamic errors encountered in the then-expression, and the then-expression need not be evaluated.

Here are some examples of conditional expressions:

  • In this example, the test expression is a comparison expression:

    if ($widget1/unit-cost < $widget2/unit-cost) 
      then $widget1
      else $widget2
    
  • In this example, the test expression tests for the existence of an attribute named discounted, independently of its value:

    if ($part/@discounted) 
      then $part/wholesale 
      else $part/retail
    

3.11 Quantified Expressions

Quantified expressions support existential and universal quantification. The value of a quantified expression is always true or false.

[37]    QuantifiedExpr    ::=    (("some" "$") | ("every" "$")) VarName TypeDeclaration? "in" ExprSingle ("," "$" VarName TypeDeclaration? "in" ExprSingle)* "satisfies" ExprSingle

A quantified expression begins with a quantifier, which is the keyword some or every, followed by one or more in-clauses that are used to bind variables, followed by the keyword satisfies and a test expression. Each in-clause associates a variable with an expression that returns a sequence of values. The in-clauses generate tuples of variable bindings, using values drawn from the Cartesian product of the sequences returned by the binding expressions. Conceptually, the test expression is evaluated for each tuple of variable bindings. Results depend on the effective boolean values of the test expressions, as defined in 2.3.3 Effective Boolean Value. The value of the quantified expression is defined by the following rules:

  1. If the quantifier is some, the quantified expression is true if at least one evaluation of the test expression has the effective boolean value true; otherwise the quantified expression is false. This rule implies that, if the in-clauses generate zero binding tuples, the value of the quantified expression is false.

  2. If the quantifier is every, the quantified expression is true if every evaluation of the test expression has the effective boolean value true; otherwise the quantified expression is false. This rule implies that, if the in-clauses generate zero binding tuples, the value of the quantified expression is true.

The scope of a variable bound in a quantified expression comprises all subexpressions of the quantified expression that appear after the variable binding. The scope does not include the expression to which the variable is bound.

Each variable bound in an in-clause of a quantified expression may have an optional type declaration, which is a datatype declared using the syntax in 2.4.4 SequenceType Matching. If the type of a value bound to the variable does not match the declared type according to the rules for SequenceType matching, a type error is raised.[err:XP0004][err:XP0006]

The order in which test expressions are evaluated for the various binding tuples is implementation-dependent. If the quantifier is some, an implementation may return true as soon as it finds one binding tuple for which the test expression has an effective boolean value of true, and it may raise a dynamic error as soon as it finds one binding tuple for which the test expression raises an error. Similarly, if the quantifier is every, an implementation may return false as soon as it finds one binding tuple for which the test expression has an effective boolean value of false, and it may raise a dynamic error as soon as it finds one binding tuple for which the test expression raises an error. As a result of these rules, the value of a quantified expression is not deterministic in the presence of errors, as illustrated in the examples below.

Here are some examples of quantified expressions:

  • This expression is true if every part element has a discounted attribute (regardless of the values of these attributes):

    every $part in //part satisfies $part/@discounted
    
  • This expression is true if at least one employee element satisfies the given comparison expression:

    some $emp in //employee satisfies ($emp/bonus > 0.25 * $emp/salary)
    
  • In the following examples, each quantified expression evaluates its test expression over nine tuples of variable bindings, formed from the Cartesian product of the sequences (1, 2, 3) and (2, 3, 4). The expression beginning with some evaluates to true, and the expression beginning with every evaluates to false.

    some $x in (1, 2, 3), $y in (2, 3, 4) 
         satisfies $x + $y = 4
    
    every $x in (1, 2, 3), $y in (2, 3, 4) 
         satisfies $x + $y = 4
    
  • This quantified expression may either return true or raise a type error, since its test expression returns true for one variable binding and raises a type error for another:

    some $x in (1, 2, "cat") satisfies $x * 2 = 4
    
  • This quantified expression may either return false or raise a type error, since its test expression returns false for one variable binding and raises a type error for another:

    every $x in (1, 2, "cat") satisfies $x * 2 = 4
    
  • This quantified expression contains a type declaration that is not satisfied by every item in the test expression. If the Static Typing Feature is implemented, this expression raises a type error during the analysis phase. Otherwise, the expression may either return true or raise a type error during the evaluation phase.

    some $x as xs:integer in (1, 2, "cat") satisfies $x * 2 = 4
    

3.12 Expressions on SequenceTypes

In addition to their use in function parameters and results, SequenceTypes are used in instance of, typeswitch, cast, castable, and treat expressions.

3.12.1 Instance Of

[49]    InstanceofExpr    ::=    TreatExpr ( "instance" "of" SequenceType )?

The boolean operator instance of returns true if the value of its first operand matches the SequenceType in its second operand, according to the rules for SequenceType matching; otherwise it returns false. For example:

  • 5 instance of xs:integer

    This example returns true because the given value is an instance of the given type.

  • 5 instance of xs:decimal

    This example returns true because the given value is an integer literal, and xs:integer is derived by restriction from xs:decimal.

  • <a>{5}</a> instance of xs:integer

    This example returns false because the given value is not an integer; instead, it is an element containing an integer.

  • . instance of element()

    This example returns true if the context item is an element node. If the context item is undefined, a dynamic error is raised.[err:XP0002]

3.12.2 Typeswitch

[38]    TypeswitchExpr    ::=    "typeswitch" "(" Expr ")" CaseClause+ "default" ("$" VarName)? "return" ExprSingle
[39]    CaseClause    ::=    "case" ("$" VarName "as")? SequenceType "return" ExprSingle

The typeswitch expression chooses one of several expressions to evaluate based on the dynamic type of an input value.

In a typeswitch expression, the typeswitch keyword is followed by an expression enclosed in parentheses, called the operand expression. This is the expression whose type is being tested. The remainder of the typeswitch expression consists of one or more case clauses and a default clause.

Each case clause specifies a SequenceType followed by a return expression. The effective case is the first case clause such that the value of the operand expression matches the SequenceType in the case clause, using the rules of SequenceType matching. The value of the typeswitch expression is the value of the return expression in the effective case. If the value of the operand expression is not a value of any type named in a case clause, the value of the typeswitch expression is the value of the return expression in the default clause.

A case or default clause may optionally specify a variable name. Within the return expression of the case or default clause, this variable name is bound to the value of the operand expression, and its static type is considered to be the SequenceType named in the case or default clause. If the return expression does not depend on the value of the operand expression, the variable may be omitted from the case or default clause.

The scope of a variable binding in a case or default clause comprises that clause. It is not an error for more than one case or default clause in the same typeswitch expression to bind variables with the same name.

The following example shows how a typeswitch expression might be used to process an expression in a way that depends on its dynamic type.

typeswitch($customer/billing-address)
   case $a as element(*, USAddress) return $a/state
   case $a as element(*, CanadaAddress) return $a/province
   case $a as element(*, JapanAddress) return $a/prefecture
   default return "unknown"

3.12.3 Cast

[52]    CastExpr    ::=    UnaryExpr ( "cast" "as" SingleType )?
[108]    SingleType    ::=    AtomicType "?"?

Occasionally it is necessary to convert a value to a specific datatype. For this purpose, XQuery provides a cast expression that creates a new value of a specific type based on an existing value. A cast expression takes two operands: an input expression and a target type. The type of the input expression is called the input type. The target type must be a named atomic type, represented by a QName, optionally followed by the occurrence indicator ? if an empty sequence is permitted. If the target type has no namespace prefix, it is considered to be in the default element/type namespace. The semantics of the cast expression are as follows:

  1. Atomization is performed on the input expression.

  2. If the result of atomization is a sequence of more than one atomic value, a type error is raised.[err:XP0004][err:XP0006]

  3. If the result of atomization is an empty sequence:

    1. If ? is specified after the target type, the result of the cast expression is an empty sequence.

    2. If ? is not specified after the target type, a type error is raised.[err:XP0004][err:XP0006]

  4. If the result of atomization is a single atomic value, the result of the cast expression depends on the input type and the target type. In general, the cast expression attempts to create a new value of the target type based on the input value. Only certain combinations of input type and target type are supported. A summary of the rules are listed below— the normative definition of these rules is given in [XQuery 1.0 and XPath 2.0 Functions and Operators]. For the purpose of these rules, an implementation may determine that one type is derived by restriction from another type either by examining the in-scope schema definitions or by using an alternative, implementation-dependent mechanism such as a data dictionary.

    1. cast is supported for the combinations of input type and target type listed in [XQuery 1.0 and XPath 2.0 Functions and Operators]. For each of these combinations, both the input type and the target type are primitive schema types. For example, a value of type xs:string can be cast into the type xs:decimal. For each of these built-in combinations, the semantics of casting are specified in [XQuery 1.0 and XPath 2.0 Functions and Operators].

    2. cast is supported if the input type is a non-primitive atomic type that is derived by restriction from the target type. In this case, the input value is mapped into the value space of the target type, unchanged except for its type. For example, if shoesize is derived by restriction from xs:integer, a value of type shoesize can be cast into the type xs:integer.

    3. cast is supported if the target type is a non-primitive atomic type and the input type is xs:string or xdt:untypedAtomic. The input value is first converted to a value in the lexical space of the target type by applying the whitespace normalization rules for the target type; a dynamic error [err:XP0029] is raised if the resulting lexical value does not satisfy the pattern facet of the target type. The lexical value is then converted to the value space of the target type using the schema-defined rules for the target type; a dynamic error[err:XP0029] is raised if the resulting value does not satisfy all the facets of the target type.

    4. cast is supported if the target type is a non-primitive atomic type that is derived by restriction from the input type. The input value must satisfy all the facets of the target type (in the case of the pattern facet, this is checked by generating a string representation of the input value, using the rules for casting to xs:string). The resulting value is the same as the input value, but with a different dynamic type.

    5. If a primitive type P1 can be cast into a primitive type P2, then any type derived by restriction from P1 can be cast into any type derived by restriction from P2, provided that the facets of the target type are satisfied. First the input value is cast to P1 using rule (b) above. Next, the value of type P1 is cast to the type P2, using rule (a) above. Finally, the value of type P2 is cast to the target type, using rule (d) above.

    6. For any combination of input type and target type that is not in the above list, a cast expression raises a type error.[err:XP0004][err:XP0006]

If casting from the input type to the target type is supported but nevertheless it is not possible to cast the input value into the value space of the target type, a dynamic error is raised.[err:XP0021] This includes the case when any facet of the target type is not satisfied. For example, the expression "2003-02-31" cast as xs:date would raise a dynamic error.

3.12.4 Castable

[51]    CastableExpr    ::=    CastExpr ( "castable" "as" SingleType )?

XQuery provides an expression that tests whether a given value is castable into a given target type. The expression V castable as T returns true if the value V can be successfully cast into the target type T by using a cast expression; otherwise it returns false. The castable predicate can be used to avoid errors at evaluation time. It can also be used to select an appropriate type for processing of a given value, as illustrated in the following example:

if ($x castable as hatsize) 
   then $x cast as hatsize 
   else if ($x castable as IQ) 
   then $x cast as IQ 
   else $x cast as xs:string

3.12.5 Constructor Functions

For every atomic type in the in-scope type definitions that is in a namespace, a constructor function is provided. In each case, the name of the constructor function is the same as the name of its target type (including namespace). The signature of the constructor function for type T is as follows:

T($arg as xdt:anyAtomicType?) as T?

Constructor functions are normatively defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In general, if the argument to a constructor function is of type xs:string, the string is whitespace-normalized and converted to the target type by schema validation; otherwise, the semantics of the constructor function are identical to $arg cast as T.

The following examples illustrate the use of constructor functions:

  • This example is equivalent to "2000-01-01" cast as xs:date.

    xs:date("2000-01-01")
    
  • This example is equivalent to ($floatvalue * 0.2E-5) cast as xs:decimal.

    xs:decimal($floatvalue * 0.2E-5)
    
  • This example returns a xdt:dayTimeDuration value equal to 21 days. It is equivalent to "P21D" cast as xdt:dayTimeDuration.

    xdt:dayTimeDuration("P21D")
    
  • If usa:zipcode is a user-defined atomic type in the in-scope type definitions, then the following expression is equivalent to the expression "12345" cast as usa:zipcode.

    usa:zipcode("12345")
    

Atomic types that are not in a namespace do not have constructor functions. To construct an instance of such a type, it is necessary to use a cast expression. For example, if the user-defined type apple is derived from xs:integer but is not in a namespace, an instance of this type can be constructed as follows (but only if the default element/type namespace is no namespace):

17 cast as apple

3.12.6 Treat

[50]    TreatExpr    ::=    CastableExpr ( "treat" "as" SequenceType )?

XQuery provides an expression called treat that can be used to modify the static type of its operand.

Like cast, the treat expression takes two operands: an expression and a SequenceType. Unlike cast, however, treat does not change the dynamic type or value of its operand. Instead, the purpose of treat is to ensure that an expression has an expected type at evaluation time.

The semantics of expr1 treat as type1 are as follows:

  • During static analysis:

    The static type of the treat expression is type1. This enables the expression to be used as an argument of a function that requires a parameter of type1.

  • During expression evaluation:

    If expr1 matches type1, using the rules for SequenceType matching, the treat expression returns the value of expr1; otherwise, it raises a dynamic error.[err:XP0050] If the value of expr1 is returned, its identity is preserved. The treat expression ensures that the value of its expression operand conforms to the expected type at run-time.

  • Example:

    $myaddress treat as element(*, USAddress)
    

    The static type of $myaddress may be element(*, Address), a less specific type than element(*, USAddress). However, at run-time, the value of $myaddress must match the type element(*, USAddress) using rules for SequenceType matching; otherwise a dynamic error is raised.[err:XP0050]

3.13 Validate Expressions

[58]    ValidateExpr    ::=    "validate" ValidationMode? "{" Expr "}"
[137]    ValidationMode    ::=    "lax" | "strict"

A validate expression can be used to validate a document node or an element node with respect to the in-scope schema definitions, using the schema validation process defined in [XML Schema]. If the operand of a validate expression does not evaluate to exactly one document or element node, a type error is raised.[err:XQ0030]

A validate expression returns a new node with its own identity and with no parent. The new node and its descendants are given type annotations and default values that are generated by applying a validation process to the operand node.

The validate expression begins by making a new copy of the operand node, including all its properties (base-uri, in-scope namespaces, etc.), and including new copies of all its attributes and descendant nodes (if any). In the following description, the copy of the operand node is called the candidate node, and the term contained nodes means the element and attribute nodes that have the candidate node as an ancestor. The candidate node is processed according to the following rules, and is then returned as the result of the validate expression.

3.13.1 Validating an Element Node

If the candidate node is an element node, the result of the validate expression is defined by the following rules.

  • If ValidationMode is strict or is not specified, schema validity assessment is performed on the candidate node as follows:

    1. The candidate node is serialized to textual XML form, according to the process defined in 2.2.4 Serialization using the XML output method, with all parameters defaulted. Note that this process discards any existing type annotations.

    2. The resulting XML document is parsed to create an XML Information Set (see [XML Infoset]).

    3. The resulting Information Set is validated as follows:

      1. Validity assessment is carried out on the root element information item, according to the rules in [XML Schema] Part 1, Section 3.3.4, "Schema-Validity Assessment (Element)", using the in-scope schema definitions as the effective schema. The process of validation applies recursively to contained elements and attributes to the extent required by the effective schema. Note that the validity assessment process is affected by the presence or absence of an xsi:type attribute on the candidate node, and may generate new information items such as default attributes.

      2. During validity assessment, the following special rules are in effect:

        • The validation rule "Validation Root Valid (ID/IDREF)" is not applied. This means that validation will not fail if there are non-unique ID values or dangling IDREF values in the subtree being validated.

        • The validation rule "Validation Rule: Identity-constraint Satisfied" is not applied.

        • There is no check that the document contains unparsed entities whose names match the values of nodes of type xs:ENTITY or xs:ENTITIES.

        • There is no check that the document contains notations whose names match the values of nodes of type xs:NOTATION.

    4. If the result of schema validity assessment is a PSVI in which the root element information item has the validity property valid, this PSVI is converted back into the Data Model by the process described in [XQuery 1.0 and XPath 2.0 Data Model] Section 3.3, "Construction from a PSVI", replacing the candidate node. Otherwise, a dynamic error is raised. [err:XQ0027] In effect this means that the candidate node must have a top-level element declaration in the effective schema, and must conform to this declaration.

  • If ValidationMode is lax, the candidate node is processed as though ValidationMode were strict, with the following exception: Whereas strict validation fails if the outcome of validity assessment is a validity property of invalid or notKnown, lax validation fails only if the outcome of validity assessment is a validity property of invalid. That is, lax validation does not raise a type error when the outcome is notKnown.

    In practice this means that the candidate node must conform to its top-level declaration if such a declaration exists in the effective schema. If no such declaration exists, then the candidate node is not validated, but its attributes and children are validated, again with lax validation. After validation, elements whose validity property is notKnown are represented in the Data Model as element nodes with type xs:anyType. Attributes whose validity property is notKnown are represented in the Data Model as attribute nodes with type xdt:untypedAtomic.

3.13.2 Validating a Document Node

If the candidate node of a validate expression is a document node, the result of the validate expression is defined by the following rules.

  1. A dynamic error [err:XQ0061] is raised if the children of the candidate node do not consist of exactly one element node and zero or more comment and processing instruction nodes, in any order.

  2. The single element node child is serialized and validated, as described in 3.13.1 Validating an Element Node, with the following special rules:

    1. The validation rule "Validation Root Valid (ID/IDREF)" is applied. A dynamic error [err:XQ0062] is raised if non-unique ID values or dangling IDREF values are found in the document tree.

    2. Identity constraints, as defined in section 3.11 of [XML Schema] Part 1, are checked. (This refers to constraints defined using xs:unique, xs:key, and xs:keyref.) A dynamic error [err:XQ0062] is raised if an identity constraint is found to be violated.

  3. The next step depends on the validity property of the root information item in the PSVI that results from the validation process. If this property is valid, the PSVI is converted back into the Data Model as described in [XQuery 1.0 and XPath 2.0 Data Model] Section 3.3, "Construction from a PSVI". The resulting node hierarchy replaces the original element child of the candidate node, taking its place among other descendants of the candidate node, which remain unchanged. Otherwise, a dynamic error is raised. [err:XQ0027]

4 Modules and Prologs

[1]    Module    ::=    VersionDecl? (MainModule | LibraryModule)
[3]    MainModule    ::=    Prolog QueryBody
[4]    LibraryModule    ::=    ModuleDecl Prolog
[6]    Prolog    ::=    (Setter Separator)* ((Import | NamespaceDecl | VarDecl | FunctionDecl) Separator)*
[7]    Setter    ::=    XMLSpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | DefaultNamespaceDecl | DefaultOrderingDecl
[8]    Import    ::=    SchemaImport | ModuleImport
[9]    Separator    ::=    ";"
[25]    QueryBody    ::=    Expr

[Definition: A query can be assembled from one or more fragments called modules. Each module is either a main module or a library module.] Each module, in turn, consists of one or more parts called module resources. [Definition: Each module resource is a fragment of XQuery code that conforms to the Module grammar and can independently undergo the static analysis phase described in 2.2.3 Expression Processing.]

[Definition: A main module consists of single module resource containing a Prolog followed by a Query Body.] A query has exactly one main module. In a main module, the Query Body can be evaluated, and its value is the result of the query.

[Definition: A module that does not contain a Query Body is called a library module.] A library module may consist of multiple module resources, each containing a module declaration followed by a Prolog. Multiple module resources are identified as being parts of the same library module if they name the same target namespace in their module declarations. A library module cannot be evaluated directly; instead, it provides function and variable declarations that can be imported into other modules.

No module resource may contain both a module declaration and a Query Body.

[Definition: A Prolog is a series of declarations and imports that define the processing environment for the module resource that contains the Prolog.] Each declaration or import is followed by a semicolon. [Definition: Certain declarations in a Prolog are called setters because they set the value of some property that influences query processing, such as construction mode, ordering mode, or default collation.] These setters, if present, must occur at the beginning of the Prolog, in any order. A Prolog may also include imports of schemas and modules, and declarations of namespace prefixes, variables, and functions. [Definition: Each imported schema or module is identified by its target namespace, which is the namespace of the objects (such as elements or functions) that are defined by the schema or module.]

[Definition: The Query Body, if present, consists of an expression that defines the result of the query.] Evaluation of expressions is described in 3 Expressions. A module can be evaluated only if it has a Query Body.

4.1 Version Declaration

[2]    VersionDecl    ::=    "xquery" "version" StringLiteral Separator

[Definition: Any module resource may contain a version declaration. If present, the version declaration occurs at the beginning of the module resource and identifies the applicable XQuery syntax and semantics for the module resource.] The version number "1.0" indicates the requirement that the module resource must be processed by an XQuery Version 1.0 processor. If the version declaration is not present, the version is presumed to be "1.0". An XQuery implementation must raise a static error [err:XQ0031] when processing a module resource labeled with a version that the implementation does not support. It is the intent of the XQuery working group to give later versions of this specification numbers other than "1.0", but this intent does not indicate a commitment to produce any future versions of XQuery, nor if any are produced, to use any particular numbering scheme.

The following is an example of a version declaration:

xquery version "1.0";

4.2 Module Declaration

[5]    ModuleDecl    ::=    "module" "namespace" NCName "=" StringLiteral Separator

[Definition: A module declaration serves to identify a module resource as part of a library module. A module declaration consists of the keyword module followed by a namespace prefix and a string literal which must contain a valid URI. [err:XQ0046]] The URI identifies the target namespace of the library module, which is the namespace for all variables and functions exported by the library module. The name of every variable and function declared in a library module must have a namespace URI that is the same as the target namespace of the module.[err:XQ0048]

Any module resource may import a library module by means of a module import that specifies the target namespace of the library module to be imported. When a module imports one or more library modules, the variables and functions declared in the imported modules are added to the static context and (where applicable) to the dynamic context of the importing module.

The following is an example of a module declaration:

module namespace math = "http://example.org/math-functions";

4.3 Xmlspace Declaration

[11]    XMLSpaceDecl    ::=    "declare" "xmlspace" ("preserve" | "strip")

[Definition: The xmlspace declaration in a Prolog controls whether boundary whitespace is preserved by direct element constructors during execution of the query.] If xmlspace preserve is specified, boundary whitespace is preserved. If xmlspace strip is specified or if no xmlspace declaration is present, boundary whitespace is stripped (deleted). A further discussion of whitespace in constructed elements can be found in 3.7.1.4 Whitespace in Element Content.

The following example illustrates an xmlspace declaration:

declare xmlspace preserve;

4.4 Default Collation Declaration

[14]    DefaultCollationDecl    ::=    "declare" "default" "collation" StringLiteral

A Prolog may declare a default collation, which is the name of the collation to be used by functions and operators that require a collation if no other collation is specified. For example, the gt operator on strings is defined by a call to the fn:compare function, which takes an optional collation parameter. Since the gt operator does not specify a collation, the fn:compare function implements gt by using the default collation specified in the Prolog. The default collation is identified by a literal string which must contain a valid URI. [err:XQ0046]

If a Prolog specifies no default collation, the Unicode codepoint collation (http://www.w3.org/2004/07/xpath-functions/collation/codepoint) is used unless the implementation provides a different default collation.

The following example illustrates a default collation declaration:

declare default collation
         "http://example.org/languages/Icelandic";

If a Prolog specifies more than one default collation, or the value specified does not identify a collation known to the implementation, a static error is raised.[err:XQ0038]

4.5 Base URI Declaration

[15]    BaseURIDecl    ::=    "declare" "base-uri" StringLiteral

A base URI declaration specifies the base URI property of the static context, which is used when resolving relative URIs within a module resource. A static error [err:XQ0032] is raised if more than one base URI declaration is found in a Prolog. A static error [err:XQ0046] is raised if the string literal in a base URI declaration does not contain a valid URI. Note that the fn:doc function resolves a relative URI using the base URI of the calling module.

The following is an example of a base URI declaration:

declare base-uri "http://example.org";

4.6 Construction Declaration

[20]    ConstructionDecl    ::=    "declare" "construction" ("preserve" | "strip")

A construction declaration in a Prolog sets the construction mode in the static context to preserve or strip. The construction mode governs the behavior of element constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and the attributes and descendants of the constructed element retain their original types. If construction mode is strip, the type of the constructed element node and all its descendants is xdt:untyped, and attributes of the constructed element have type xdt:untypedAtomic. Element constructors are described in 3.7.1 Direct Element Constructors and 3.7.3.1 Computed Element Constructors.

The following example illustrates a construction declaration:

declare construction strip;

If a Prolog specifies more than one construction declaration, a static error is raised.[err:XQ0067]

4.7 Default Namespace Declaration

[12]    DefaultNamespaceDecl    ::=    (("declare" "default" "element") | ("declare" "default" "function")) "namespace" StringLiteral

Default namespace declarations can be used in a Prolog to facilitate the use of unprefixed QNames. The string literal used in a default namespace declaration must be a valid URI or a zero-length string. [err:XQ0046] The following kinds of default namespace declarations are supported:

  • A default element/type namespace declaration declares a namespace URI that is associated with unprefixed names of elements and types. This declaration is recorded as the default element/type namespace in the static context. A Prolog may contain at most one default element/type namespace declaration.[err:XQ0066] If the StringLiteral in a default element/type namespace declaration is a zero-length string, the default element/type namespace is set to "none," and unprefixed names of elements and types are considered to be in no namespace. The following example illustrates the declaration of a default namespace for elements and types:

    declare default element namespace "http://example.org/names";
    

    A default element/type namespace declaration may be overridden by a namespace declaration attribute in a direct element constructor or by a local namespace declaration in a computed element constructor.

  • A default function namespace declaration declares a namespace URI that is associated with unprefixed names of functions in function calls. This declaration is recorded as the default function namespace in the static context. A Prolog may contain at most one default function namespace declaration.[err:XQ0066] If the StringLiteral in a default function namespace declaration is a zero-length string, a static error is raised. [err:XQ0063] If no default function namespace is declared, the default function namespace is the namespace of XPath/XQuery functions, http://www.w3.org/2004/07/xpath-functions (however, this default may be overridden by an implementation.) The following example illustrates the declaration of a default function namespace:

    declare default function namespace 
         "http://example.org/math-functions";
    

    The effect of declaring a default function namespace is that all functions in the default function namespace, including implicitly-declared constructor functions, are aliased with a name that has the original local name, but no namespace URI. The function may then be called using either its original name or its alias—that is, the namespace prefix becomes optional. When a function call uses a function name with no prefix, the local name of the function must match a function (including implicitly-declared constructor functions) in the default function namespace.[err:XP0017]

Unprefixed attribute names and variable names are in no namespace.

4.8 Default Ordering Declaration

[13]    DefaultOrderingDecl    ::=    "declare" "ordering" ("ordered" | "unordered")

[Definition: A default ordering declaration sets the ordering mode in the static context.] This ordering mode applies to all expressions in a module resource (including both the Prolog and the Query Body, if any), unless overridden by an ordered or unordered expression. A static error [err:XQ0065] is raised if more than one default ordering declaration is found in a Prolog.

Ordering mode affects the behavior of path expressions, union, intersect, and except expressions, and FLWOR expressions that have no order by clause. If ordering mode is ordered, node sequences returned by path, union, intersect, and except expressions are in document order; otherwise the order of these return sequences is implementation-dependent. The effect of ordering mode on FLWOR expressions is described in 3.8 FLWOR Expressions.

The following example illustrates a default ordering declaration:

declare ordering unordered;

4.9 Schema Import

[16]    SchemaImport    ::=    "import" "schema" SchemaPrefix? StringLiteral (("at" StringLiteral) ("," StringLiteral)*)?
[17]    SchemaPrefix    ::=    ("namespace" NCName "=") | ("default" "element" "namespace")

[Definition: A schema import imports the element, attribute, and type definitions from a schema into the in-scope schema definitions.] The schema to be imported is identified by its target namespace. The schema import may bind a namespace prefix to the target namespace of the imported schema, or may declare that target namespace to be the default element/type namespace. The schema import may also provide optional hints for locating the schema.

The string literals in a schema import must be valid URIs. [err:XQ0046] The first of these string literals specifies the target namespace of the schema to be imported. The string literals that follow the at keyword are optional location hints, and can be interpreted or disregarded in an implementation-dependent way. Multiple location hints might be used to indicate more than one possible place to look for the schema or multiple physical resources to be assembled to form the schema.

A schema import that specifies a zero-length string as target namespace is considered to import a schema that has no target namespace. Such a schema import may not bind a namespace prefix [err:XQ0057], but it may set the default element/type namespace to "no namespace", enabling the definitions in the imported namespace to be referenced. If the default element/type namespace is not set to "no namespace", there is no way to reference the definitions in an imported schema that has no target namespace.

It is a static error [err:XQ0058] if more than one schema import in the same Prolog specifies the same target namespace. It is a static error [err:XQ0059] if the implementation is not able to process a schema import by finding a valid schema with the specified target namespace. It is a static error [err:XQ0035] if multiple imported schemas, or multiple physical resorces within one schema, contain definitions for the same name in the same symbol space (for example, two definitions for the same element name, even if the definitions are consistent). However, it is not an error to import the schema with target namespace http://www.w3.org/2001/XMLSchema (predeclared prefix xs), even though the built-in types defined in this schema are implicitly included in the in-scope type definitions.

The following example imports the schema for an XHTML document, specifying both its target namespace and its location, and binding the prefix xhtml to this namespace:

import schema namespace xhtml="http://www.w3.org/1999/xhtml" 
   at "http://example.org/xhtml/xhtml.xsd";

The following example imports a schema by specifying only its target namespace, and makes it the default element/type namespace:

import schema default element namespace "http://example.org/abc";

The following example imports a schema that has no target namespace, providing a location hint, and sets the default element/type namespace to "no namespace" so that the definitions in the imported schema can be referenced:

import schema default element namespace "" 
at "http://example.org/xyz.xsd";

The following example imports a schema that has no target namespace and sets the default element/type namespace to "no namespace". Since no location hint is provided, it is up to the implementation to find the schema to be imported.

import schema default element namespace "";

4.10 Module Import

[18]    ModuleImport    ::=    "import" "module" ("namespace" NCName "=")? StringLiteral (("at" StringLiteral) ("," StringLiteral)*)?

[Definition: A module import imports the function declarations and variable declarations from a library module into the function signatures and in-scope variables of the importing module resource.] The module to be imported is identified by its target namespace. The module import may bind a namespace prefix to the target namespace of the imported module, and it may provide optional hints for locating the module resources of the imported module.

The string literals in a module import must be valid URIs. [err:XQ0046] The first of these string literals specifies the target namespace of the module to be imported. The string literals that follow the at keyword are optional location hints, and can be interpreted or disregarded in an implementation-defined way. If the imported module consists of multiple module resources, all the function and variable declarations in those module resources are imported.

It is a static error [err:XQ0047] if more than one module import in a Prolog specifies the same target namespace. It is a static error [err:XQ0056] if the target namespace of the module to be imported is the same as the target namespace of the importing module. It is a static error [err:XQ0059] if the implementation is not able to process a module import by finding a valid module definition with the specified target namespace. It is a static error if multiple imported modules, or multiple module resources within an imported module, contain definitions for the same name in the same symbol space (for example, two definitions for the same function, even if the definitions are consistent).[err:XQ0034][err:XQ0049]

Each module resource has its own static context. A module import imports only functions and variable declarations; it does not import other objects from the imported module, such as its in-scope schema definitions or statically known namespaces. Module imports are not transitive—that is, importing a module provides access only to function and variable declarations contained directly in the imported module. For example, if module A imports module B, and module B imports module C, module A does not have access to the functions and variables declared in module C. Two modules may import each other.

It is a type error [err:XQ0036] to import a module if the importing module's in-scope type definitions do not include definitions for the type names that appear in variable declarations, function parameters, or function returns found in the imported module. It is a static error [err:XQ0037] to import a module that contains function declarations or variable declarations whose names are already declared in the static context of the importing module.

To illustrate the above rules, suppose that a certain schema defines a type named triangle. Suppose that a library module imports the schema, binds its target namespace to the prefix geometry, and declares a function with the following function signature: math:area($t as geoetry:triangle) as xs:double. If a query wishes to use this function, it must import both the library module and the schema on which it is based. Importing the library module alone would not provide access to the definition of the type geometry:triangle used in the signature of the area function.

The following example illustrates a module import:

import module namespace math = "http://example.org/math-functions";

4.11 Namespace Declaration

[10]    NamespaceDecl    ::=    "declare" "namespace" NCName "=" StringLiteral

[Definition: A namespace declaration declares a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of statically known namespaces.] The string literal used in a namespace declaration must be a valid URI [err:XQ0046] or a zero-length string. The namespace declaration is in scope throughout the query in which it is declared, unless it is overridden by a namespace declaration attribute in a direct element constructor or by a local namespace declaration in a computed element constructor.

The following query illustrates a namespace declaration:

declare namespace foo = "http://example.org";
<foo:bar> Lentils </foo:bar>

In the query result, the newly created node is in the namespace associated with the namespace URI http://example.org.

Multiple declarations of the same namespace prefix in a Prolog result in a static error.[err:XQ0033] However, a declaration of a namespace in a Prolog can override a prefix that has been predeclared in the static context.

It is a static error [err:XP0008] to use a QName with a namespace prefix that has not been declared.

XQuery has several predeclared namespace prefixes that are present in the statically known namespaces before each query is processed. These prefixes may be used without an explicit declaration. They may be overridden by namespace declarations in a Prolog or by namespace declaration attributes or local namespace declarations on constructed elements (except for the prefix xml, which may not be redeclared.) The predeclared namespace prefixes are as follows:

  • xml = http://www.w3.org/XML/1998/namespace

  • xs = http://www.w3.org/2001/XMLSchema

  • xsi = http://www.w3.org/2001/XMLSchema-instance

  • fn = http://www.w3.org/2004/07/xpath-functions

  • xdt = http://www.w3.org/2004/07/xpath-datatypes

  • local = http://www.w3.org/2004/07/xquery-local-functions (see 4.13 Function Declaration.)

Additional predeclared namespace prefixes may be added to the statically known namespaces by an implementation.

The namespace prefix xmlns also has a special significance (it identifies a namespace declaration attribute), and it may not be redeclared.

If the StringLiteral part of a namespace declaration is a zero-length string, the following rules apply:

  • If the implementation supports [XML Names 1.1], any existing namespace binding for the given prefix is removed from the statically known namespaces. This feature provides a way to remove predeclared namespace prefixes such as local.

  • If the implementation does not support [XML Names 1.1], a static error is raised. [err:XQ0053]

  • It is implementation-defined whether a given implementation supports [XML Names 1.1].

When element or attribute names are compared, they are considered identical if the local parts and namespace URIs match on a codepoint basis. Namespace prefixes need not be identical for two names to match, as illustrated by the following example:

declare namespace xx = "http://example.org";

let $i := <foo:bar xmlns:foo = "http://example.org">
              <foo:bing> Lentils </foo:bing>
          </foo:bar>
return $i/xx:bing

Although the namespace prefixes xx and foo differ, both are bound to the namespace URI "http://example.org". Since xx:bing and foo:bing have the same local name and the same namespace URI, they match. The output of the above query is as follows.

<foo:bing> Lentils </foo:bing>

4.12 Variable Declaration

[19]    VarDecl    ::=    "declare" "variable" "$" VarName TypeDeclaration? ((":=" ExprSingle) | "external")
[136]    VarName    ::=    QName
[109]    TypeDeclaration    ::=    "as" SequenceType

A variable declaration adds the static type of a variable to the in-scope variables, and may also add a value for the variable to the variable values. If the expanded QName of the variable is the same as that of another variable in in-scope variables, a static error is raised.[err:XQ0049]

If a variable declaration includes a type, that type is added to the static context as the type of the variable. If a variable declaration includes an expression but not an explicit type, the static type of the variable is inferred from the static type of the expression. If a variable declaration includes both a type and an expression, the static type of the expression must be compatible with the declared static type; otherwise a type error is raised.[err:XP0004]

[Definition: If a variable declaration includes an expression, the expression is called an initializing expression.] The initializing expression for a given variable must be evaluated before the evaluation of any expression that references the variable. The static context for an initializing expression includes all functions that are declared or imported anywhere in the Prolog, but it includes only those variables and namespaces that are declared or imported earlier in the Prolog than the variable that is being initialized. If an initializing expression cannot be evaluated because of a circularity (for example, it depends on a function that in turn depends on the value of the variable that is being initialized), a static error is raised.[err:XQ0054]

If the variable declaration includes the keyword external, a value must be provided for the variable by the external environment before the query can be evaluated. If an external variable declaration also includes a declared type, the value provided by the external environment must match the declared type, using the matching rules in 2.4.4 SequenceType Matching (see 2.2.5 Consistency Constraints). If an external variable declaration does not include a declared type, the type and a matching value must be provided by the external environment at evaluation time. The static type of such a variable is considered to be item()*.

All variable names declared in a library module must (when expanded) be in the target namespace of the library module.[err:XQ0048] When a library module is imported, variables declared in the imported module are added to the in-scope variables of the importing module.

Variable names that have no namespace prefix are in no namespace. Variable declarations that have no namespace prefix may appear only in a main module.

The term variable declaration always refers to a declaration of a variable in a Prolog. The binding of a variable to a value in a query expression, such as a FLWOR expression, is known as a variable binding, and does not make the variable visible to an importing module.

Here are some examples of variable declarations:

  • The following declaration specifies both the type and the value of a variable. This declaration causes the type xs:integer to be associated with variable $x in the static context, and the value 7 to be associated with variable $x in the dynamic context.

    declare variable $x as xs:integer := 7;
    
  • The following declaration specifies a value but not a type. The static type of the variable is inferred from the static type of its value. In this case, the variable $x has a static type of xs:decimal, inferred from its value which is 7.5.

    declare variable $x := 7.5;
    
  • The following declaration specifies a type but not a value. The keyword external indicates that the value of the variable will be provided by the external environment. At evaluation time, if the variable $x in the dynamic context does not have a value of type xs:integer, a type error is raised.

    declare variable $x as xs:integer external;
    
  • The following declaration specifies neither a type nor a value. It simply declares that the query depends on the existence of a variable named $x, whose type and value will be provided by the external environment. During query analysis, the type of $x is considered to be item()*. During query evaluation, the dynamic context must include a type and a value for $x, and its value must be compatible with its type.

    declare variable $x external;
    

4.13 Function Declaration

In addition to the built-in functions described in [XQuery 1.0 and XPath 2.0 Functions and Operators], XQuery allows users to declare functions of their own. A function declaration specifies the name of the function, the names and datatypes of the parameters, and the datatype of the result. All datatypes are specified using the syntax described in 2.4 Types. A function declaration causes the declared function to be added to the function signatures of the module resource in which it appears.

[21]    FunctionDecl    ::=    "declare" "function" QName "(" ParamList? (")" | (")" "as" SequenceType)) (EnclosedExpr | "external")
[22]    ParamList    ::=    Param ("," Param)*
[23]    Param    ::=    "$" VarName TypeDeclaration?
[109]    TypeDeclaration    ::=    "as" SequenceType

A function declaration specifies whether a function is user-defined or external. [Definition: For a user-defined function, the function declaration includes an expression called the function body that defines how the result of the function is computed from its parameters.]. The static context for a function body includes all functions that are declared or imported anywhere in the Prolog, but it includes only those variables and namespaces that are declared or imported earlier in the Prolog than the function that is being defined.

[Definition: External functions are functions that are implemented outside the query environment.] For example, an XQuery implementation might provide a set of external functions in addition to the core function library described in [XQuery 1.0 and XPath 2.0 Functions and Operators]. External functions are identified by the keyword external. The purpose of a function declaration for an external function is to declare the datatypes of the function parameters and result, for use in type checking of the query that contains or imports the function declaration.

An XQuery implementation may provide a facility whereby external functions can be implemented using a host programming language, but it is not required to do so. If such a facility is provided, the protocols by which parameters are passed to an external function, and the result of the function is returned to the invoking query, are implementation-defined. An XQuery implementation may augment the type system of [XQuery 1.0 and XPath 2.0 Data Model] with additional types that are designed to facilitate exchange of data with host programming languages, or it may provide mechanisms for the user to define such types. For example, a type might be provided that encapsulates an object returned by an external function, such as an SQL database connection. These additional types, if defined, are considered to be derived by restriction from xdt:anyAtomicType.

Every function must be in a namespace--that is, every declared function name must (when expanded) have a non-empty namespace URI. [err:XQ0060] Every function name declared in a library module must (when expanded) be in the target namespace of the library module.[err:XQ0048] It is a static error [err:XQ0045] if the function name in a function declaration (when expanded) is in any of the following namespaces:

  • http://www.w3.org/XML/1998/namespace

  • http://www.w3.org/2001/XMLSchema

  • http://www.w3.org/2001/XMLSchema-instance

  • http://www.w3.org/2004/07/xpath-functions

  • http://www.w3.org/2004/07/xpath-datatypes

If the expanded QName and number of arguments of the declared function are the same as the expanded QName and number of arguments of another function in function signatures, a static error is raised.[err:XQ0034]

In order to allow main modules to declare functions for local use within the module without defining a new namespace, XQuery predefines the namespace prefix local to the namespace http://www.w3.org/2004/07/xquery-local-functions, and reserves this namespace for use in defining local functions.

If a function parameter is declared using a name but no type, its default type is item*. If the result type is omitted from a function declaration, its default result type is item*.

The parameters of a function declaration are considered to be variables whose scope is the function body. It is an static error [err:XQ0039] for a function declaration to have more than one parameter with the same name. The type of a function parameter can be any type that can be expressed as a SequenceType (see 2.4 Types).

The following example illustrates the declaration and use of a local function that accepts a sequence of employee elements, summarizes them by department, and returns a sequence of dept elements.

  • Using a function, prepare a summary of employees that are located in Denver.

    declare function local:summary($emps as element(employee)*) 
       as element(dept)*
    {
       for $d in fn:distinct-values($emps/deptno)
       let $e := $emps[deptno = $d]
       return
          <dept>
             <deptno>{$d}</deptno>
             <headcount> {fn:count($e)} </headcount>
             <payroll> {fn:sum($e/salary)} </payroll>
          </dept>
    };
    
    local:summary(fn:doc("acme_corp.xml")//employee[location = "Denver"])
    

Rules for converting function arguments to their declared parameter types, and for converting the result of a function to its declared result type, are described in 3.1.5 Function Calls

A function declaration may be recursive—that is, it may reference itself. Mutually recursive functions, whose bodies reference each other, are also allowed. The following example declares a recursive function that computes the maximum depth of a node hierarchy, and calls the function to find the maximum depth of a particular document. In its declaration, the user-declared function local:depth calls the built-in functions empty and max, which are in the default function namespace.

  • Find the maximum depth of the document named partlist.xml.

    declare function local:depth($e as node()) as xs:integer
    {
       (: A node with no children has depth 1 :)
       (: Otherwise, add 1 to max depth of children :)
       if (fn:empty($e/*)) then 1
       else fn:max(for $c in $e/* return local:depth($c)) + 1
    };
    
    local:depth(fn:doc("partlist.xml"))
    

Since a constructor function is effectively declared for every user-defined atomic type in the in-scope type definitions, a static error [err:XQ0034] is raised if the Prolog attempts to declare a function with the same expanded QName as any of these types.

Note:

If a future version of XQuery supports overloading of user-declared functions, an ambiguity may arise between a function that takes a node as parameter and a function with the same name that takes an atomic value as parameter (since a function call automatically extracts the atomic value of a node when necessary). The designers of such a future version of XQuery can avoid this ambiguity by writing suitable rules to govern function overloading. Nevertheless, users who are concerned about this possibility may choose to explicitly extract atomic values from nodes when calling functions that expect atomic values.

A XQuery Grammar

A.1 EBNF

The following grammar uses the same simple Extended Backus-Naur Form (EBNF) notation as [XML 1.0] with the following minor differences. The notation "< ... >" is used to indicate a grouping of terminals that together may help disambiguate the individual symbols. To help readability, this "< ... >" notation is absent in the EBNF in the main body of this document. This appendix is the normative version of the EBNF.

Comments on grammar productions are between '/*' and '*/' symbols - please note that these comments are normative. A 'gn:' prefix means a 'Grammar Note', and is meant as a clarification for parsing rules, and is explained in A.1.1 Grammar Notes. A 'ws:' prefix explains the whitespace rules for the production, the details of which are explained in A.2.2 Whitespace Rules

[1]    Module    ::=    VersionDecl? (MainModule | LibraryModule)
[2]    VersionDecl    ::=    <"xquery" "version" StringLiteral> Separator
[3]    MainModule    ::=    Prolog QueryBody
[4]    LibraryModule    ::=    ModuleDecl Prolog
[5]    ModuleDecl    ::=    <"module" "namespace"> NCName "=" StringLiteral Separator
[6]    Prolog    ::=    (Setter Separator)* ((Import | NamespaceDecl | VarDecl | FunctionDecl) Separator)*
[7]    Setter    ::=    XMLSpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | DefaultNamespaceDecl | DefaultOrderingDecl
[8]    Import    ::=    SchemaImport | ModuleImport
[9]    Separator    ::=    ";"
[10]    NamespaceDecl    ::=    <"declare" "namespace"> NCName "=" StringLiteral
[11]    XMLSpaceDecl    ::=    <"declare" "xmlspace"> ("preserve" | "strip")
[12]    DefaultNamespaceDecl    ::=    (<"declare" "default" "element"> | <"declare" "default" "function">) "namespace" StringLiteral
[13]    DefaultOrderingDecl    ::=    <"declare" "ordering"> ("ordered" | "unordered")
[14]    DefaultCollationDecl    ::=    <"declare" "default" "collation"> StringLiteral
[15]    BaseURIDecl    ::=    <"declare" "base-uri"> StringLiteral
[16]    SchemaImport    ::=    <"import" "schema"> SchemaPrefix? StringLiteral (<"at" StringLiteral> ("," StringLiteral)*)?
[17]    SchemaPrefix    ::=    ("namespace" NCName "=") | (<"default" "element"> "namespace")
[18]    ModuleImport    ::=    <"import" "module"> ("namespace" NCName "=")? StringLiteral (<"at" StringLiteral> ("," StringLiteral)*)?
[19]    VarDecl    ::=    <"declare" "variable" "$"> VarName TypeDeclaration? ((":=" ExprSingle) | "external")
[20]    ConstructionDecl    ::=    <"declare" "construction"> ("preserve" | "strip")
[21]    FunctionDecl    ::=    <"declare" "function"> <QName "("> ParamList? (")" | (<")" "as"> SequenceType)) (EnclosedExpr | "external")
[22]    ParamList    ::=    Param ("," Param)*
[23]    Param    ::=    "$" VarName TypeDeclaration?
[24]    EnclosedExpr    ::=    "{" Expr "}"
[25]    QueryBody    ::=    Expr
[26]    Expr    ::=    ExprSingle ("," ExprSingle)*
[27]    ExprSingle    ::=    FLWORExpr
| QuantifiedExpr
| TypeswitchExpr
| IfExpr
| OrExpr
[28]    FLWORExpr    ::=    (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle
[29]    ForClause    ::=    <"for" "$"> VarName TypeDeclaration? PositionalVar? "in" ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle)*
[30]    PositionalVar    ::=    "at" "$" VarName
[31]    LetClause    ::=    <"let" "$"> VarName TypeDeclaration? ":=" ExprSingle ("," "$" VarName TypeDeclaration? ":=" ExprSingle)*
[32]    WhereClause    ::=    "where" Expr
[33]    OrderByClause    ::=    (<"order" "by"> | <"stable" "order" "by">) OrderSpecList
[34]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[35]    OrderSpec    ::=    ExprSingle OrderModifier
[36]    OrderModifier    ::=    ("ascending" | "descending")? (<"empty" "greatest"> | <"empty" "least">)? ("collation" StringLiteral)?
[37]    QuantifiedExpr    ::=    (<"some" "$"> | <"every" "$">) VarName TypeDeclaration? "in" ExprSingle ("," "$" VarName TypeDeclaration? "in" ExprSingle)* "satisfies" ExprSingle
[38]    TypeswitchExpr    ::=    <"typeswitch" "("> Expr ")" CaseClause+ "default" ("$" VarName)? "return" ExprSingle
[39]    CaseClause    ::=    "case" ("$" VarName "as")? SequenceType "return" ExprSingle
[40]    IfExpr    ::=    <"if" "("> Expr ")" "then" ExprSingle "else" ExprSingle
[41]    OrExpr    ::=    AndExpr ( "or" AndExpr )*
[42]    AndExpr    ::=    ComparisonExpr ( "and" ComparisonExpr )*
[43]    ComparisonExpr    ::=    RangeExpr ( (ValueComp
| GeneralComp
| NodeComp) RangeExpr )?
[44]    RangeExpr    ::=    AdditiveExpr ( "to" AdditiveExpr )?
[45]    AdditiveExpr    ::=    MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
[46]    MultiplicativeExpr    ::=    UnionExpr ( ("*" | "div" | "idiv" | "mod") UnionExpr )*
[47]    UnionExpr    ::=    IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
[48]    IntersectExceptExpr    ::=    InstanceofExpr ( ("intersect" | "except") InstanceofExpr )*
[49]    InstanceofExpr    ::=    TreatExpr ( <"instance" "of"> SequenceType )?
[50]    TreatExpr    ::=    CastableExpr ( <"treat" "as"> SequenceType )?
[51]    CastableExpr    ::=    CastExpr ( <"castable" "as"> SingleType )?
[52]    CastExpr    ::=    UnaryExpr ( <"cast" "as"> SingleType )?
[53]    UnaryExpr    ::=    ("-" | "+")* ValueExpr
[54]    ValueExpr    ::=    ValidateExpr | PathExpr
[55]    GeneralComp    ::=    "=" | "!=" | "<" | "<=" | ">" | ">=" /* gn: lt */
[56]    ValueComp    ::=    "eq" | "ne" | "lt" | "le" | "gt" | "ge"
[57]    NodeComp    ::=    "is" | "<<" | ">>"
[58]    ValidateExpr    ::=    (<"validate" "{"> | (<"validate" ValidationMode> "{")) Expr "}" /* gn: validate */
[59]    PathExpr    ::=    ("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
/* gn: leading-lone-slash */
[60]    RelativePathExpr    ::=    StepExpr (("/" | "//") StepExpr)*
[61]    StepExpr    ::=    AxisStep | FilterExpr
[62]    AxisStep    ::=    (ForwardStep | ReverseStep) PredicateList
[63]    ForwardStep    ::=    (ForwardAxis NodeTest) | AbbrevForwardStep
[64]    ForwardAxis    ::=    <"child" "::">
| <"descendant" "::">
| <"attribute" "::">
| <"self" "::">
| <"descendant-or-self" "::">
| <"following-sibling" "::">
| <"following" "::">
[65]    AbbrevForwardStep    ::=    "@"? NodeTest
[66]    ReverseStep    ::=    (ReverseAxis NodeTest) | AbbrevReverseStep
[67]    ReverseAxis    ::=    <"parent" "::">
| <"ancestor" "::">
| <"preceding-sibling" "::">
| <"preceding" "::">
| <"ancestor-or-self" "::">
[68]    AbbrevReverseStep    ::=    ".."
[69]    NodeTest    ::=    KindTest | NameTest
[70]    NameTest    ::=    QName | Wildcard
[71]    Wildcard    ::=    "*"
| <NCName ":" "*">
| <"*" ":" NCName>
/* ws: explicit */
[72]    FilterExpr    ::=    PrimaryExpr PredicateList
[73]    PredicateList    ::=    Predicate*
[74]    Predicate    ::=    "[" Expr "]"
[75]    PrimaryExpr    ::=    Literal | VarRef | ParenthesizedExpr | ContextItemExpr | FunctionCall | Constructor | OrderedExpr | UnorderedExpr
[76]    Literal    ::=    NumericLiteral | StringLiteral
[77]    NumericLiteral    ::=    IntegerLiteral | DecimalLiteral | DoubleLiteral
[78]    VarRef    ::=    "$" VarName
[79]    ParenthesizedExpr    ::=    "(" Expr? ")"
[80]    ContextItemExpr    ::=    "."
[81]    OrderedExpr    ::=    <"ordered" "{"> Expr "}"
[82]    UnorderedExpr    ::=    <"unordered" "{"> Expr "}"
[83]    FunctionCall    ::=    <QName "("> (ExprSingle ("," ExprSingle)*)? ")" /* gn: parens */
/* gn: reserved-function-names */
[84]    Constructor    ::=    DirectConstructor
| ComputedConstructor
[85]    DirectConstructor    ::=    DirElemConstructor
| DirCommentConstructor
| DirPIConstructor
[86]    DirElemConstructor    ::=    "<" QName DirAttributeList ("/>" | (">" DirElemContent* "</" QName S? ">")) /* ws: explicit */
/* gn: lt */
[87]    DirAttributeList    ::=    (S (QName S? "=" S? DirAttributeValue)?)* /* ws: explicit */
[88]    DirAttributeValue    ::=    ('"' (EscapeQuot | QuotAttrValueContent)* '"')
| ("'" (EscapeApos | AposAttrValueContent)* "'")
/* ws: explicit */
[89]    QuotAttrValueContent    ::=    QuotAttrContentChar
| CommonContent
[90]    AposAttrValueContent    ::=    AposAttrContentChar
| CommonContent
[91]    DirElemContent    ::=    DirectConstructor
| ElementContentChar
| CDataSection
| CommonContent
[92]    CommonContent    ::=    PredefinedEntityRef | CharRef | "{{" | "}}" | EnclosedExpr
[93]    DirCommentConstructor    ::=    "<!--" DirCommentContents "-->" /* ws: explicit */
[94]    DirCommentContents    ::=    ((Char - '-') | <'-' (Char - '-')>)* /* ws: explicit */
[95]    DirPIConstructor    ::=    "<?" PITarget (S DirPIContents)? "?>" /* ws: explicit */
[96]    DirPIContents    ::=    (Char* - (Char* '?>' Char*)) /* ws: explicit */
[97]    CDataSection    ::=    "<![CDATA[" CDataSectionContents "]]>" /* ws: explicit */
[98]    CDataSectionContents    ::=    (Char* - (Char* ']]>' Char*)) /* ws: explicit */
[99]    ComputedConstructor    ::=    CompDocConstructor
| CompElemConstructor
| CompAttrConstructor
| CompTextConstructor
| CompCommentConstructor
| CompPIConstructor
[100]    CompDocConstructor    ::=    <"document" "{"> Expr "}"
[101]    CompElemConstructor    ::=    (<"element" QName "{"> | (<"element" "{"> Expr "}" "{")) CompElemBody? "}"
[102]    CompElemBody    ::=    (LocalNamespaceDecl | ExprSingle) ("," (LocalNamespaceDecl | ExprSingle))*
[103]    LocalNamespaceDecl    ::=    "namespace" NCName? "{" StringLiteral "}"
[104]    CompAttrConstructor    ::=    (<"attribute" QName "{"> | (<"attribute" "{"> Expr "}" "{")) Expr? "}"
[105]    CompTextConstructor    ::=    <"text" "{"> Expr "}"
[106]    CompCommentConstructor    ::=    <"comment" "{"> Expr "}"
[107]    CompPIConstructor    ::=    (<"processing-instruction" NCName "{"> | (<"processing-instruction" "{"> Expr "}" "{")) Expr? "}"
[108]    SingleType    ::=    AtomicType "?"?
[109]    TypeDeclaration    ::=    "as" SequenceType
[110]    SequenceType    ::=    (ItemType OccurrenceIndicator?)
| <"empty" "(" ")">
[111]    OccurrenceIndicator    ::=    "?" | "*" | "+"
[112]    ItemType    ::=    AtomicType | KindTest | <"item" "(" ")">
[113]    AtomicType    ::=    QName
[114]    KindTest    ::=    DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| AnyKindTest
[115]    AnyKindTest    ::=    <"node" "("> ")"
[116]    DocumentTest    ::=    <"document-node" "("> (ElementTest | SchemaElementTest)? ")"
[117]    TextTest    ::=    <"text" "("> ")"
[118]    CommentTest    ::=    <"comment" "("> ")"
[119]    PITest    ::=    <"processing-instruction" "("> (NCName | StringLiteral)? ")"
[120]    AttributeTest    ::=    <"attribute" "("> (AttribNameOrWildcard ("," TypeName)?)? ")"
[121]    AttribNameOrWildcard    ::=    AttributeName | "*"
[122]    SchemaAttributeTest    ::=    <"schema-attribute" "("> AttributeDeclaration ")"
[123]    AttributeDeclaration    ::=    AttributeName
[124]    ElementTest    ::=    <"element" "("> (ElementNameOrWildcard ("," TypeName "?"?)?)? ")"
[125]    ElementNameOrWildcard    ::=    ElementName | "*"
[126]    SchemaElementTest    ::=    <"schema-element" "("> ElementDeclaration ")"
[127]    ElementDeclaration    ::=    ElementName
[128]    AttributeName    ::=    QName
[129]    ElementName    ::=    QName
[130]    TypeName    ::=    QName
[131]    IntegerLiteral    ::=    Digits
[132]    DecimalLiteral    ::=    ("." Digits) | (Digits "." [0-9]*) /* ws: explicit */
[133]    DoubleLiteral    ::=    (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits /* ws: explicit */
[134]    StringLiteral    ::=    ('"' (PredefinedEntityRef | CharRef | ('"' '"') | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | ("'" "'") | [^'&])* "'") /* ws: explicit */
[135]    PITarget    ::=    [http://www.w3.org/TR/REC-xml#NT-PITarget]XML /* gn: xml-version */
[136]    VarName    ::=    QName
[137]    ValidationMode    ::=    "lax" | "strict"
[138]    Digits    ::=    [0-9]+
[139]    PredefinedEntityRef    ::=    "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" /* ws: explicit */
[140]    CharRef    ::=    [http://www.w3.org/TR/REC-xml#NT-CharRef]XML /* gn: xml-version */
[141]    EscapeQuot    ::=    '""'
[142]    EscapeApos    ::=    "''"
[143]    ElementContentChar    ::=    Char - [{}<&] - [{}<&]
[144]    QuotAttrContentChar    ::=    Char - ["{}<&] - ["{}<&]
[145]    AposAttrContentChar    ::=    Char - ['{}<&] - ['{}<&]
[146]    Pragma    ::=    "(::" S? "pragma" S QName (S ExtensionContents)? "::)" /* ws: explicit */
[147]    MUExtension    ::=    "(::" S? "extension" S QName (S ExtensionContents)? "::)" /* ws: explicit */
[148]    ExtensionContents    ::=    (Char* - (Char* '::)' Char*))
[149]    Comment    ::=    "(:" (CommentContents | Comment)* ":)" /* ws: explicit */
/* gn: comments */
[150]    CommentContents    ::=    (Char+ - (Char* ':)' Char*))
[151]    QName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-QName]Names /* gn: xml-version */
[152]    NCName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-NCName]Names /* gn: xml-version */
[153]    S    ::=    [http://www.w3.org/TR/REC-xml#NT-S]XML /* gn: xml-version */
[154]    Char    ::=    [http://www.w3.org/TR/REC-xml#NT-Char]XML /* gn: xml-version */

The following term definitions will be helpful in defining precisely this exposition.

[Definition: Each rule in the grammar defines one symbol, in the form]

symbol ::= expression

[Definition: A terminal is a single unit of the grammar that can not be further subdivided, and is specified in the EBNF by a character or characters in quotes, or a regular expression.] The following expressions are used to match strings of one or more characters in a terminal:

#xN

where N is a hexadecimal integer, the expression matches the character in ISO/IEC 10646 whose canonical (UCS-4) code value, when interpreted as an unsigned binary number, has the value indicated. The number of leading zeros in the #xN form is insignificant; the number of leading zeros in the corresponding code value is governed by the character encoding in use and is not significant for XML.

[a-zA-Z], [#xN-#xN]

matches any Char with a value in the range(s) indicated (inclusive).

[abc], [#xN#xN#xN]

matches any Char with a value among the characters enumerated. Enumerations and ranges can be mixed in one set of brackets.

[^a-z], [^#xN-#xN]

matches any Char with a value outside the range indicated.

[^abc], [^#xN#xN#xN]

matches any Char with a value not among the characters given. Enumerations and ranges of forbidden values can be mixed in one set of brackets.

"string"

matches a literal string matching that given inside the double quotes.

'string'

matches a literal string matching that given inside the single quotes.

[http://example.org/TR/REC-example/#NT-Example]

matches a production defined in the external specification as per the provided reference. For the purposes of this secification, the entire unit is defined as a terminal.

[Definition: A production combines symbols to form more complex patterns. ] The following productions serve as examples, where A and B represent simple expressions:

(expression)

expression is treated as a unit and may be combined as described in this list.

A?

matches A or nothing; optional A.

A B

matches A followed by B. This operator has higher precedence than alternation; thus A B | C D is identical to (A B) | (C D).

A | B

matches A or B but not both.

A - B

matches any string that matches A but does not match B.

A+

matches one or more occurrences of A.Concatenation has higher precedence than alternation; thus A+ | B+ is identical to (A+) | (B+).

A*

matches zero or more occurrences of A. Concatenation has higher precedence than alternation; thus A* | B* is identical to (A*) | (B*)

A.1.1 Grammar Notes

This section contains general notes on the EBNF productions, which may be helpful in understanding how to create a parser based on this EBNF, how to read the EBNF, and generally call out issues with the syntax. The notes below are referenced from the right side of the production, with the notation: /* gn: <id> */.

grammar-note: parens

A look-ahead of one character is required to distinguish function patterns from a QName or keyword followed by a Pragma, MUExtension or Comment. For example: address (: this may be empty :) may be mistaken for a call to a function named "address" unless this lookahead is employed. Another example is for (: whom the bell :) $tolls = 3 return $tolls, where the keyword "for" must not be mistaken for a function name.

grammar-note: lt

Token disambiguation of the overloaded "<" pattern is defined in terms of positional lexical states. The "<" comparison operator can not occur in the same places as a "<" tag open pattern. The "<" comparison operator can only occur in the OPERATOR state and the "<" tag open pattern can only occur in the DEFAULT and the ELEMENT_CONTENT states. (These states are only a specification tool, and do not mandate an implementation strategy for this same effect.)

grammar-note: validate

The ValidateExpr in the exposition, which does not use the "< ... >" token grouping, presents the production in a much simplified, and understandable, form. The ValidateExpr presented in the appendix is technically correct, but structurally hard to understand, because of limitations of the "< ... >" token grouping.

grammar-note: leading-lone-slash

The "/" presents an issue because it occurs either as a stand alone unit or as a leading prefix that expects a pattern that will be recognized in the DEFAULT state to follow such as a QName or "*". Both of these patterns also may occur as patterns which are recognized in the OPERATOR state. Thus, expressions such as "/ * 5" can easily be confused with the path expression "/*". Therefore, a stand-alone slash on the right hand side of an operator, will need to be parenthesized in order to stand alone, as in "(/) * 5". "5 * /", on the other hand, is legal syntax.

grammar-note: comments

Expression comments are allowed inside expressions everywhere that ignorable whitespace is allowed. Note that expression comments are not allowed in constructor content.

Comments can nest within each other, as long as all "(:" and ":)" patterns are balanced, no matter where they occur within the outer comment.

Note:

Lexical analysis may typically handle nested comments by incrementing a counter for each "(:" pattern, and decrementing the counter for each ":)" pattern. The comment does not terminate until the counter is back to zero.

Following are some illustrative examples:

  • for (: set up loop :) $i in $x return $i will parse correctly, ignoring the comment.

  • 5 instance (: strange place for a comment :) of xs:integer will also parse correctly, ignoring the comment.

  • <eg (: an example:)> $i//title </eg> will cause a syntax error.

  • <eg> (: an example:) </eg> will parse correctly, but characters inside the element is element content, and not an expression comment.

See Comments, Pragmas and Extensions for further information and examples.

grammar-note: xml-version

An implementation's choice to support the [XML 1.0] and [XML Names], or [XML 1.1] and [XML Names 1.1] lexical specification determines the external document from which to obtain the definition for this production. For convenience, XML 1.0 references are always used. In some cases, the XML 1.0 and XML 1.1 definitions may be exactly the same. Also please note that these external productions follow the whitespace rules of their respective specifications, and not the rules of this specification, in particular A.2.2.1 Default Whitespace Handling. Thus prefix : localname is not a valid QName for purposes of this specification, just as it is not permitted in a textual XML document. Also, comments are not permissible on either side of the colon.

grammar-note: reserved-function-names

Some unprefixed function names may be confused with expression syntax by the parser. For instance, if(foo) could either be a function name invocation or an incomplete IfExpr. Therefore it is not legal syntax for a user to invoke functions with these names. See A.3 Reserved Function Names for a list of these names.

A.2 Lexical structure

It is implementation-defined whether the lexical rules of [XML 1.0] and [XML Names]are followed, or alternatively, the lexical rules of [XML 1.1] and [XML Names 1.1] are followed.

Note:

Implementations that support the full [XML 1.1] character set may wish, for purposes of interoperability, to provide a mode that follows only the [XML 1.0] and [XML Names] lexical rules.

When patterns are simple string matches, the strings are embedded directly into the EBNF. In other cases, named terminals are used.

It is up to an implementation to decide on the exact tokenization strategy, which may be different depending on the parser construction. In the EBNF, the notation "< ... >" is used to indicate a grouping of terminals that together may help disambiguate the individual symbols.

This document uses lexical states to assist with terminal symbol recognition. The states specify lexical constraints and transitions based on grammatical positioning. The rules for calculating these states are given in the A.2.4 Lexical Rules section. The specification of these states in this document does not imply any tokenization strategy on the part of implementations.

When tokenizing, the longest possible match that is valid in the current lexical state is preferred .

All keywords are case sensitive. Keywords are not reserved—that is, any QName may duplicate a keyword except as noted in A.3 Reserved Function Names.

A.2.1 Terminal Types

The entire set of terminals in XQuery 1.0 may be divided into two major classes, those that can act as token delimiters, and those that can not.

[Definition: A delimiting terminal may delimit adjacent non-delimiting terminals. Delimiting terminals are only recognized in the appropriate lexical states as specificed by A.2.4 Lexical Rules. ] The following is the list of delimiting terminals:

"<?", "?>", "::", "*", "$", "?", ")", "(", "{", ":", "/", "//", "=", "!=", "<=", "<<", ">=", ">>", ":=", "<", ">", "-", "+", "|", "@", "[", "]", ",", ";", "%%%", """, ".", "..", "<![CDATA[", "]]>", PredefinedEntityRef, CharRef, "/>", "</", "{{", "}}", EscapeQuot, EscapeApos, "'", Pragma, "(::", "::)", Comment, "(:", ":)", "<!--", "-->", S, "}"

[Definition: Non-delimiting terminals generally start and end with alphabetic characters or digits. Adjacent non-delimiting terminals must be delimited by a delimiting terminal. Non-delimiting terminals are only recognized in the appropriate lexical states as specificed by A.2.4 Lexical Rules. ] The following is the list of non-delimiting terminals:

DecimalLiteral, DoubleLiteral, StringLiteral, "xquery", "version", "at", "module", "namespace", "child", "descendant", "parent", "attribute", "self", "descendant-or-self", "ancestor", "following-sibling", "preceding-sibling", "following", "preceding", "ancestor-or-self", "declare", "function", "ordering", "ordered", "unordered", "external", "or", "and", "div", "idiv", "mod", "in", ValidationMode, "construction", "satisfies", "return", "then", "else", "default", "xmlspace", "base-uri", "preserve", "strip", "to", "where", "collation", "intersect", "union", "except", "as", "case", "instance", "of", "castable", "item", "element", "schema-element", "schema-attribute", "processing-instruction", "comment", "text", "empty", "import", "schema", "is", "eq", "ne", "gt", "ge", "lt", "le", "some", "every", "for", "let", "cast", "treat", "validate", Digits, "document-node", "document", "node", "if", "typeswitch", "order", "by", "stable", "ascending", "descending", "greatest", "least", "variable", ExtensionContents, CommentContents, "pragma", "extension", QName, NCName

A.2.2 Whitespace Rules

A.2.2.1 Default Whitespace Handling

[Definition: Whitespace characters are defined by [http://www.w3.org/TR/REC-xml#NT-S] when these characters occur outside of a StringLiteral.]

[Definition: Unless otherwise specified (see A.2.2.2 ExplicitSpecial Whitespace Handling), Ignorable whitespace may occur between terminals, and is not significant to the parse tree. For readability, whitespace may be used in most expressions even though not explicitly notated in the EBNF. All allowable whitespace that is not explicitly specified in the EBNF is ignorable whitespace, and converse, this term does not apply to whitespace that is explicitly specified. ] Whitespace is allowed before the first token and after the last token of a module. Whitespace is optional between delimiting terminals. Whitespace is required to prevent two adjacent non-delimiting terminal from being (mis-)recognized as one. Comments, Pragmas, and MUExtensions may also act as "whitespace" to prevent two adjacent tokens from being recognized as one.. Some illustrative examples are as follows:

  • foo- foo is a syntax error. "foo-" would be recognized as a QName. The parser would then expect a match in the OPERATOR state for "foo", but would find none.

  • foo -foo parses the same as foo - foo, two QNames separated by a subtraction operator. The parser would match the first "foo" as a QName. The parser would then expect a to match in the OPERATOR state, which is satisfied by "-" (but not "-foo"). The last foo would then be matched as another QName.

  • foo(: This is a comment :)- foo also parses the same as foo - foo. This is because the comment prevents the two adjacent tokens from being recognized as one.

    Editorial note  
    In the current test parser, the above fails. So this may need more investigation.
  • foo-foo parses as a single QName. This is because "-" is a valid character in a QName. When used as an operator after the characters of a name, the "-" must be separated from the name, e.g. by using whitespace or parentheses.

  • 10div 3 results in a syntax error, since the "10" and the "div" would both be non-delimiting terminals and must be separated by delimiting terminals in order to be recognized.

  • 10 div3 also results in a syntax error, since the "div" and the "3" would both be non-delimiting terminals and must be separated by delimiting terminals in order to be recognized.

  • 10div3 also results in a syntax error, since the "10", "div" and the "3" would all be non-delimiting terminals and must be separated by delimiting terminals in order to be recognized.

A.2.2.2 Explicit Whitespace Handling

Explict whitespace notation is specified with the EBNF productions, when it is different from the default rules, as follows. These notations do not inherit. In other words, if EBNF rule is marked as /* ws: explicit */, the rule does not automatically apply to all the 'child' EBNF productions of that rule.

ws:explicit

"ws: explicit" means that the EBNF notation S explicitly notates where whitespace is allowed. In productions with this notation, A.2.2.1 Default Whitespace Handling does not apply. Comments, Pragmas, and MUExtensions are also not allowed in these productions.

Whitespace is not freely allowed in the direct Constructor productions, but is specified explicitly in the grammar, in order to be more consistent with XML.

A.2.3 Comments, Pragmas and Extensions

Pragmas and MUExtensions may be used anywhere that ignorable whitespace is allowed. Within a Pragma or MUExtension, the extension content may consist of any sequence of characters that does not include the sequence "::)". Pragmas, and MUExtensions are not allowed to nest. Comments are allowed to nest, though the content of a comment must have balanced comment delimiters without regard to structure. Some illustrative examples:

  • (: is this a comment? ::) is a legal Comment.

  • (: can I comment out a (:: pragma foo ::) like this? :) is a legal Comment. The inner pragma is seen as a nested comment in this case.

  • (: is this a comment? ::) or an error? :) must produce a syntax error. Any unbalanced nesting of "(:" and ":)" will result in an error.

  • (: what about a partial (:: pragma? :) must produce a syntax error. Any unbalanced nesting of "(:" and ":)" will result in an error.

  • (:: pragma foo with a comment (: is this ok? :) or not ::) is a legal Pragma. The inner "comment" is seen as part of the extension content in this case.

  • (:: pragma foo with a comment (: is this a comment? ::) or an error? :) ::) is a syntax error. "::)" patterns are not allowed inside pragma's and extensions.

  • (:: pragma foo with a comment (: what about a partial (:: pragma? :) ::) is a legal Pragma. The inner "comment" and "(::" are seen as part of the extension content in this case.

  • (: commenting out a (: comment :) may be confusing, but often helpful :) is a legal Comment, since balanced nesting of comments is allowed.

  • "this is just a string :)" is a legal expression. However, (: "this is just a string :)" :) will cause a syntax error. Likewise, "this is another string (:" is a legal expression, but (: "this is another string (:" :) will cause a syntax error. It is a limitation of nested comments that literal content can cause unbalanced nesting of comments.

A.2.4 Lexical Rules

The lexical contexts and transitions between lexical contexts is described in terms of a series of states and transitions between those states.

[Definition: A lexical state is a condition where a defined set of patterns are recognized.] The tables below define the complete lexical rules for XQuery. Each two column table corresponds to a lexical state and lists in the first column the tokens thatare recognized when in that state. Any token not listed should result in a syntax error when in that state. When a given token is recognized in the given state, the transition to the next state and/or a lexical action is given in the right column. [Definition: A lexical action is an action that occurs as an side-effect of a pattern recognition.] Following are a list of lexical actions used in the tables:

pushState()

The current state, before the transition, is pushed onto an abstract stack.

pushState(STATE)

A STATE parameter is pushed onto an abstract stack.

popState()

The most recently pushed state is removed from the top of the stack, and becomes the current state.

input_stream.backup(n)

This is a special action that backs up the character stream by n characters. See the description of the OCCURRENCEINDICATOR state for more information.

(maintain state)

This simply means that the current state is maintained with no modification.

The lexical states have, in many cases, close connection to the parser productions. However, just because a token is recognized in a certain lexical state, does not mean it will be legal in the current EBNF production.

The lexical states where whitespace has explicit specification are as follows: START_TAG, END_TAG, ELEMENT_CONTENT, XML_COMMENT, PROCESSING_INSTRUCTION, PROCESSING_INSTRUCTION_CONTENT, CDATA_SECTION, QUOT_ATTRIBUTE_CONTENT, and APOS_ATTRIBUTE_CONTENT.

Note:

There is no requirement for a lexer/parser to be implemented in terms of lexical states—these are only a way to specify the behavior. The only requirement is to produce results that are consistent with the results of these tables.

The DEFAULT State

This state is for patterns that occur at the beginning of an expression or subexpression.

Pattern Transition To State
DecimalLiteral, "..", ".", DoubleLiteral, IntegerLiteral, NotNumber, <NCName ":" "*">, QName, ")", <"*" ":" NCName>, "*", StringLiteral, <"declare" "construction">, <"declare" "ordering">
OPERATOR
<"declare" "default" "collation">, <"declare" "namespace">, <"declare" "base-uri">, <"module" "namespace">
NAMESPACEDECL
<"declare" "default" "element">, <"declare" "default" "function">, <"import" "schema">, <"import" "module">
NAMESPACEKEYWORD
"$", <"for" "$">, <"let" "$">, <"some" "$">, <"every" "$">
VARNAME
<"declare" "variable" "$">
VARNAME
<")" "as">
ITEMTYPE
<"element" "(">, <"attribute" "(">, <"schema-element" "(">, <"schema-attribute" "(">, <"comment" "(">, <"text" "(">, <"node" "(">, <"document-node" "(">
pushState(OPERATOR)
KINDTEST
<"processing-instruction" "(">
pushState(OPERATOR)
KINDTESTFORPI
"<!--"
pushState(OPERATOR)
XML_COMMENT
"<?"
pushState(OPERATOR)
PROCESSING_INSTRUCTION
"<![CDATA["
pushState(OPERATOR)
CDATA_SECTION
"<"
pushState(OPERATOR)
START_TAG
<"declare" "xmlspace">
XMLSPACE_DECL
"}"
popState()
<"validate" "{">, <"validate" ValidationMode>
pushState(OPERATOR)
DEFAULT
<"typeswitch" "(">
DEFAULT
<"element" "{">, <"attribute" "{">
pushState(OPERATOR);pushState(DEFAULT)
<"attribute" QName "{">, "namespace" NCName? "{", <"element" QName "{">, <"document" "{">, <"text" "{">, <"processing-instruction" "{">, <"processing-instruction" NCName "{">, <"comment" "{">
pushState(OPERATOR)
<"declare" "function">
DEFAULT
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY
";"
DEFAULT
"{", <"ordered" "{">, <"unordered" "{">
pushState(OPERATOR)
DEFAULT
<"xquery" "version" StringLiteral>, <"at" StringLiteral>, "@", <"ancestor-or-self" "::">, <"ancestor" "::">, <"attribute" "::">, <"child" "::">, <"descendant-or-self" "::">, <"descendant" "::">, <"following-sibling" "::">, <"following" "::">, <"parent" "::">, <"preceding-sibling" "::">, <"preceding" "::">, <"self" "::">, ",", <"if" "(">, "(", "-", "+", <QName "(">, "//", "/"
(maintain state)


The OPERATOR State

This state is for patterns that are defined for operators.

Pattern Transition To State
"{"
pushState(OPERATOR)
DEFAULT
";", "then", "else", "external", "and", "at", ":=", ",", "div", "=", "except", "eq", "ge", "gt", "le", "lt", "ne", ">=", ">>", ">", "idiv", "intersect", "in", "is", "[", "<=", "<<", "<", "-", "mod", "*", "!=", <"order" "by">, <"stable" "order" "by">, "or", "+", "return", "satisfies", "//", "/", "to", "union", "|", "where", ("preserve" | "strip"), "ordered", "unordered"
DEFAULT
<"castable" "as">, <"cast" "as">
SINGLETYPE
<"instance" "of">, <"treat" "as">, "case", "as", <")" "as">
ITEMTYPE
"}"
popState()
"$", <"for" "$">, <"let" "$">
VARNAME
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY
"?", "]", "collation", ")", "ascending", "descending", <"empty" "greatest">, <"empty" "least">, StringLiteral, "default", NotOperatorKeyword
(maintain state)


The NAMESPACEDECL State

This state occurs inside of a namespace declaration, and is needed to recognize a NCName that is to be used as the prefix, as opposed to allowing a QName to occur. (Otherwise, the difference between NCName and QName are ambiguous.)

Pattern Transition To State
StringLiteral
DEFAULT
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY
"=", NCName
(maintain state)


The NAMESPACEKEYWORD State

This state occurs at places where the keyword "namespace" is expected, which would otherwise be ambiguous compared to a QName. QNames can not occur in this state.

Pattern Transition To State
StringLiteral
DEFAULT
"namespace"
NAMESPACEDECL
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY
<"default" "element">
(maintain state)


The XMLSPACE_DECL State

This state occurs at places where the keywords "preserve" and "strip" is expected to support "declare xmlspace". QNames can not occur in this state.

Pattern Transition To State
"preserve", "strip"
DEFAULT
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY


The SINGLETYPE State

This state distinguishes tokens that can occur only inside the SingleType production.

Pattern Transition To State
QName
OPERATOR
"(:"
pushState()
EXPR_COMMENT


The ITEMTYPE State

This state distinguishes tokens that can occur only inside the ItemType production.

Pattern Transition To State
"$"
VARNAME
<"empty" "(" ")">
OPERATOR
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY
<"element" "(">, <"attribute" "(">, <"schema-element" "(">, <"schema-attribute" "(">, <"comment" "(">, <"text" "(">, <"node" "(">, <"document-node" "(">
pushState(OCCURRENCEINDICATOR)
KINDTEST
<"processing-instruction" "(">
pushState(OCCURRENCEINDICATOR)
KINDTESTFORPI
QName, <"item" "(" ")">
OCCURRENCEINDICATOR
";", "then", "else"
DEFAULT
"external", "and", <"at" StringLiteral>, "at", ":=", ",", "div", "=", "except", "eq", "ge", "gt", "le", "lt", "ne", ">=", ">>", ">", "idiv", "intersect", "in", "is", "[", "(", "<=", "<<", "<", "-", "mod", "!=", <"order" "by">, <"stable" "order" "by">, "or", "return", "satisfies", "to", "union", "|", "where"
DEFAULT
<"castable" "as">, <"cast" "as">
SINGLETYPE
<"instance" "of">, <"treat" "as">, "case", "as", <")" "as">
ITEMTYPE


The KINDTEST State
Pattern Transition To State
"{"
pushState(OPERATOR)
DEFAULT
")"
popState()
"*", QName
CLOSEKINDTEST
<"element" "(">, <"schema-element" "(">
pushState(KINDTEST)
KINDTEST
"(:"
pushState()
EXPR_COMMENT


The KINDTESTFORPI State
Pattern Transition To State
")"
popState()
"(:"
pushState()
EXPR_COMMENT
NCName, StringLiteral
(maintain state)


The CLOSEKINDTEST State
Pattern Transition To State
")"
popState()
","
KINDTEST
"{"
pushState(OPERATOR)
DEFAULT
"?"
(maintain state)
"(:"
pushState()
EXPR_COMMENT


The OCCURRENCEINDICATOR State

This special state is needed to distinguish occurrence indicators that appear in the SequenceType production. For instance, compare "foo instance of baz*" to "baz*foo". In the first case, the "*" is interpreted as an occurrence indicator, and in the second case, it must be interpreted as a multiplication operator. But, when in the OCCURRENCEINDICATOR state, if anything else other than "?", "*", and "+", those symbols must be interpreted in the OPERATOR state. For instance, this would occur with the expression "foo instance of baz and $x", with the operator "and". This backing up of the lexical characters in order to reset the state, is symbolized by the notation "input_stream.backup(1)". NotOccurrenceIndicator is a special symbol for any character that is not an occurrence indicator.

Pattern Transition To State
[NotOccurrenceIndicator]
input_stream.backup(1)
OPERATOR
"?", "*", "+"
OPERATOR
"(:"
pushState()
EXPR_COMMENT


The VARNAME State

This state differentiates variable names from qualified names. This allows only the pattern of a QName to be recognized when otherwise ambiguities could occur.

Pattern Transition To State
VarName
OPERATOR
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY


The START_TAG State

This state allows attributes in the native XML syntax, and marks the beginning of an element construction. Element constructors also push the current state, popping it at the conclusion of an end tag. In the START_TAG state, the string ">" is recognized as a token which is associated with the transition to the original state.

Pattern Transition To State
"/>"
popState()
">"
ELEMENT_CONTENT
'"'
QUOT_ATTRIBUTE_CONTENT
"'"
APOS_ATTRIBUTE_CONTENT
S, QName, "="
(maintain state)


The ELEMENT_CONTENT State

This state allows XML-like content, without these characters being misinterpreted as expressions. The character "{" marks a transition to the DEFAULT state, i.e. the start of an embedded expression, and the "}" character pops back to the ELEMENT_CONTENT state. To allow curly braces to be used as character content, a double left or right curly brace is interpreted as a single curly brace character. The string "</" is interpreted as the beginning of an end tag, which is associated with a transition to the END_TAG state.

Pattern Transition To State
"</"
END_TAG
"{"
pushState()
DEFAULT
"<!--"
pushState()
XML_COMMENT
"<?"
pushState()
PROCESSING_INSTRUCTION
"<![CDATA["
pushState()
CDATA_SECTION
"<"
pushState()
START_TAG
PredefinedEntityRef, CharRef, "{{", "}}", ElementContentChar
(maintain state)


The END_TAG State

When the end tag is terminated, the state is popped to the state that was pushed at the start of the corresponding start tag.

Pattern Transition To State
">"
popState()
S, QName
(maintain state)


The XML_COMMENT State

The "<--" token marks the beginning of an XML Comment, and the "-->" token marks the end. This allows no special interpretation of other characters in this state.

Pattern Transition To State
"-->"
popState()
(Char - '-'), <'-' (Char - '-')>
(maintain state)


The EXPR_COMMENT State

The "(:" token marks the beginning of an expression Comment, and the ":)" token marks the end. This allows no special interpretation of other characters in this state.

Pattern Transition To State
":)"
popState()
"(:"
pushState()
EXPR_COMMENT
"(::"
pushState()
EXT_KEY
Char
(maintain state)


The EXT_CONTENT State

This state occurs for the content of must-understand extension.

Pattern Transition To State
"::)"
popState()
Char, S
(maintain state)


The EXT_KEY State

The "(::" token marks the beginning of an expression extension, which must be followed by a keyword.

Pattern Transition To State
"pragma", "extension"
EXT_NAME
S
(maintain state)


The EXT_NAME State

This state recognizes extension names and transitions to the extension content state.

Pattern Transition To State
QName
EXT_CONTENT
S
(maintain state)


The PROCESSING_INSTRUCTION State

In this state, only patterns that are legal in a processing instruction name are recognized.

Pattern Transition To State
S
PROCESSING_INSTRUCTION_CONTENT
"?>"
popState()
PITarget
(maintain state)


The PROCESSING_INSTRUCTION_CONTENT State

In this state, only characters are that are legal in processing instruction content are recognized.

Pattern Transition To State
"?>"
popState()
Char
(maintain state)


The CDATA_SECTION State

In this state, only lexemes that are legal in a CDATA section are recognized.

Pattern Transition To State
"]]>"
popState()
Char
(maintain state)


The QUOT_ATTRIBUTE_CONTENT State

This state allows content legal for attributes. The character "{" marks a transition to the DEFAULT state, i.e. the start of an embedded expression, and the "}" character pops back to the original state. To allow curly braces to be used as character content, a double left or right curly brace is interpreted as a single curly brace character. This state is the same as APOS_ATTRIBUTE_CONTENT, except that apostrophes are allowed without escaping, and an unescaped quote marks the end of the state.

Pattern Transition To State
'"'
START_TAG
"{"
pushState()
DEFAULT
EscapeQuot, PredefinedEntityRef, CharRef, "{{", "}}", QuotAttrContentChar
(maintain state)


The APOS_ATTRIBUTE_CONTENT State

This state is the same as QUOT_ATTRIBUTE_CONTENT, except that quotes are allowed, and an unescaped apostrophe marks the end of the state.

Pattern Transition To State
"'"
START_TAG
"{"
pushState()
DEFAULT
EscapeApos, PredefinedEntityRef, CharRef, "{{", "}}", AposAttrContentChar
(maintain state)


A.3 Reserved Function Names

The following is a list of names that must not be used as user function names in an unprefixed form, because these functions could be confused with expression syntax. Users should not have unprefixed invocations of functions with these names, and if they want to protect themselves from future changes they should use the prefixed form, or put a distinctive string in their function names.

  • attribute

  • comment

  • document-node

  • element

  • empty

  • if

  • item

  • node

  • processing-instruction

  • text

  • type

  • typeswitch

A.4 Precedence Order

The grammar defines built-in precedence, which is summarised here. Operators that have a lower precedence number can not be contained by operators with a higher precedence number. Operators may contain other operators with the same precedence number on the right-hand-side. In the cases where a number of operators are at the same precedence level, the operators are applied from left to right.

The operators in order of increasing precedence are:

1 (comma)
2 for, some, every, typeswitch, if
3 or
4 and
5 eq, ne, lt, le, gt, ge, =, !=, <, <=, >, >=, is, <<, >>
6 to
7 +, -
8 *, div, idiv, mod
9 -(unary), +(unary)
10 union, |
11 intersect, except
12 instance of
13 treat
14 castable
15 cast
16 validate, /, //
17 [ ], ( )

B Type Promotion and Operator Mapping

B.1 Type Promotion

[Definition: Under certain circumstances, an atomic value can be promoted from one type to another. Type promotion is used in function calls (see 3.1.5 Function Calls) and in processing of operators that accept numeric operands (see B.2 Operator Mapping).] The following type promotions are permitted:

  1. A value of type xs:float (or any type derived by restriction from xs:float) can be promoted to the type xs:double. The result is the xs:double value that is the same as the original value.

  2. A value of type xs:decimal (or any type derived by restriction from xs:decimal) can be promoted to either of the types xs:float or xs:double. The result of this promotion is created by casting the original value to the required type. This kind of promotion may cause loss of precision.

Note that type promotion is different from subtype substitution. For example:

  • A function that expects a parameter $p of type xs:float can be invoked with a value of type xs:decimal. This is an example of type promotion. The value is actually converted to the expected type. Within the body of the function, $p instance of xs:decimal returns false.

  • A function that expects a parameter $p of type xs:decimal can be invoked with a value of type xs:integer. This is an example of subtype substitution. The value retains its original type. Within the body of the function, $p instance of xs:integer returns true.

B.2 Operator Mapping

The tables in this section list the combinations of types for which the various operators of XQuery are defined in terms of functions that are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The and and or operators are defined directly in the main body of this document, and do not occur in this table. For each valid combination of types, the table indicates the function(s) that are used to implement the operator and the type of the result. Note that in some cases the function does not implement the full semantics of the given operator. For the definition of each operator (including its behavior for empty sequences or sequences of length greater than one), see the descriptive material in the main part of this document.

Any operator listed in the tables may be validly applied to an operand of type AT if the table calls for an operand of type ET and type-matches(ET, AT) is true (see 2.4.4 SequenceType Matching). For example, a table entry indicates that the gt operator may be applied to two xs:date operands, returning xs:boolean. Therefore, the gt operator may also be applied to two (possibly different) subtypes of xs:date, also returning xs:boolean.

In the operator tables, the term numeric refers to the types xs:integer, xs:decimal, xs:float, and xs:double. An operator whose operands and result are designated as numeric might be thought of as representing four operators, one for each of the numeric types. For example, the numeric + operator might be thought of as representing the following four operators:

Operator First operand type Second operand type Result type
+ xs:integer xs:integer xs:integer
+ xs:decimal xs:decimal xs:decimal
+ xs:float xs:float xs:float
+ xs:double xs:double xs:double

A numeric operator may be validly applied to an operand of type AT if type-matches(ET, AT) is true where ET is any of the four numeric types. If the result type of an operator is listed as numeric, it means "the first type in the ordered list (xs:integer, xs:decimal, xs:float, xs:double) into which all operands can be converted by subtype substitution and type promotion." As an example, suppose that the type hatsize is derived from xs:integer and the type shoesize is derived from xs:float. Then if the + operator is invoked with operands of type hatsize and shoesize, it returns a result of type xs:float. Similarly, if + is invoked with two operands of type hatsize it returns a result of type xs:integer.

In the following tables, the term Gregorian refers to the types xs:gYearMonth, xs:gYear, xs:gMonthDay, xs:gDay, and xs:gMonth. For binary operators that accept two Gregorian-type operands, both operands must have the same type (for example, if one operand is of type xs:gDay, the other operand must be of type xs:gDay.)

Binary Operators
Operator Type(A) Type(B) Function Result type
A + B numeric numeric op:numeric-add(A, B) numeric
A + B xs:date xdt:yearMonthDuration op:add-yearMonthDuration-to-date(A, B) xs:date
A + B xdt:yearMonthDuration xs:date op:add-yearMonthDuration-to-date(B, A) xs:date
A + B xs:date xdt:dayTimeDuration op:add-dayTimeDuration-to-date(A, B) xs:date
A + B xdt:dayTimeDuration xs:date op:add-dayTimeDuration-to-date(B, A) xs:date
A + B xs:time xdt:dayTimeDuration op:add-dayTimeDuration-to-time(A, B) xs:time
A + B xdt:dayTimeDuration xs:time op:add-dayTimeDuration-to-time(B, A) xs:time
A + B xs:datetime xdt:yearMonthDuration op:add-yearMonthDuration-to-dateTime(A, B) xs:dateTime
A + B xdt:yearMonthDuration xs:datetime op:add-yearMonthDuration-to-dateTime(B, A) xs:dateTime
A + B xs:datetime xdt:dayTimeDuration op:add-dayTimeDuration-to-dateTime(A, B) xs:dateTime
A + B xdt:dayTimeDuration xs:datetime op:add-dayTimeDuration-to-dateTime(B, A) xs:dateTime
A + B xdt:yearMonthDuration xdt:yearMonthDuration op:add-yearMonthDurations(A, B) xdt:yearMonthDuration
A + B xdt:dayTimeDuration xdt:dayTimeDuration op:add-dayTimeDurations(A, B) xdt:dayTimeDuration
A - B numeric numeric op:numeric-subtract(A, B) numeric
A - B xs:date xs:date fn:subtract-dates-yielding-dayTimeDuration(A, B) xdt:dayTimeDuration
A - B xs:date xdt:yearMonthDuration op:subtract-yearMonthDuration-from-date(A, B) xs:date
A - B xs:date xdt:dayTimeDuration op:subtract-dayTimeDuration-from-date(A, B) xs:date
A - B xs:time xs:time op:subtract-times(A, B) xdt:dayTimeDuration
A - B xs:time xdt:dayTimeDuration op:subtract-dayTimeDuration-from-time(A, B) xs:time
A - B xs:datetime xs:datetime fn:subtract-dateTimes-yielding-dayTimeDuration(A, B) xdt:dayTimeDuration
A - B xs:datetime xdt:yearMonthDuration op:subtract-yearMonthDuration-from-dateTime(A, B) xs:dateTime
A - B xs:datetime xdt:dayTimeDuration op:subtract-dayTimeDuration-from-dateTime(A, B) xs:dateTime
A - B xdt:yearMonthDuration xdt:yearMonthDuration op:subtract-yearMonthDurations(A, B) xdt:yearMonthDuration
A - B xdt:dayTimeDuration xdt:dayTimeDuration op:subtract-dayTimeDurations(A, B) xdt:dayTimeDuration
A * B numeric numeric op:numeric-multiply(A, B) numeric
A * B xdt:yearMonthDuration numeric op:multiply-yearMonthDuration(A, B) xdt:yearMonthDuration
A * B numeric xdt:yearMonthDuration op:multiply-yearMonthDuration(B, A) xdt:yearMonthDuration
A * B xdt:dayTimeDuration numeric op:multiply-dayTimeDuration(A, B) xdt:dayTimeDuration
A * B numeric xdt:dayTimeDuration op:multiply-dayTimeDuration(B, A) xdt:dayTimeDuration
A idiv B numeric numeric op:integer-div(A, B) xs:integer
A div B numeric numeric op:numeric-divide(A, B) numeric; but xs:decimal if both operands are xs:integer
A div B xdt:yearMonthDuration numeric op:divide-yearMonthDuration(A, B) xdt:yearMonthDuration
A div B xdt:dayTimeDuration numeric op:divide-dayTimeDuration(A, B) xdt:dayTimeDuration
A mod B numeric numeric op:numeric-mod(A, B) numeric
A eq B numeric numeric op:numeric-equal(A, B) xs:boolean
A eq B xs:boolean xs:boolean op:boolean-equal(A, B) xs:boolean
A eq B xs:string xs:string op:numeric-equal(fn:compare(A, B), 1) xs:boolean
A eq B xs:date xs:date op:date-equal(A, B) xs:boolean
A eq B xs:time xs:time op:time-equal(A, B) xs:boolean
A eq B xs:dateTime xs:dateTime op:datetime-equal(A, B) xs:boolean
A eq B xdt:yearMonthDuration xdt:yearMonthDuration op:yearMonthDuration-equal(A, B) xs:boolean
A eq B xdt:dayTimeDuration xdt:dayTimeDuration op:dayTimeDuration-equal(A, B) xs:boolean
A eq B Gregorian Gregorian op:gYear-equal(A, B) etc. xs:boolean
A eq B xs:hexBinary xs:hexBinary op:hex-binary-equal(A, B) xs:boolean
A eq B xs:base64Binary xs:base64Binary op:base64-binary-equal(A, B) xs:boolean
A eq B xs:anyURI xs:anyURI op:anyURI-equal(A, B) xs:boolean
A eq B xs:QName xs:QName op:QName-equal(A, B) xs:boolean
A eq B xs:NOTATION xs:NOTATION op:NOTATION-equal(A, B) xs:boolean
A ne B numeric numeric fn:not(op:numeric-equal(A, B)) xs:boolean
A ne B xs:boolean xs:boolean fn:not(op:boolean-equal(A, B)) xs:boolean
A ne B xs:string xs:string fn:not(op:numeric-equal(fn:compare(A, B), 1)) xs:boolean
A ne B xs:date xs:date fn:not(op:date-equal(A, B)) xs:boolean
A ne B xs:time xs:time fn:not(op:time-equal(A, B)) xs:boolean
A ne B xs:dateTime xs:dateTime fn:not(op:datetime-equal(A, B)) xs:boolean
A ne B xdt:yearMonthDuration xdt:yearMonthDuration fn:not(op:yearMonthDuration-equal(A, B)) xs:boolean
A ne B xdt:dayTimeDuration xdt:dayTimeDuration fn:not(op:dayTimeDuration-equal(A, B) xs:boolean
A ne B Gregorian Gregorian fn:not(op:gYear-equal(A, B)) etc. xs:boolean
A ne B xs:hexBinary xs:hexBinary fn:not(op:hex-binary-equal(A, B)) xs:boolean
A ne B xs:base64Binary xs:base64Binary fn:not(op:base64-binary-equal(A, B)) xs:boolean
A ne B xs:anyURI xs:anyURI fn:not(op:anyURI-equal(A, B)) xs:boolean
A ne B xs:QName xs:QName fn:not(op:QName-equal(A, B)) xs:boolean
A ne B xs:NOTATION xs:NOTATION fn:not(op:NOTATION-equal(A, B)) xs:boolean
A gt B numeric numeric op:numeric-greater-than(A, B) xs:boolean
A gt B xs:boolean xs:boolean op:boolean-greater-than(A, B) xs:boolean
A gt B xs:string xs:string op:numeric-greater-than(fn:compare(A, B), 0) xs:boolean
A gt B xs:date xs:date op:date-greater-than(A, B) xs:boolean
A gt B xs:time xs:time op:time-greater-than(A, B) xs:boolean
A gt B xs:dateTime xs:dateTime op:datetime-greater-than(A, B) xs:boolean
A gt B xdt:yearMonthDuration xdt:yearMonthDuration op:yearMonthDuration-greater-than(A, B) xs:boolean
A gt B xdt:dayTimeDuration xdt:dayTimeDuration op:dayTimeDuration-greater-than(A, B) xs:boolean
A lt B numeric numeric op:numeric-less-than(A, B) xs:boolean
A lt B xs:boolean xs:boolean op:boolean-less-than(A, B) xs:boolean
A lt B xs:string xs:string op:numeric-less-than(fn:compare(A, B), 0) xs:boolean
A lt B xs:date xs:date op:date-less-than(A, B) xs:boolean
A lt B xs:time xs:time op:time-less-than(A, B) xs:boolean
A lt B xs:dateTime xs:dateTime op:datetime-less-than(A, B) xs:boolean
A lt B xdt:yearMonthDuration xdt:yearMonthDuration op:yearMonthDuration-less-than(A, B) xs:boolean
A lt B xdt:dayTimeDuration xdt:dayTimeDuration op:dayTimeDuration-less-than(A, B) xs:boolean
A ge B numeric numeric fn:not(op:numeric-less-than(A, B)) xs:boolean
A ge B xs:boolean xs:boolean fn:not(op:boolean-less-than(A, B))
A ge B xs:string xs:string op:numeric-greater-than(fn:compare(A, B), -1) xs:boolean
A ge B xs:date xs:date fn:not(op:date-less-than(A, B)) xs:boolean
A ge B xs:time xs:time fn:not(op:time-less-than(A, B)) xs:boolean
A ge B xs:dateTime xs:dateTime fn:not(op:datetime-less-than(A, B)) xs:boolean
A ge B xdt:yearMonthDuration xdt:yearMonthDuration fn:not(op:yearMonthDuration-less-than(A, B)) xs:boolean
A ge B xdt:dayTimeDuration xdt:dayTimeDuration fn:not(op:dayTimeDuration-less-than(A, B)) xs:boolean
A le B numeric numeric fn:not(op:numeric-greater-than(A, B)) xs:boolean
A le B xs:boolean xs:boolean fn:not(op:boolean-greater-than(A, B))
A le B xs:string xs:string op:numeric-less-than(fn:compare(A, B), 1) xs:boolean
A le B xs:date xs:date fn:not(op:date-greater-than(A, B)) xs:boolean
A le B xs:time xs:time fn:not(op:time-greater-than(A, B)) xs:boolean
A le B xs:dateTime xs:dateTime fn:not(op:datetime-greater-than(A, B)) xs:boolean
A le B xdt:yearMonthDuration xdt:yearMonthDuration fn:not(op:yearMonthDuration-greater-than(A, B)) xs:boolean
A le B xdt:dayTimeDuration xdt:dayTimeDuration fn:not(op:dayTimeDuration-greater-than(A, B)) xs:boolean
A is B node() node() op:is-same-node(A, B) xs:boolean
A << B node() node() op:node-before(A, B) xs:boolean
A >> B node() node() op:node-after(A, B) xs:boolean
A union B node()* node()* op:union(A, B) node()*
A | B node()* node()* op:union(A, B) node()*
A intersect B node()* node()* op:intersect(A, B) node()*
A except B node()* node()* op:except(A, B) node()*
A to B xs:integer xs:integer op:to(A, B) xs:integer+
A , B item()* item()* op:concatenate(A, B) item()*
Unary Operators
Operator Operand type Function Result type
+ A numeric op:numeric-unary-plus(A) numeric
- A numeric op:numeric-unary-minus(A) numeric

C Context Components

The tables in this section describe how values are assigned to the various components of the static context and dynamic context, and to the parameters that control the serialization process.

C.1 Static Context Components

The following table describes the components of the static context. The following aspects of each component are described:

  • Default value: This is the value of the component if it is not overridden or augmented by the implementation or by a query.

  • Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default value of the component by a different value and/or to augment the default value by additional values.

  • Can be overwritten or augmented by a query: Indicates whether a query is allowed to replace and/or augment the initial value provided by default or by the implementation. If so, indicates how this is accomplished (for example, by a declaration in the prolog).

  • Scope: Indicates where the component is applicable. "Global" indicates that the component applies globally, throughout all the modules used in a query. "Module resource" indicates that the component applies throughout a module resource. "Lexical" indicates that the component applies within the expression in which it is defined (equivalent to "module resource" if the component is declared in a Prolog.)

  • Consistency Rules: Indicates rules that must be observed in assigning values to the component. If any consistency rule is violated, a static error is raised. Additional consistency rules may be found in 2.2.5 Consistency Constraints.

Static Context Components
Component Default predefined value Can be overwritten or augmented by implementation? Can be overwritten or augmented by a query? Scope Consistency rules
XPath 1.0 Compatability Mode false no no global Must be false.
Statically known namespaces fn, xml, xs, xsi, xdt, local overwriteable and augmentable (except for xml) overwriteable and augmentable by prolog or element constructor lexical Only one namespace can be assigned to a given prefix per lexical scope.
Default element/type namespace no namespace overwriteable overwriteable by prolog or element constructor lexical Only one default namespace per lexical scope.
Default function namespace fn overwriteable (not recommended) overwriteable by prolog module resource Only one declaration per prolog.
In-scope type definitions Built-in types in xs, xdt augmentable augmentable by schema import in prolog module resource Only one definition per global or local type.
In-scope element declarations none augmentable augmentable by schema import in prolog module resource Only one definition per global or local element name.
In-scope attribute declarations none augmentable augmentable by schema import in prolog module resource Only one definition per global or local attribute name.
In-scope variables none augmentable overwriteable and augmentable by prolog and by variable-binding expressions lexical Only one definition per variable per lexical scope.
Context item static type none augmentable not explicitly, but can be influenced by expressions lexical None
Function signatures Functions in fn namespace, and constructors for built-in atomic types augmentable augmentable by module import and by function declaration in prolog module resource Each function must have a unique expanded QName and number of arguments.
Statically known collations only the default collation augmentable no module resource Each URI uniquely identifies a collation.
Default collation Unicode codepoint collation overwriteable overwriteable by prolog module resource Only one default collation per module resource.
Construction mode preserve overwriteable overwriteable by prolog module resource Only one construction mode per module resource.
Ordering mode ordered overwriteable overwriteable by prolog or expression lexical None
XMLSpace policy strip overwriteable overwriteable by prolog module resource Only one XMLSpace declaration per module resource.
Base URI none overwriteable overwriteable by prolog module resource Only one base-uri declaration per module resource.
Statically known documents none augmentable no module resource None
Statically known collections none augmentable no module resource None
XQuery Flagger status off overwriteable no global None
XQuery Static Flagger status off overwriteable no global None

C.2 Dynamic Context Components

The following table describes the components of the dynamic context. The following aspects of each component are described:

  • Default value: This is the value of the component if it is not overridden or augmented by the implementation or by a query.

  • Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default value of the component by a different value and/or to augment the default value by additional values.

  • Can be overwritten or augmented by a query: Indicates whether a query is allowed to replace and/or augment the initial value provided by default or by the implementation. If so, indicates how this is accomplished.

  • Scope: Indicates where the component is applicable. "Global" indicates that the component applies globally, throughout all the modules used in a query, and remains constant during evaluation of a query. "Dynamic" indicates that evalation of an expression may influence the value of the component for that expression and for nested expressions.

  • Consistency Rules: Indicates rules that must be observed in assigning values to the component. Additional consistency rules may be found in 2.2.5 Consistency Constraints.

Dynamic Context Components
Component Default predefined value Can be overwritten or augmented by implementation? Can be overwritten or augmented by a query? Scope Consistency rules
Context item none overwriteable overwritten during evaluation of path expressions and predicates dynamic none
Context position none overwriteable overwritten during evaluation of path expressions and predicates dynamic Must be consistent with context item and context size
Context size none overwriteable overwritten during evaluation of path expressions and predicates dynamic Must be consistent with context item
Variable values none augmentable overwriteable and augmentable by prolog and by variable-binding expressions dynamic Names and values must be consistent with in-scope variables.
Function implementations Functions in fn namespace, and constructors for built-in atomic types augmentable augmentable by module import and by function declaration in prolog global Must be consistent with function signatures
Current date and time none Must be initialized by implementation no global Remains constant during evaluation of a query.
Implicit timezone none Must be initialized by implementation no global Remains constant during evaluation of a query.
Available documents none Must be initialized by implementation no global None
Available collections none Must be initialized by implementation no global None

C.3 Serialization Parameters

The following table specifies default values for the parameters that control the process of serializing the Data Model into XML notation (method = "xml"). The meanings of the various parameters are defined in [XSLT 2.0 and XQuery 1.0 Serialization]. For each parameter, an XQuery implementation may (but is not required to) provide a means whereby a user can override the default value.

Serialization Parameters
Parameter Default Value
encoding implementation-defined
cdata-section-elements empty
doctype-system (none)
doctype-public (none)
escape-uri-attributes no
indent no
media-type implementation-defined
normalization-form implementation-defined
omit-xml-declaration yes
standalone none
use-character-maps empty
version 1.0

D References

D.1 Normative References

XQuery 1.0 and XPath 2.0 Functions and Operators
World Wide Web Consortium. XQuery 1.0 and XPath 2.0 Functions and Operators W3C Working Draft, 23 Jul. 2004. See http://www.w3.org/TR/xpath-functions/
XQuery 1.0 and XPath 2.0 Formal Semantics
World Wide Web Consortium. XQuery 1.0 and XPath 2.0 Formal Semantics. W3C Working Draft, 20 Feb. 2004. See http://www.w3.org/TR/xquery-semantics/.
XML Schema
World Wide Web Consortium. XML Schema, Parts 0, 1, and 2. W3C Recommendation, 2 May 2001. See http://www.w3.org/TR/2001/REC-xmlschema-0-20010502/, http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/, and http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/.
XQuery 1.0 and XPath 2.0 Data Model
World Wide Web Consortium. XQuery 1.0 and XPath 2.0 Data Model. W3C Working Draft, 23 Jul. 2004. See http://www.w3.org/TR/xpath-datamodel/.
XSLT 2.0 and XQuery 1.0 Serialization
World Wide Web Consortium. XSLT 2.0 and XQuery 1.0 Serialization. W3C Working Draft, 23 Jul. 2004. See http://www.w3.org/TR/xslt-xquery-serialization/.
XML 1.0
World Wide Web Consortium. Extensible Markup Language (XML) 1.0. W3C Recommendation. See http://www.w3.org/TR/2000/REC-xml-20001006
XML 1.1
World Wide Web Consortium. Extensible Markup Language (XML) 1.1. W3C Recommendation. See http://www.w3.org/TR/xml11/
XML Names
World Wide Web Consortium. Namespaces in XML. W3C Recommendation. See http://www.w3.org/TR/REC-xml-names/
XML Names 1.1
World Wide Web Consortium. Namespaces in XML 1.1. W3C Recommendation. See http://www.w3.org/TR/xml-names11/
ISO/IEC 10646
ISO (International Organization for Standardization). ISO/IEC 10646-1993 (E). Information technology—Universal Multiple-Octet Coded Character Set (UCS)—Part 1: Architecture and Basic Multilingual Plane. [Geneva]: International Organization for Standardization, 1993 (plus amendments AM 1 through AM 7).
ISO/IEC 10646-2000
ISO (International Organization for Standardization). ISO/IEC 10646-1:2000. Information technology—Universal Multiple-Octet Coded Character Set (UCS)—Part 1: Architecture and Basic Multilingual Plane. [Geneva]: International Organization for Standardization, 2000.
Unicode
The Unicode Consortium. The Unicode Standard, Version 2.0. Reading, Mass.: Addison-Wesley Developers Press, 1996.
Unicode3
The Unicode Consortium. The Unicode Standard, Version 3.0. Reading, Mass.: Addison-Wesley Developers Press, 2000. ISBN 0-201-61633-5.

D.2 Non-normative References

XML Query 1.0 Requirements
World Wide Web Consortium. XML Query 1.0 Requirements. W3C Working Draft, 27 Jun 2003. See http://www.w3.org/TR/xquery-requirements/.
XQueryX 1.0
World Wide Web Consortium. XQueryX, Version 1.0. W3C Working Draft, 7 June 2001. See http://www.w3.org/TR/xqueryx
Editorial note  
As of the date of this publication, XQueryX has not incorporated recent language changes; it will be made consistent with this document in its next edition.
XPath 2.0
World Wide Web Consortium. XML Path Language (XPath) Version 2.0. W3C Working Draft, 23 Jul. 2004. See http://www.w3.org/TR/xpath20/
XSLT 2.0
World Wide Web Consortium. XSL Transformations (XSLT) 2.0. W3C Working Draft. See http://www.w3.org/TR/xslt20/
XML Query Use Cases
World Wide Web Consortium. XML Query Use Cases. W3C Working Draft, 12 Nov. 2003. See http://www.w3.org/TR/xquery-use-cases/.
ISO 8601
International Organization for Standardization (ISO). Representations of Dates and Times, 2000-08-03. Available from http://www.iso.ch/
Use Case Sample Queries
Queries from the XQuery 1.0 Use Caes, presented in a single file (See http://www.w3.org/TR/2003/WD-xquery-use-cases-20031112/xquery-use-case-queries.txt.)
XQuery Sample Queries
Queries from this document, presented in a single file. (See http://www.w3.org/TR/2003/WD-xquery-use-cases-20031112/xquery-wd-queries.txt.)

D.3 Non-normative Background References

XQL
J. Robie, J. Lapp, D. Schach. XML Query Language (XQL). See http://www.w3.org/TandS/QL/QL98/pp/xql.html.
XML-QL
Alin Deutsch, Mary Fernandez, Daniela Florescu, Alon Levy, and Dan Suciu. A Query Language for XML. See http://www.research.att.com/~mff/files/final.html
SQL
International Organization for Standardization (ISO). Information Technology-Database Language SQL. Standard No. ISO/IEC 9075:1999. (Available from American National Standards Institute, New York, NY 10036, (212) 642-4900.)
ODMG
Rick Cattell et al. The Object Database Standard: ODMG-93, Release 1.2. Morgan Kaufmann Publishers, San Francisco, 1996.
Lorel
Serge Abiteboul, Dallan Quass, Jason McHugh, Jennifer Widom, and Janet L. Wiener. The Lorel Query Language for Semistructured Data. International Journal on Digital Libraries, 1(1):68-88, April 1997. See "http://www-db.stanford.edu/~widom/pubs.html
YATL
S. Cluet, S. Jacqmin, and J. Simeon. The New YATL: Design and Specifications. Technical Report, INRIA, 1999.
Quilt
Don Chamberlin, Jonathan Robie, and Daniela Florescu. Quilt: an XML Query Language for Heterogeneous Data Sources. In Lecture Notes in Computer Science, Springer-Verlag, Dec. 2000. Also available at http://www.almaden.ibm.com/cs/people/chamberlin/quilt_lncs.pdf. See also http://www.almaden.ibm.com/cs/people/chamberlin/quilt.html.

D.4 Non-normative Informative Material

RFC2396
T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource Identifiers (URI): Generic Syntax. IETF RFC 2396. See http://www.ietf.org/rfc/rfc2396.txt.
Character Model
World Wide Web Consortium. Character Model for the World Wide Web. W3C Working Draft. See http://www.w3.org/TR/charmod/
XML Infoset
World Wide Web Consortium. XML Information Set. W3C Recommendation 24 October 2001. See http://www.w3.org/TR/xml-infoset/
XPath 1.0
World Wide Web Consortium. XML Path Language (XPath) Version 1.0. W3C Recommendation, Nov. 16, 1999. See http://www.w3.org/TR/xpath.html
XPointer
World Wide Web Consortium. XML Pointer Language (XPointer). W3C Last Call Working Draft 8 January 2001. See http://www.w3.org/TR/WD-xptr
XSLT 1.0
World Wide Web Consortium. XSL Transformations (XSLT) 1.0. W3C Recommendation. See http://www.w3.org/TR/xslt

E Glossary

atomic value

An atomic value is a value in the value space of an atomic type, including all the atomic types defined in [XML Schema] and xdt:untypedAtomic.

atomization

Atomization is applied to a value when the value is used in a context in which a sequence of atomic values is required. The result of atomization is either a sequence of atomic values or a type error. Atomization of a sequence is defined as the result of invoking the fn:data function on the sequence, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].

available collections

Available collections. This is a mapping of strings onto sequences of nodes. The string represents the absolute URI of a resource. The sequence of nodes represents the result of the fn:collection function when that URI is supplied as the argument.

available documents

Available documents. This is a mapping of strings onto document nodes. The string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc function when applied to that URI.

base URI

Base URI. This is an absolute URI, used when necessary in the resolution of relative URIs (for example, by the fn:resolve-uri function.)

boundary whitespace

Whitespace characters that occur by themselves in the boundaries between tags and/or enclosed expressions are called boundary whitespace.

computed element constructor

A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.

construction mode

Construction mode. The construction mode governs the behavior of element constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and the attributes and descendants of the constructed element retain their original types. If construction mode is strip, the type of the constructed element node and all its descendants is xdt:untyped, and attributes of the constructed element have type xdt:untypedAtomic.

context item

The context item is the item currently being processed. An item is either an atomic value or a node.

context node

When the context item is a node, it can also be referred to as the context node.

context position

The context position is the position of the context item within the sequence of items currently being processed.

context size

The context size is the number of items in the sequence of items currently being processed.

current date and time

Current date and time. This information represents an implementation-dependent point in time during processing of a query or transformation. It can be retrieved by the fn:current-date, fn:current-time, and fn:current-dateTime functions. If invoked multiple times during the execution of a query or transformation, these functions always return the same result.

data model

XQuery operates on the abstract, logical structure of an XML document, rather than its surface syntax. This logical structure is known as the data model, which is defined in the [XQuery 1.0 and XPath 2.0 Data Model] document.

data model schema

For a given node in the data model, the data model schema is defined as the schema from which the type annotation of that node was derived.

default collation

Default collation. This identifies one of the collations in statically known collations as the collation to be used by string comparison functions and operators when no explicit collation is specified.

default element/type namespace

Default element/type namespace. This is a namespace URI or "none". The namespace URI, if present, is used for any unprefixed QName appearing in a position where an element or type name is expected.

default function namespace

Default function namespace. This is a namespace URI that is used for any unprefixed QName appearing as the function name in a function call. The initial default function namespace may be provided by the external environmentor by a declaration in a Prolog.

default ordering declaration

A default ordering declaration sets the ordering mode in the static context.

Delimiting Terminal

A delimiting terminal may delimit adjacent non-delimiting terminals. Delimiting terminals are only recognized in the appropriate lexical states as specificed by A.2.4 Lexical Rules.

direct element constructor

A direct element constructor is a form of element constructor in which the name of the constructed element is a constant.

document order

Informally, document order is the order defined by a pre-order, depth-first traversal of the nodes in the data model.

dynamic context

The dynamic context of an expression is defined as information that is available at the time the expression is evaluated.

dynamic error

A dynamic error is an error that must be detected during the evaluation phase and may be detected during the analysis phase. Numeric overflow is an example of a dynamic error.

dynamic evaluation phase

The dynamic evaluation phase occurs after completion of the static analysis phase. During the dynamic evaluation phase, the value of the query is computed.

dynamic type

A dynamic type is associated with each value as it is computed. The dynamic type of a value may be either a structural description (such as "sequence of integers") or a named type.

effective boolean value

The effective boolean value of a value is defined as the result of applying the fn:boolean function to the value, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].

empty sequence

A sequence containing zero items is called an empty sequence.

error value

A dynamic error carries an error value, which may be a single item or an empty sequence.

expanded QName

An expanded QName consists of an optional namespace URI and a local name.

expression context

The expression context for a given expression consists of all the information that can affect the result of the expression.

external function

External functions are functions that are implemented outside the query environment.

focus

The first three components of the dynamic context (context item, context position, and context size) are called the focus of the expression.

Full Axis Feature

An XQuery implementation that supports the Full Axis Feature must support all the optional axes.

functional langauge

XQuery is a functional language, which means that expressions can be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitutability if the variable declaration contains construction of new nodes.)

function implementation

Function implementations. Each function in function signatures has a function implementation that enables the function to map instances of its parameter types into an instance of its result type. For a user-defined function, the function implementation is an XQuery expression. For an external function, the function implementation is implementation-dependent.

function signature

Function signatures. This component defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its expanded QName and its arity (number of parameters).

Ignorable whitespace

Unless otherwise specified (see A.2.2.2 ExplicitSpecial Whitespace Handling), Ignorable whitespace may occur between terminals, and is not significant to the parse tree. For readability, whitespace may be used in most expressions even though not explicitly notated in the EBNF. All allowable whitespace that is not explicitly specified in the EBNF is ignorable whitespace, and converse, this term does not apply to whitespace that is explicitly specified.

implementation defined

Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementor for each particular implementation.

implementation dependent

Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementor for any particular implementation.

implicit timezone

Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or in any other operation. This value is an instance of xdt:dayTimeDuration that is implementation-defined . See [ISO 8601] for the range of legal values of a timezone.

initializing expression

If a variable declaration includes an expression, the expression is called an initializing expression.

in-scope attribute declarations

In-scope attribute declarations. Each attribute declaration is identified either by an expanded QName (for a top-level attribute declaration) or by an implementation-dependent attribute identifier (for a local attribute declaration). If the Schema Import Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.

in-scope element declarations

In-scope element declarations. Each element declaration is identified either by an expanded QName (for a top-level element declaration) or by an implementation-dependent element identifier (for a local element declaration). If the Schema Import Feature is supported, in-scope element declarations include all element declarations found in imported schemas.

in-scope namespaces

The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI, thus defining the set of namespace prefixes that are available for interpreting QNames within the scope of the element. For a given element, one namespace binding may have an empty prefix; the URI of this namespace binding is the default namespace within the scope of the element.

in-scope schema definitions

In-scope schema definitions. This is a generic term for all the element, attribute, and type definitions that are in scope during processing of an expression.

in-scope type definitions

In-scope type definitions. Each named type definition is identified either by an expanded QName (for a named type) or by an implementation-dependent type identifier (for an anonymous type). The in-scope type definitions include the predefined types described in 2.4.1 Predefined Types. If the Schema Import Feature is supported, in-scope type definitions also include all type definitions found in imported schemas.

in-scope variables

In-scope variables. This is a set of (expanded QName, type) pairs. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.

item

An item is either an atomic value or a node.

kind test

An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.

lexical action

A lexical action is an action that occurs as an side-effect of a pattern recognition.

lexical state

A lexical state is a condition where a defined set of patterns are recognized.

library module

A module that does not contain a Query Body is called a library module.

literal

A literal is a direct syntactic representation of an atomic value.

local namespace declaration

A local namespace declaration in a computed element constructor contains an optional namespace prefix and a namespace URI expressed as a string literal.

main module

A main module consists of single module resource containing a Prolog followed by a Query Body.

module

A query can be assembled from one or more fragments called modules. Each module is either a main module or a library module.

module declaration

A module declaration serves to identify a module resource as part of a library module. A module declaration consists of the keyword module followed by a namespace prefix and a string literal which must contain a valid URI. [err:XQ0046]

module import

A module import imports the function declarations and variable declarations from a library module into the function signatures and in-scope variables of the importing module resource.

module resource

Each module resource is a fragment of XQuery code that conforms to the Module grammar and can independently undergo the static analysis phase described in 2.2.3 Expression Processing.

must understand

An implementation may extend XQuery functionality by supporting must-understand extensions. A must-understand extension may be used anywhere that ignorable whitespace is allowed.

namespace declaration

A namespace declaration declares a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of statically known namespaces.

namespace declaration attribute

A namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix or to set the default element/type namespace for the constructed element node, including its attributes.

name test

A node test that consists only of a QName or a Wildcard is called a name test.

node

A node is an instance of one of the node kinds defined in [XQuery 1.0 and XPath 2.0 Data Model].

node test

A node test is a condition that must be true for each node selected by a step.

Non-delimiting Terminal

Non-delimiting terminals generally start and end with alphabetic characters or digits. Adjacent non-delimiting terminals must be delimited by a delimiting terminal. Non-delimiting terminals are only recognized in the appropriate lexical states as specificed by A.2.4 Lexical Rules.

optional axis

The following axes are designated as optional axes: ancestor, ancestor-or-self, following, following-sibling, preceding, and preceding-sibling.

ordering mode

Ordering mode. Ordering mode, which has the value ordered or unordered, affects the ordering of the result sequence returned by path expressions, union, intersect, and except expressions, and FLWOR expressions that have no order by clause.

pragma

A pragma may be used to provide additional information to an XQuery implementation.

primary expression

Primary expressions are the basic primitives of the language. They include literals, variable references, context item expressions, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.

principal node kind

Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain.

production

A production combines symbols to form more complex patterns.

Prolog

A Prolog is a series of declarations and imports that define the processing environment for the module resource that contains the Prolog.

QName

Lexically, a QName consists of an optional namespace prefix and a local name.

query body

The Query Body, if present, consists of an expression that defines the result of the query.

reverse document order

The node ordering that is the reverse of document order is called reverse document order.

schema import

A schema import imports the element, attribute, and type definitions from a schema into the in-scope schema definitions.

Schema Import Feature

If the Schema Import Feature is supported, a Prolog may contain a schema import. Definitions from the imported schema are added to the in-scope schema definitions.

sequence

A sequence is an ordered collection of zero or more items.

SequenceType

When it is necessary to refer to a type in an XQuery expression, the SequenceType syntax is used. The name SequenceType suggests that this syntax is used to describe the type of an XQuery value, which is always a sequence.

SequenceType matching

During evaluation of an expression, it is sometimes necessary to determine whether a value with a known type "matches" an expected type, expressed in the SequenceType syntax. This process is known as SequenceType matching.

serialization

Serialization is the process of converting a sequence of nodes and atomic values from the data model into a sequence of octets (step DM4 in Figure 1.)

setter

Certain declarations in a Prolog are called setters because they set the value of some property that influences query processing, such as construction mode, ordering mode, or default collation.

singleton sequence

A sequence containing exactly one item is called a singleton sequence.

statically known collations

Statically known collations. This is a set of (URI, collation) pairs. It defines the names of the collations that are available for use in function calls that take a collation name as an argument.

statically known collections

Statically known collections. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:collection function. The type is the type of the sequence of nodes that would result from calling the fn:collection function with this URI as its argument.

statically known documents

Statically known documents. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:doc function. The type is the static type of a call to fn:doc with the given URI as its literal argument.

statically known namespaces

Statically known namespaces. This is a set of (prefix, URI) pairs that define all the namespaces that are known during static processing of a given expression.

static analysis phase

The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).

static context

The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.

static error

A static error is an error that must be detected during the analysis phase. A syntax error is an example of a static error. The means by which static errors are reported during the analysis phase is implementation-defined.

static type

The static type of an expression may be either a named type or a structural description—for example, xs:boolean? denotes an optional occurrence of the xs:boolean type. The rules for inferring the static types of various expressions are described in [XQuery 1.0 and XPath 2.0 Formal Semantics].

static typing extension

A static typing extension is a type inference rule that infers a more precise static type than that inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics].

Static Typing Feature

An XQuery implementation that does not support the Static Typing Feature is not required to raise type errors during the static analysis phase.

strongly typed

XQuery is also a strongly-typed language in which the operands of various expressions, operators, and functions must conform to the expected types.

substitution group

Substitution groups are defined in [XML Schema] Part 1, Section 2.2.2.2. Informally, the substitution group headed by a given element (called the head element) consists of the set of elements that can be substituted for the head element without affecting the outcome of schema validation.

subtype substitution

The use of a value whose actual type is derived from the expected type is known as subtype substitution.

symbol

Each rule in the grammar defines one symbol, in the form

target namespace

Each imported schema or module is identified by its target namespace, which is the namespace of the objects (such as elements or functions) that are defined by the schema or module.

terminal

A terminal is a single unit of the grammar that can not be further subdivided, and is specified in the EBNF by a character or characters in quotes, or a regular expression.

type error

A type error may be raised during the analysis or evaluation phase. During the analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs.

type promotion

Under certain circumstances, an atomic value can be promoted from one type to another. Type promotion is used in function calls (see 3.1.5 Function Calls) and in processing of operators that accept numeric operands (see B.2 Operator Mapping).

user-defined function

For a user-defined function, the function declaration includes an expression called the function body that defines how the result of the function is computed from its parameters.

variable values

Variable values. This is a set of (expanded QName, value) pairs. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The QName is the name of the variable and the value is the dynamic value of the variable.

version declaration

Any module resource may contain a version declaration. If present, the version declaration occurs at the beginning of the module resource and identifies the applicable XQuery syntax and semantics for the module resource.

Whitespace

Whitespace characters are defined by [http://www.w3.org/TR/REC-xml#NT-S] when these characters occur outside of a StringLiteral.

xdt:anyAtomicType

xdt:anyAtomicType includes all atomic values (and no values that are not atomic).

xdt:dayTimeDuration

xdt:dayTimeDuration is a subtype of xs:duration whose lexical representation is restricted to contain only day, hour, minute, and second components.

xdt:untyped

xdt:untyped is used to denote the dynamic type of an element node that has not been validated, or has been validated in skip mode.

xdt:untypedAtomic

xdt:untypedAtomic is used to denote untyped atomic data, such as text that has not been assigned a more specific type.

xdt:yearMonthDuration

xdt:yearMonthDuration is a subtype of xs:duration whose lexical representation is restricted to contain only year and month components.

xmlspace declaration

The xmlspace declaration in a Prolog controls whether boundary whitespace is preserved by direct element constructors during execution of the query.

XML space policy

XMLSpace policy. This policy, declared in the Prolog, controls the processing of whitespace by element constructors.

XPath 1.0 compatibility mode

XPath 1.0 compatibility mode. This component must be set by all host languages that include XPath 2.0 as a subset, indicating whether rules for compatibility with XPath 1.0 are in effect. XQuery sets the value of this component to false.

XQuery Flagger

An XQuery Flagger is a facility that is provided by an implementation that is able to identify queries that contain must-understand extensions. If an implementation supports must-understand extensions, then an XQuery Flagger must be provided.

XQuery static flagger

An XQuery Static Flagger is a facility that is able to identify queries that require a static typing extension.

F Summary of Error Conditions (Non-Normative)

err:XP0001

It is a static error if analysis of an expression relies on some component of the static context that has not been assigned a value.

err:XP0002

It is a dynamic error if evaluation of an expression relies on some part of the dynamic context that has not been assigned a value.

err:XP0003

It is a static error if an expression is not a valid instance of the grammar defined in A.1 EBNF.

err:XP0004

During the analysis phase, it is a type error if the static typing feature is in effect and an expression is found to have a static type that is not appropriate for the context in which the expression occurs.

err:XP0005

During the analysis phase, it is a static error if the static typing feature is in effect and the static type assigned to an expression other than the expression () or data(()) is the empty type.

err:XP0006

During the evaluation phase, it is a type error if a value does not match a required type as specified by the matching rules in 2.4.4 SequenceType Matching.

err:XP0007

It is a type error if the fn:data function is applied to a node whose type annotation denotes a complex type with non-mixed complex content.

err:XP0008

It is a static error if an expression refers to an element name, attribute name, type name, function name, namespace prefix, or variable name that is not defined in the static context, except within an ElementTest or an AttributeTest.

err:XQ0009

An implementation that does not support the Schema Import Feature may raise a static error if a prolog contains a schema import.

err:XQ0010

An implementation that does not support the Full Axis Feature must raise a static error if it encounters a reference to an optional axis that it does not support.

err:XQ0012

If the Schema Import Feature is in effect, it is a static error if the set of definitions contained in all imported schemas do not satisfy the conditions for schema validity specified in Sections 3 and 5 of [XML Schema] Part 1. In particular, the definitions must be valid, they must be complete, and they must be unique -- that is, the pool of definitions must not contain two or more schema components with the same name and target namespace.

err:XQ0013

It is a static error if an implementation supports a pragma but determines that its content is invalid.

err:XQ0014

It is a static error if an implementation does not support a must-understand extension or an implementation does support a must-understand extension and the implementation determines that the character content is invalid.

err:XQ0015

It is a static error if the XQuery Flagger is enabled and the query contains a must-understand extension.

err:XQ0016

An implementation that does not support the Module Feature raises a static error if it encounters a module declaration or a module import.

err:XP0017

It is a static error if the expanded QName and number of arguments in a function call do not match the name and arity of a function signature in the static context.

err:XP0018

It is a static error for an expression to depend on the focus when the focus is undefined.

err:XP0019

It is a type error if the result of a step expression (StepExpr) is not a (possibly empty) sequence of nodes.

err:XP0020

It is a type error if in an axis expression, the context item is not a node.

err:XP0021

It is a dynamic error if the argument of a cast expression or constructor function cannot be cast to the required type.

err:XQ0022

It is a static error if the value of a namespace declaration attribute is not a literal string.

err:XQ0023

(Not currently used.)

err:XQ0024

It is a type error if the content sequence in an element constructor contains an attribute node following a node that is not an attribute node.

err:XQ0025

It is a dynamic error if any attribute of a constructed element does not have a name that is distinct from the names of all other attributes of the constructed element.

err:XQ0026

It is a dynamic error if the result of either the name expression or the content expression of a computed processing instruction constructor contains the string "?>".

err:XQ0027

In a validate expression, it is a dynamic error if validation fails.

err:XQ0028

(Not currently used.)

err:XP0029

It is a dynamic error in a cast expression if the input value does not satisfy the facets of the target type.

err:XQ0030

It is a type error if the argument of a validate expression does not evaluate to exactly one document or element node.

err:XQ0031

It is a static error if the version number specified in a version declaration is not supported by the implementation.

err:XQ0032

A static error is raised if a prolog contains multiple declarations for the base URI.

err:XQ0033

It is a static error if a prolog contains multiple declarations for the same namespace prefix.

err:XQ0034

It is a static error if multiple functions declared or imported by a module resource have the same expanded QName and the same number of arguments.

err:XQ0035

It is a static error to import two schema components that both define the same name in the same symbol space and in the same scope.

err:XQ0036

It is a type error to import a module if the importing module's in-scope type definitions do not include definitions for the type names that appear in variable declarations, function parameters, or function returns found in the imported module.

err:XQ0037

It is a static error to import a module that contains function declarations or variable declarations whose names are already declared in the static context of the importing module.

err:XQ0038

It is a static error if a prolog specifies more than one default collation, or value specified does not identify a collation known to the implementation.

err:XQ0039

It is an static error for a function declaration to have more than one parameter with the same name.

err:XQ0040

It is an static error if the attributes specified by a direct element constructor do not have distinct names.

err:XQ0041

It is a dynamic error if the value of the name expression in a computed processing instruction constructor cannot be cast to the type xs:NCName.

err:XQ0042

It is a static error if a computed element constructor contains more than one content expression, or if it contains a local namespace declaration following a content expression.

err:XQ0043

It is a static error if two or more local namespace declarations within the same computed element constructor have same namespace prefix or have no namespace prefix.

err:XQ0044

It is a dynamic error if the name expression of a computed attribute constructor returns a QName that is in the namespace http://www.w3.org/TR/REC-xml-names (corresponding to namespace prefix xmlns), or returns a QName that is in no namespace and has local name xmlns.

err:XQ0045

It is a static error if the function name in a function declaration is in one of the following namespaces: http://www.w3.org/XML/1998/namespace, http://www.w3.org/2001/XMLSchema, http://www.w3.org/2001/XMLSchema-instance, http://www.w3.org/2004/07/xpath-functions, http://www.w3.org/2004/07/xpath-datatypes.

err:XQ0046

It is a static error if a string that is required to contain a valid URI does not contain a valid lexical form according to the definition of xs:anyURI in [XML Schema].

err:XQ0047

It is a static error if multiple module imports in the same Prolog specify the same target namespace.

err:XQ0048

It is a static error if a function or variable declared in a library module is not in the target namespace of the library module.

err:XQ0049

It is a static error if more than one variable declared or imported by a module resource has the same expanded QName.

err:XP0050

It is a dynamic error if the dynamic type of the operand of a treat expression does not match the type specified by the treat expression.

err:XP0051

It is a static error if a QName that is used as an AtomicType in a SequenceType is not defined in the in-scope type definitions as an atomic type.

err:XQ0052

It is a dynamic error if the content of a node constructor includes an atomic value that cannot be cast into a string, such as a value of type xs:QName or xs:NOTATION.

err:XQ0053

It is a static error if the string literal used in a namespace declaration to specify a URI is a zero-length string, and the implementation does not support [XML Names 1.1].

err:XQ0054

It is a static error if the initializing expression in a variable declaration cannot be executed because of a circularity (for example, the expression depends on a function that in turn depends on the value of the initialized variable).

err:XP0055

(Not currently used.)

err:XQ0056

It is a static error if the target namespace specified in a module import is the same as the target namespace of the importing module.

err:XQ0057

It is a static error if a schema import binds a namespace prefix but does not specify a target namespace other than a zero-length string.

err:XQ0058

It is a static error if multiple schema imports specify the same target namespace.

err:XQ0059

It is a static error if an implementation is unable to process a schema or module import by finding a schema or module with the specified target namespace.

err:XQ0060

It is a static error if the name of a function in a function declaration is not in a namespace (expanded QName has an empty URI).

err:XQ0061

It is a dynamic error if validity assessment is performed on a document node unless the children of the document node comprise exactly one element node, no text nodes, and zero or more comment and processing instruction nodes, in any order.

err:XQ0062

It is a dynamic error if a document-level constraint is not satisfied when validity assessment is performed on a document node. Document-level constraints include identity constraints (xs:unique, xs:key, and xs:keyref) and ID/IDREF constraints.

err:XQ0063

It is a static error if the URI specified by a default function namespace declaration is a zero-length string.

err:XQ0064

It is a dynamic error if the value of the name expression in a computed processing instruction constructor is equal to "XML" (in any combination of upper and lower case).

err:XQ0065

A static error is raised if a prolog contains multiple default ordering declarations.

err:XQ0066

A static error is raised if a prolog contains more than one default element/type namespace declaration, or more than one default function namespace declaration.

err:XQ0067

A static error is raised if a prolog contains multiple construction declarations.

G Example Applications (Non-Normative)

This section contains examples of several important classes of queries that can be expressed using XQuery. The applications described here include joins across multiple data sources, grouping and aggregation, queries based on sequential relationships, recursive transformations, and selection of distinct combinations of values.

G.1 Joins

Joins, which combine data from multiple sources into a single result, are a very important type of query. In this section we will illustrate how several types of joins can be expressed in XQuery. We will base our examples on the following three documents:

  1. A document named parts.xml that contains many part elements; each part element in turn contains partno and description subelements.

  2. A document named suppliers.xml that contains many supplier elements; each supplier element in turn contains suppno and suppname subelements.

  3. A document named catalog.xml that contains information about the relationships between suppliers and parts. The catalog document contains many item elements, each of which in turn contains partno, suppno, and price subelements.

A conventional ("inner") join returns information from two or more related sources, as illustrated by the following example, which combines information from three documents. The example generates a "descriptive catalog" derived from the catalog document, but containing part descriptions instead of part numbers and supplier names instead of supplier numbers. The new catalog is ordered alphabetically by part description and secondarily by supplier name.

<descriptive-catalog>
   { 
     for $i in fn:doc("catalog.xml")//item,
         $p in fn:doc("parts.xml")//part[partno = $i/partno],
         $s in fn:doc("suppliers.xml")//supplier[suppno = $i/suppno]
     order by $p/description, $s/suppname
     return
        <item>
           {
           $p/description,
           $s/suppname,
           $i/price
           }
        </item>
   }
</descriptive-catalog>

The previous query returns information only about parts that have suppliers and suppliers that have parts. An outer join is a join that preserves information from one or more of the participating sources, including elements that have no matching element in the other source. For example, a left outer join between suppliers and parts might return information about suppliers that have no matching parts.

The following query demonstrates a left outer join. It returns names of all the suppliers in alphabetic order, including those that supply no parts. In the result, each supplier element contains the descriptions of all the parts it supplies, in alphabetic order.

for $s in fn:doc("suppliers.xml")//supplier
order by $s/suppname
return
   <supplier>
      { 
        $s/suppname,
        for $i in fn:doc("catalog.xml")//item
                 [suppno = $s/suppno],
            $p in fn:doc("parts.xml")//part
                 [partno = $i/pno]
        order by $p/description
        return $p/description 
      }
   </supplier>

The previous query preserves information about suppliers that supply no parts. Another type of join, called a full outer join, might be used to preserve information about both suppliers that supply no parts and parts that have no supplier. The result of a full outer join can be structured in any of several ways. The following query generates a list of supplier elements, each containing nested part elements for the parts that it supplies (if any), followed by a list of part elements for the parts that have no supplier. This might be thought of as a "supplier-centered" full outer join. Other forms of outer join queries are also possible.

<master-list>
 {
    for $s in fn:doc("suppliers.xml")//supplier
    order by $s/suppname
    return
        <supplier>
           { 
             $s/suppname,
             for $i in fn:doc("catalog.xml")//item
                     [suppno = $s/suppno],
                 $p in fn:doc("parts.xml")//part
                     [partno = $i/partno]
             order by $p/description
             return
                <part>
                   {
                     $p/description,
                     $i/price
                   }
                </part> 
           }
        </supplier> 
    ,
    (: parts that have no supplier :)
    <orphan-parts>
       { for $p in fn:doc("parts.xml")//part
         where fn:empty(fn:doc("catalog.xml")//item
               [partno = $p/partno] )
         order by $p/description
         return $p/description 
       }
    </orphan-parts>
 }
</master-list>

The previous query uses an element constructor to enclose its output inside a master-list element. The concatenation operator (",") is used to combine the two main parts of the query. The result is an ordered sequence of supplier elements followed by an orphan-parts element that contains descriptions of all the parts that have no supplier.

G.2 Grouping

Many queries involve forming data into groups and applying some aggregation function such as fn:count or fn:avg to each group. The following example shows how such a query might be expressed in XQuery, using the catalog document defined in the previous section.

This query finds the part number and average price for parts that have at least 3 suppliers.

for $pn in fn:distinct-values(fn:doc("catalog.xml")//partno)
let $i := fn:doc("catalog.xml")//item[partno = $pn]
where fn:count($i) >= 3
order by $pn
return 
   <well-supplied-item>
      <partno> {$p} </partno>
      <avgprice> {fn:avg($i/price)} </avgprice>
   </well-supplied-item>

The fn:distinct-values function in this query eliminates duplicate part numbers from the set of all part numbers in the catalog document. The result of fn:distinct-values is a sequence in which order is not significant.

Note that $pn, bound by a for clause, represents an individual part number, whereas $i, bound by a let clause, represents a set of items which serves as argument to the aggregate functions fn:count($i) and fn:avg($i/price). The query uses an element constructor to enclose each part number and average price in a containing element called well-supplied-item.

The method illustrated above generalizes easily to grouping by more than one data value. For example, consider a census document containing a sequence of person elements, each with subelements named state, job, and income. A census analyst might need to prepare a report listing the average income for each combination of state and job. This report might be produced using the following query:

for $s in fn:distinct-values(fn:doc("census.xml")//state),
    $j in fn:distinct-values(fn:doc("census.xml")//job)
let $p := fn:doc("census.xml")//person[state = $s and job = $j]
order by $s, $j
return 
   if (fn:exists($p)) then
      <group>
         <state> {$s} </state>
         <job> {$j} </job>
         <avgincome> {fn:avg($p/income)} </avgincome>
      </group>
   else ()

The if-then-else expression in the above example prevents generation of groups that contain no data. For example, the census data may contain some persons who live in Nebraska, and some persons whose job is Deep Sea Fisherman, but no persons who live in Nebraska and have the job of Deep Sea Fisherman. If output groups are desired for all possible combinations of states and jobs, the if-then-else expression can be omitted from the query. In this case, the output may include "empty" groups such as the following:

<group>
   <state>Nebraska</state>
   <job>Deep Sea Fisherman</state>
   <avgincome/>
</group>

G.3 Queries on Sequence

XQuery uses the << and >> operators to compare nodes based on document order. Although these operators are quite simple, they can be used to express complex queries for XML documents in which sequence is meaningful. The first two queries in this section involve a surgical report that contains procedure, incision, instrument, action, and anesthesia elements.

The following query returns all the action elements that occur between the first and second incision elements inside the first procedure. The original document order among these nodes is preserved in the result of the query.

let $proc := //procedure[1]
for $i in $proc//action
where $i >> ($proc//incision)[1]
   and $i << ($proc//incision)[2]
return $i

It is worth noting here that document order is defined in such a way that a node is considered to precede its descendants in document order. In the surgical report, an action is never part of an incision, but an instrument is. Since the >> operator is based on document order, the predicate $i >> ($proc//incision)[1] is true for any instrument element that is a descendant of the first incision element in the first procedure.

For some queries, it may be helpful to define a function that can test whether a node precedes another node without being its ancestor. The following function returns true if its first operand precedes its second operand but is not an ancestor of its second operand; otherwise it returns false:

declare function local:precedes($a as node(), $b as node()) 
   as boolean
   {
      $a << $b
        and
      fn:empty($a//node() intersect $b) 
   };

Similarly, a local:follows function could be written:

declare function local:follows($a as node(), $b as node()) 
   as boolean
   {
      $a >> $b
        and
      fn:empty($b//node() intersect $a) 
   };

Using the local:precedes function, we can write a query that finds instrument elements between the first two incisions, excluding from the query result any instrument that is a descendant of the first incision:

let $proc := //procedure[1]
for $i in $proc//instrument
where local:precedes(($proc//incision)[1], $i)
   and local:precedes($i, ($proc//incision)[2])
return $i

The following query reports incisions for which no prior anesthesia was recorded in the surgical report. Since an anesthesia is never part of an incision, we can use << instead of the less-efficient local:precedes function:

for $proc in //procedure
where some $i in $proc//incision satisfies
         fn:empty($proc//anesthesia[. << $i])
return $proc

In some documents, particular sequences of elements may indicate a logical hierarchy. This is most commonly true of HTML. The following query returns the introduction of an XHTML document, wrapping it in a div element. In this example, we assume that an h2 element containing the text "Introduction" marks the beginning of the introduction, and the introduction continues until the next h2 or h1 element, or the end of the document, whichever comes first.

let $intro := //h2[text()="Introduction"],
    $next-h := //(h1|h2)[. >> $intro][1]
return
   <div>
     {
       $intro,
       if (fn:empty($next-h))
         then //node()[. >> $intro]
         else //node()[. >> $intro and . << $next-h]
     }
   </div>

Note that the above query makes explicit the hierarchy that was implicit in the original document. In this example, we assume that the h2 element containing the text "Introduction" has no subelements.

G.4 Recursive Transformations

Occasionally it is necessary to scan over a hierarchy of elements, applying some transformation at each level of the hierarchy. In XQuery this can be accomplished by defining a recursive function. In this section we will present two examples of such recursive functions.

Suppose that we need to compute a table of contents for a given document by scanning over the document, retaining only elements named section or title, and preserving the hierarchical relationships among these elements. For each section, we retain subelements named section or title; but for each title, we retain the full content of the element. This might be accomplished by the following recursive function:

declare function local:sections-and-titles($n as node()) as node()?
   {
   if (fn:local-name($n) = "section")
   then element
          { fn:local-name($n) }
          { for $c in $n/* return local:sections-and-titles($c) }
   else if (fn:local-name($n) = "title")
   then $n
   else ( )
   };

The "skeleton" of a given document, containing only its sections and titles, can then be obtained by invoking the local:sections-and-titles function on the root node of the document, as follows:

local:sections-and-titles(fn:doc("cookbook.xml"))

As another example of a recursive transformation, suppose that we wish to scan over a document, transforming every attribute named color to an element named color, and every element named size to an attribute named size. This can be accomplished by the following recursive function:

declare function local:swizzle($n as node()) as node() 
  { 
   typeswitch($n)
     case $a as attribute(color)
       return element color { fn:string($a) } 
     case $es as element(size) 
       return attribute size { fn:string($es) } 
     case $e as element() 
       return element 
         { fn:local-name($e) } 
         { for $c in $e/(* | @*) return local:swizzle($c) } 
     case $d as document-node() 
       return document 
         { for $c in $d/* return local:swizzle($c) } 
     default return $n 
  };

The transformation can be applied to a whole document by invoking the local:swizzle function on the root node of the document, as follows:

local:swizzle(fn:doc("plans.xml"))

G.5 Selecting Distinct Combinations

It is sometimes necessary to search through a set of data to find all the distinct combinations of a given list of properties. For example, an input data set might consist of a large set of order elements, each of which has the same basic structure, as illustrated by the following example:

<order>
   <date>2003-10-15</date>
   <product>Dress Shirt</product>
   <size>M</size>
   <color>Blue</color>
   <supplier>Fashion Trends</supplier>
   <quantity>50</quantity>
</order>

From this data set, a user might wish to find all the distinct combinations of product, size, and color that occur together in an order. The following query returns this list, enclosing each distinct combination in a new element named option:

for $p in fn:distinct-values(//product),
    $s in fn:distinct-values(//size),
    $c in fn:distinct-values(//color)
    order by $p, $s, $c
    return
       if (fn:exists(//order[product eq $p
                and size eq $s and color eq $c]))
       then
          <option>
             <product>{$p}</product>
             <size>{$s}</size>
             <color>{$c}</color>
          </option>
       else ()

H XPath 2.0 and XQuery 1.0 Issues (Non-Normative)

The XPath 2.0 and XQuery 1.0 Issues List that records pre-Last Call issues can be found at http://www.w3.org/XML/2003/11/xpath-xquery-issues.

I Revision Log (Non-Normative)

This log records the changes that have been made to this document since the Last Call Draft of 12 November 2003.

I.1 23 July 2004

  1. An ordering declaration has been added to the Prolog, which affects the ordering semantics of path expressions, FLWOR expressions, and union, intersect, and except expressions. In addition, ordered and unordered operators have been introduced that permit ordering semantics to be controlled at the expression level within a query.

  2. The SequenceType syntax has been simplified. SchemaContextPath is no longer part of the SequenceType syntax. Also, the section on SequenceType Matching has been rewritten to make its terminology more consistent with the Formal Semantics document.

  3. Validation has been separated from construction. Validation now occurs only as a result of an explicit validate expression. Validation modes are strict and lax, and are specified on the validate expression. New construction modes strip and preserve have been defined and are declared in the Prolog. The notion of "validation context" has been deleted. The XQuery definition of validation has been converged with the definition used in XSLT.

  4. It is now permitted for multiple user-defined functions to have the same name as long as they have different numbers of arguments.

  5. The term xdt:untypedAny is changed to xdt:untyped.

  6. xs:anyType is no longer an abstract type, but is now used to denote the type of a partially validated element node. Since there is no longer a meaningful distinction between abstract types and concrete types, these terms are no longer used in this document.

  7. Value comparisons now return () if either operand is ().

  8. Computed namespace constructors are now completely static and are allowed only inside a computed element constructor. Namespace declarations in a computed element constructor must come before the element content, and must consist entirely of literals. The namespace prefix is optional. If absent, it has the effect of setting the default namespace for elements and types within the scope of the constructed element.

  9. The name of the Predicates grammar production has been changed to PredicateList.

  10. Grammar changes have been made in the Prolog, including constraints on the order of declarations and imports.

  11. The grammar production formerly called a FilterStep is now called a FilterExpression and is described in a separate section rather than as part of a path expression.

  12. The precedence of the cast and treat operators in the grammar has been increased.

  13. The precedence of unary arithmetic operators has been increased.

  14. The syntax for variable initialization in the Prolog now uses an assignment operator (":="). Also, circularities in variable initialization are now considered to be a static errors.

  15. The appendix containing a list of error messages has been made non-normative.

  16. An error is raised if a module attempts to import itself (target namespace of importing module and imported modules are the same).

  17. A schema can now be imported without specifying either a target namespace or a location hint.

  18. Module imports and schema imports now accept multiple location hints, representing multiple physical resources in the same module or schema.

  19. CData Sections are no longer considered to be constructors, but are simply a notational convenience for embedding special characters in the content of an element or attribute constructor.

  20. Three new components have been added to the static context: XQuery Flagger status, XQuery Static Flagger status, and context item static type.

  21. The expression data(()) no longer raises a static error, although its static type is empty.

  22. If a dynamic implementation detects a static error, the evaluation phase is optional.

  23. XPath allows host languages to specify whether they recognize the concept of a namespace node. XQuery does not recognize namespace nodes. Instead, it recognizes an "in-scope namespaces" property of an element node.

  24. The specification now clearly distinguishes between "statically-known namespaces" (a static property of an expression) and "in-scope namespaces" (a dynamic property of an element).

  25. An order by clause may now accept values of mixed type if they have a common type that is reachable by numeric promotion and/or moving up the type derivation hierarchy, and if this common type has a gt operator.

  26. In element and document node constructors, if the content sequence contains a document node, that node is replaced by its children (this was previously treated as an error).

  27. Atomization now applies to the name expression of a computed processing instruction constructor.

  28. It is now implementation-defined whether undeclaration of namespace prefixes in an element constructor is supported. If supported, this feature conforms to the semantics of Namespaces 1.1. In other words, if an element constructor binds a namespace prefix to the zero-length string, any binding of that prefix defined at an outer level is suspended within the scope of the constructed element.

  29. The names of certain components in the static and dynamic contexts have been changed to make them more consistent and descriptive.

  30. In a computed text node constructor, the expression enclosed in curly braces is no longer optional, since it is not possible to construct an empty text node.

  31. The definition of the idiv operator has been made consistent with the Functions and Operators document. The idiv operator accepts operands of any numeric types, performs a division, and truncates the result to an integer.

  32. Certain grammar productions have been renamed and reordered to make the grammar easier to read.

  33. The section on constructor functions has been edited to make it more consistent with the definition of constructor functions in the Functions and Operators document.

  34. The Comments section has been moved out of the Primary Expressions section, because a comment is not a primary expression.

  35. The term "module resource" has been introduced to represent a fragment of XQuery code that can independently undergo static analysis. A module may comprise several module resources. Each module resource has its own static and dynamic context.

  36. Rules for processing comment constructors have changed, to ensure that the resulting comment does not contain adjacent hyphens or end with a hyphen.

  37. Some additional constraints have been added to the section titled "Consistency Constraints".

  38. Various minor changes, both editorial and substantive, have been made in response to public comments and working group discussions.