Copyright © 2005 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.
This document defines formally the semantics of XQuery 1.0 [XQuery 1.0: A Query Language for XML] XPath 2.0 [XML Path Language (XPath) 2.0].
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.
This version includes all changes made in response to comments received during the Last Call period that ended on Feb. 15, 2004. The corresponding decisions are recorded in the Formal Semantics Last Call issues list (http://www.w3.org/2005/06/formal-semantics-issues.html). A list of changes introduced by this draft can be found in [F Revision Log].
XQuery 1.0, XPath 2.0, and their formal semantics has been defined jointly by the XML Query Working Group and the XSL Working Group (both part of the XML Activity).
This is a Last Call Working Draft. Comments on this document are due no later than 15 July 2005. Comments should be entered into the last-call issue tracking system for this specification (instructions can be found at http://www.w3.org/XML/2005/04/qt-bugzilla). If access to that system is not feasible, you may send your comments to the W3C mailing list public-qt-comments@w3.org. (archived at http://lists.w3.org/Archives/Public/public-qt-comments/) with "[FS]" at the beginning of the subject field.
The patent policy for this document is the 5 February 2004 W3C Patent Policy. 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.
1 Introduction
1.1 Normative and Informative Sections
2 Preliminaries
2.1 Introduction to the Formal Semantics
2.1.1 Notations from grammar productions
2.1.2 Notations for judgments
2.1.3 Notations for inference rules
2.1.4 Notations for environments
2.1.5 Putting it together
2.2 URIs, Namespaces, and Prefixes
2.3 XML Values
2.3.1 Formal values
2.3.2 Examples of values
2.4 The [XPath/XQuery] Type System
2.4.1 XML Schema and the [XPath/XQuery] Type System
2.4.2 Item types
2.4.3 Content models
2.4.4 Top level definitions
2.4.5 Example of a complete Schema
2.5 Functions and operators
3 Basics
3.1 Expression Context
3.1.1 Static Context
3.1.1.1 Resolving QNames to Expanded QNames
3.1.2 Dynamic Context
3.2 Processing Model
3.2.1 Processing model
3.2.2 Normalization judgment
3.2.3 Static typing judgment
3.2.4 Dynamic evaluation judgment
3.3 Error Handling
3.3.1 Kinds of Errors
3.3.2 Identifying and Reporting Errors
3.3.3 Handling Dynamic Errors
3.3.4 Errors and Optimization
3.4 Concepts
3.4.1 Document Order
3.4.2 Atomization
3.4.3 Effective Boolean Value
3.4.4 Input Sources
3.4.5 URI Literals
3.5 Types
3.5.1 Predefined Schema Types
3.5.2 Typed Value and String Value
3.5.3 SequenceType Syntax
3.5.4 SequenceType Matching
3.6 Comments
4 Expressions
4.1 Primary Expressions
4.1.1 Literals
4.1.2 Variable References
4.1.3 Parenthesized Expressions
4.1.4 Context Item Expression
4.1.5 Function Calls
4.2 Path Expressions
4.2.1 Steps
4.2.1.1 Axes
4.2.1.2 Node Tests
4.2.2 Predicates
4.2.3 Unabbreviated Syntax
4.2.4 Abbreviated Syntax
4.3 Sequence Expressions
4.3.1 Constructing Sequences
4.3.2 Filter Expressions
4.3.3 Combining Node Sequences
4.4 Arithmetic Expressions
4.5 Comparison Expressions
4.5.1 Value Comparisons
4.5.2 General Comparisons
4.5.3 Node Comparisons
4.6 Logical Expressions
4.7 Constructors
4.7.1 Direct Element Constructors
4.7.1.1 Attributes
4.7.1.2 Namespace Declaration Attributes
4.7.1.3 Content
4.7.1.4 Whitespace in Element Content
4.7.2 Other Direct Constructors
4.7.3 Computed Constructors
4.7.3.1 Computed Element Constructors
4.7.3.2 Computed Attribute Constructors
4.7.3.3 Document Node Constructors
4.7.3.4 Text Node Constructors
4.7.3.5 Computed Processing Instruction Constructors
4.7.3.6 Computed Comment Constructors
4.7.4 In-scope Namespaces of a Constructed Element
4.8 [For/FLWR] Expressions
4.8.1 FLWOR expressions
4.8.2 For expression
4.8.3 Let Expression
4.8.4 Order By and Return Clauses
4.9 Ordered and Unordered Expressions
4.10 Conditional Expressions
4.11 Quantified Expressions
4.12 Expressions on SequenceTypes
4.12.1 Instance Of
4.12.2 Typeswitch
4.12.3 Cast
4.12.4 Castable
4.12.5 Constructor Functions
4.12.6 Treat
4.13 Validate Expressions
4.13.1 Validating an Element Node
4.13.2 Validating a Document Node
4.14 Extension Expressions
5 Modules and Prologs
5.1 Version Declaration
5.2 Module Declaration
5.3 Boundary-space Declaration
5.4 Default Collation Declaration
5.5 Base URI Declaration
5.6 Construction Declaration
5.7 Ordering Mode Declaration
5.8 Empty Order Declaration
5.9 Copy-Namespaces Declaration
5.10 Schema Import
5.11 Module Import
5.12 Namespace Declaration
5.13 Default Namespace Declaration
5.14 Variable Declaration
5.15 Function Declaration
5.16 Option Declaration
6 Conformance
6.1 Static Typing Feature
6.1.1 Static Typing Extensions
7 Additional Semantics of Functions
7.1 Formal Semantics Functions
7.1.1 The arithmetic operator pseudo-functions: fs:minus, fs:plus, fs:times, fs:idiv, fs:div, and fs:mod
7.1.2 The comparison pseudo-functions: fs:eq, fs:ne, fs:lt, fs:le, fs:gt, and fs:ge
7.1.3 The fs:convert-operand function
7.1.4 The fs:convert-simple-operand function
7.1.5 The fs:distinct-doc-order function
7.1.6 The fs:distinct-doc-order-or-atomic-sequence function
7.1.7 The fs:item-sequence-to-node-sequence function
7.1.8 The fs:item-sequence-to-untypedAtomic function
7.1.9 The fs:item-sequence-to-untypedAtomic-PI function
7.1.10 The fs:item-sequence-to-untypedAtomic-text function
7.1.11 The fs:item-sequence-to-untypedAtomic-comment function
7.1.12 The fs:apply-ordering-mode function
7.1.13 The fs:to function
7.2 Standard functions with specific typing rules
7.2.1 The fn:last context function
7.2.2 The fn:position context function
7.2.3 The fn:abs, fn:ceiling, fn:floor, fn:round, and fn:round-half-to-even functions
7.2.4 The fn:boolean function
7.2.5 The fn:collection and fn:doc functions
7.2.6 The fn:data function
7.2.7 The fn:distinct-values function
7.2.8 The fn:unordered function
7.2.9 The fn:error function
7.2.10 The fn:min, fn:max, fn:avg, and fn:sum functions
7.2.11 The fn:remove function
7.2.12 The fn:reverse function
7.2.13 The fn:subsequence function
7.2.14 The op:union, op:intersect, and op:except operators
7.2.15 The fn:insert-before function
7.2.16 The fn:zero-or-one, fn:one-or-more, and fn:exactly-one functions
8 Auxiliary Judgments
8.1 Judgments for accessing types
8.1.1 Derives from
8.1.2 Substitutes for
8.1.3 Element and attribute name lookup (Dynamic)
8.1.4 Element and attribute type lookup (Static)
8.1.5 Extension
8.1.6 Mixed content
8.1.7 Type adjustment
8.1.8 Builtin attributes
8.1.9 Type expansion
8.1.10 Union interpretation of derived types
8.2 Judgments for step expressions and filtering
8.2.1 Principal Node Kind
8.2.2 Auxiliary judgments for axes
8.2.2.1 Static semantics of axes
8.2.2.1.1 Inference rules for all axis
8.2.2.1.2 Inference rules for the self axis
8.2.2.1.3 Inference rules for the child axis
8.2.2.1.4 Inference rules for the attribute axis
8.2.2.1.5 Inference rules for the parent axis
8.2.2.1.6 Inference rules for the namespace axis
8.2.2.1.7 Inference rules for the descendant axis
8.2.2.1.8 Inference rules for the descendant-or-self axis
8.2.2.1.9 Inference rules for the ancestor axis
8.2.2.1.10 Inference rules for the ancestor-or-self axis
8.2.2.2 Dynamic semantics of axes
8.2.3 Auxiliary judgments for node tests
8.2.3.1 Static semantics of node tests
8.2.3.1.1 Name Tests
8.2.3.1.2 Kind Tests
8.2.3.2 Dynamic semantics of node tests
8.2.3.2.1 Name Tests
8.2.3.2.2 Kind Tests
8.3 Judgments for type matching
8.3.1 Matches
8.3.2 Subtype and Type equality
8.4 Judgments for FLWOR and other expressions on sequences
8.5 Judgments for function calls
8.5.1 Type promotion
8.6 Judgments for validation modes and contexts
8.6.1 Elements in validation mode
A Normalized core grammar
A.1 Core BNF
B Functions and Operators
B.1 Functions and Operators used in the Formal Semantics
B.2 Mapping of Overloaded Internal Functions
C Importing Schemas
C.1 Introduction
C.1.1 Features
C.1.2 Organization
C.1.3 Main mapping rules
C.1.4 Special attributes
C.1.4.1 use, default, and fixed
C.1.4.2 minOccurs, maxOccurs, minLength, maxLength, and length
C.1.4.3 mixed
C.1.4.4 nillable
C.1.4.5 substitutionGroup
C.1.5 Anonymous type names
C.2 Schemas as a whole
C.2.1 Schema
C.2.2 Include
C.2.3 Redefine
C.2.4 Import
C.3 Attribute Declarations
C.3.1 Global attributes declarations
C.3.2 Local attribute declarations
C.4 Element Declarations
C.4.1 Global element declarations
C.4.2 Local element declarations
C.5 Complex Type Definitions
C.5.1 Global complex type
C.5.2 Local complex type
C.5.3 Complex type with simple content
C.5.4 Complex type with complex content
C.6 Attribute Uses
C.7 Attribute Group Definitions
C.7.1 Attribute group definitions
C.7.2 Attribute group reference
C.8 Model Group Definitions
C.9 Model Groups
C.9.1 All groups
C.9.2 Choice groups
C.9.3 Sequence groups
C.10 Particles
C.10.1 Element reference
C.10.2 Group reference
C.11 Wildcards
C.11.1 Attribute wildcards
C.11.2 Element wildcards
C.12 Identity-constraint Definitions
C.13 Notation Declarations
C.14 Annotation
C.15 Simple Type Definitions
C.15.1 Global simple type definition
C.15.2 Local simple type definition
C.15.3 Simple type content
D References
D.1 Normative References
D.2 Non-normative References
D.3 Background References
E Auxiliary Judgments for Validation (Non-Normative)
E.1 Judgments for the validate expression
E.1.1 Type resolution
E.1.2 Interleaving
E.1.3 Attribute filtering
E.1.4 Erasure
E.1.4.1 Simply erases
E.1.4.2 Erases
E.1.5 Annotate
E.1.5.1 Simply annotate
E.1.5.2 Nil-annotate
E.1.5.3 Annotate
F Revision Log (Non-Normative)
F.1 4 April 2005
F.2 3 June 2005
This document defines the formal semantics of XQuery 1.0 and XPath 2.0. The present document is part of a set of documents that together define the XQuery 1.0 and XPath 2.0 languages:
[XQuery 1.0: A Query Language for XML] introduces the XQuery 1.0 language, defines its capabilities from a user-centric view, and defines the language syntax.
[XML Path Language (XPath) 2.0] introduces the XPath 2.0 language, defines its capabilities from a user-centric view, and defines the language syntax.
[Functions and Operators] lists the functions and operators defined for the [XPath/XQuery] language and specifies the required types of their parameters and return value.
[Data Model] formally specifies the data model used by [XPath/XQuery] to represent the content of XML documents. The [XPath/XQuery] language is formally defined by operations on this data model.
[Data Model Serialization] specifies how [XPath/XQuery] data model values are serialized into XML.
The scope and goals for the [XPath/XQuery] language are discussed in the charter of the W3C [XSL/XML Query] Working Group and in the [XPath/XQuery] requirements [XML Query 1.0 Requirements].
This document defines the semantics of [XPath/XQuery] by giving a precise formal meaning to each of the expressions of the [XPath/XQuery] specification in terms of the [XPath/XQuery] data model. This document assumes that the reader is already familiar with the [XPath/XQuery] language. This document defines the formal semantics for XPath 2.0 only when the XPath 1.0 backward compatibility rules are not in effect.
Two important design aspects of [XPath/XQuery] are that it is functional and that it is typed. These two aspects play an important role in the [XPath/XQuery] Formal Semantics.
[XPath/XQuery] is a functional language. [XPath/XQuery] is built from expressions, rather than statements. Every construct in the language (except for the XQuery query prolog) is an expression and expressions can be composed arbitrarily. The result of one expression can be used as the input to any other expression, as long as the type of the result of the former expression is compatible with the input type of the latter expression with which it is composed. Another characteristic of a functional language is that variables are always passed by value, and a variable's value cannot be modified through side effects.
[XPath/XQuery] is a typed language. Types can be imported from one or more XML Schemas that describe the input documents and the output document, and the [XPath/XQuery] language can then perform operations based on these types. In addition, [XPath/XQuery] supports static type analysis. Static type analysis infers the output type of an expression based on the type of its input expressions. In addition to infering the type an an expression for the user, static typing allows early detection of type errors, and can be used as the basis for certain classes of optimization. The [XPath/XQuery] type system captures most of the features of [Schema Part 1], including global and local element and attribute declarations, complex and simple type definitions, named and anonymous types, derivation by restriction, extension, list and union, substitution groups, and wildcard types. It does not model uniqueness constraints and facet constraints on simple types.
This document is organized as follows. [2 Preliminaries] introduces the notations used to define the [XPath/XQuery] Formal Semantics. These include the formal notations for values in the [XPath/XQuery] data model and for types in XML Schema. The next three sections: [3 Basics], [4 Expressions], and [5 Modules and Prologs] have the same structure as the corresponding sections in the [XQuery 1.0: A Query Language for XML] and [XML Path Language (XPath) 2.0] documents. This allows the reader to quickly find the formal definition of a particular language construct. [3 Basics] defines the semantics for basic [XPath/XQuery] concepts, and [4 Expressions] defines the dynamic and static semantics of each [XPath/XQuery] expression. [5 Modules and Prologs] defines the semantics of the [XPath/XQuery] prolog. [7 Additional Semantics of Functions] defines the static semantics of several functions in [Functions and Operators] and gives the dynamic and static semantics of several supporting functions used in this document. The remaining sections, [8 Auxiliary Judgments] and [C Importing Schemas], contain material that supports the formal semantics of [XPath/XQuery]. [8 Auxiliary Judgments] defines formal judgments that relate data model values to types, that relate types to types, and that support the formal definition of validation. These judgments are used in the definition of expressions in [4 Expressions]. Lastly, [C Importing Schemas], specifies how XML Schema documents are imported into the [XPath/XQuery] type system and relates XML Schema types to the [XPath/XQuery] type system.
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.]
A language aspect described in this specification as implementation-defined or implementation dependent may be further constrained by the specifications of a host language in which XPath is embedded.
This document contains the normative static semantics of [XPath/XQuery]. The static semantics rules in [3 Basics], [4 Expressions], [5 Modules and Prologs], and [7 Additional Semantics of Functions] are normative. [3.1.1 Static Context] is normative, because it defines the static context used in the static typing rules. [8 Auxiliary Judgments] is normative, because it contains all the judgments necessary for defining SequenceType Matching.
The dynamic semantics of [XPath/XQuery] are normatively defined in [XQuery 1.0: A Query Language for XML] and [XML Path Language (XPath) 2.0]. In this document, the dynamic semantic rules in [3 Basics], [4 Expressions], and [5 Modules and Prologs], the examples and material labeled as "Note" are provided for explanatory purposes and are not normative.
The mapping rules from XML Schema to the XQuery type system provided in [C Importing Schemas], and the formal semantics of XML Schema validation in [E Auxiliary Judgments for Validation] are informative and do not handle every feature of XML Schema.
This section provides the background necessary to understand the Formal Semantics, introduces the notations that are used, and explains its relationship to other documents.
Why a Formal Semantics? The goal of the formal semantics is to complement the [XPath/XQuery] specification ([XQuery 1.0: A Query Language for XML] and [XML Path Language (XPath) 2.0]), by defining the meaning of [XPath/XQuery] expressions with mathematical rigor.
A rigorous formal semantics clarifies the intended meaning of the English specification, ensures that no corner cases are left out, and provides a reference for implementation.
Why use formal notations? Rigor is achieved by the use of formal notations to represent [XPath/XQuery] objects such as expressions, XML values, and XML Schema types, and by the systematic definition of the relationships between those objects to reflect the meaning of the language. In particular, the dynamic semantics relates [XPath/XQuery] expressions to the XML value to which they evaluate, and the static semantics relates [XPath/XQuery] expressions to the XML Schema type that is inferred for that expression.
The Formal Semantics uses several kinds of formal notations to define the relationships between [XPath/XQuery] expressions, XML values, and XML Schema types. This section introduces the notations for judgments, inference rules, and mapping rules as well as the notation for environments, which implement the dynamic and static contexts. The reader already familiar with these notations can skip this section and continue with [2.3 XML Values].
Grammar productions are used to describe "objects" (values, types, [XPath/XQuery] expressions, etc.) manipulated by the Formal Semantics. The Formal Semantics makes use of several kinds of grammar productions: productions from the [XPath/XQuery] grammar itself, productions for a subset of the [XPath/XQuery] language called the XQuery core which is used throughout this document, and other productions used for formal specification only such as for the XQuery type system.
XQuery grammar productions describe the XQuery language and expressions. XQuery productions are identified by a number, which corresponds to their number in the [XQuery 1.0: A Query Language for XML] document, and are marked with "(XQuery)". For instance, the following production describes FLWOR expressions in XQuery.
[33 (XQuery)] | FLWORExpr |
::= | (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle |
For the purpose of this document, the differences between the XQuery 1.0 and the XPath 2.0 grammars are mostly irrelevant. By default, this document uses XQuery 1.0 grammar productions. Whenever the grammar for XPath 2.0 differs from the one for XQuery 1.0, the corresponding XPath 2.0 productions are also given. XPath productions are identified by a number, which corresponds to their number in [XML Path Language (XPath) 2.0], and are marked with "(XPath)". For instance, the following production describes for expressions in XPath.
[4 (XPath)] | ForExpr |
::= | SimpleForClause "return" ExprSingle |
XQuery Core grammar productions describe the XQuery Core. The Core grammar is given in [A Normalized core grammar]. Core productions are identified by a number, which corresponds to their number in [A Normalized core grammar], and are marked with "(Core)". For instance, the following production describes the simpler form of the "FLWOR" expression in the XQuery Core.
[32 (Core)] | FLWORExpr |
::= | (ForClause | LetClause) "return" ExprSingle |
The Formal Semantics manipulates "objects" (values, types, expressions, etc.) for which there is no existing grammar production in the [XQuery 1.0: A Query Language for XML] document. In these cases, specific grammar productions are introduced. Notably, additional productions are used to describe values in the [Data Model], and to describe the [XPath/XQuery] type system. Formal Semantics productions are identified by a number, and are marked by "(Formal)". For instance, the following production describes global type definitions in the [XPath/XQuery] type system.
[40 (Formal)] | Definition |
::= | ("define" "element" ElementName Substitution? Nillable? TypeReference) |
Note that grammar productions that are specific to the Formal Semantics (i.e., marked with "(Formal)") are not part of [XPath/XQuery]. They are not accessible to the user and are only used in the course of defining the languages' semantics.
Grammar non-terminals are used extensively in this document to represent objects in inference rules (see the next section). As a convenience, non-terminals used in inference rules link to the appropriate grammar production.
The basic building block of the formal specification is called a judgment. A judgment expresses whether a property holds or not.
For example:
Notation
The judgment
holds if the object Painting is beautiful.
Notation
Here are three judgments that are used extensively in this document.
The judgment
holds if the expression Expr yields (or evaluates to) the value Value.
The judgment
holds when the expression Expr has the type Type.
Most other judgments used in this document are short english sentences intended to reflect their meaning, and written in bold fonts. For instance, the judgment
holds when the expression Expr raises the error Error.
A judgment can contain symbols and patterns.
Symbols are purely syntactic and are used to write the judgment itself. In general, symbols in a judgment are chosen to reflect its meaning. For example, 'is beautiful', '=>' and ':' are symbols, the second and third of which should be read "yields", and "has type" respectively.
Patterns are written with italicized words. The name of a pattern is significant: each pattern name corresponds to an "object" (a value, a type, an expression, etc.) that can be substituted legally for the pattern. By convention, all patterns in the Formal Semantics correspond to grammar non-terminals, and are used to represent entities that can be constructed through application of the corresponding grammar production. For example, Expr represents any [XPath/XQuery] expression, and Value represents any value in the [XPath/XQuery] data model.
When applying the judgment, each pattern must be instantiated to an appropriate sort of "object" (value, type, expression, etc). For example, '3 => 3' and '$x+0 => 3' are both instances of the judgment 'Expr => Value'. Note that in the first judgment, '3' corresponds to both the expression '3' (on the left-hand side of the => symbol) and to the the value '3' (on the right-hand side of the => symbol).
Patterns may appear with subscripts (e.g. Expr1, Expr2) to distinguish different instances of the same sort of pattern. Each distinct pattern must be instantiated to a single "object" (value, type, expression, etc.). If the same pattern occurs twice in a judgment description then it should be instantiated with the same "object". For example, '3 => 3' is an instance of the judgment 'Expr1 => Expr1' but '$x+0 => 3' is not since the two expressions '$x+0' and '3' cannot be both instance of the pattern Expr1. The judgment'$x+0 => 3' is an instance of the judgment 'Expr1 => Expr2'.
Patterns may have a name that is not exactly the name of a grammar production but is based on it. For instance, a BaseTypeName is a pattern that stands for a type name, as would TypeName, or TypeName2. This usage is limited, and only occurs to improve the readability of some of the inference rules.
In some cases, inference rules may need to use the fact that a certain judgment does not hold. We may write not(Judgment) the judgment which holds iff Judgment does not hold.
In some cases, an "object" may take a value within a finite set of pre-determined values. We may write those set of possible value using the in judgment. For instance, the judgment
which holds, if the object Color has either the value blue or the value green.
Inference rules are used to specify whether a judgment holds or not. Inference rules express the logical relation between judgments and describe how complex judgments can be concluded from simpler premise judgments.
A logical inference rule is written as a collection of premises and a conclusion, written respectively above and below a dividing line:
premise1 ... premisen |
|
conclusion |
All premises and the conclusion are judgments. The interpretation of an inference rule is: if all the premise judgments above the line hold, then the conclusion judgment below the line must also hold.
Here is a simple example of inference rule, which uses the example judgment 'Expr => Value' from above:
$x => 0 3 => 3 |
|
$x + 3 => 3 |
This inference rule expresses the following property of the judgment 'Expr => Value': if the variable expression '$x' yields the value '0', and the literal expression '3' yields the value '3', then the expression '$x + 3' yields the value '3'.
An inference rule may have no premises above the line, which means that the expression below the line always holds:
|
3 => 3 |
This inference rule expresses the following property of the judgment 'Expr => Value': evaluating the literal expression '3' always yields the value '3'.
The two above rules are expressed in terms of specific variables and values, but usually rules are more abstract. That is, the judgments they relate contain patterns. Here is a rule that says that for any variable Variable that yields the integer value Integer, adding '0' yields the same integer value:
Variable => Integer |
|
Variable + 0 => Integer |
As in a judgment, each pattern in a particular inference rule must be instantiated to the same "object" within the entire rule. This means that one can talk about "the value of Variable" instead of the more precise "what Variable is instantiated to in (this particular instantiation of) the inference rule".
Logical inference rules use environments to record information computed during static type analysis or dynamic evaluation so that this information can be used by other logical inference rules. For example, the type signature of a user-defined function in a [expression/query] prolog can be recorded in an environment and used by subsequent rules. Similarly, the value assigned to a variable within a "let" expression can be captured in an environment and accessed later on during evaluation when that variable is accessed.
An environment is a dictionary that maps a symbol (e.g., a function name or a variable name) to an "object" (e.g., a function body, a type, a value). One can access information in an environment or update the environment.
If "env" is an environment, then "env(symbol)" denotes the "object" to which symbol is mapped. The notation is intentionally similar to function application, because an environment can be considered a function from the argument symbol to the "object" to which the symbol is mapped.
This document uses environment groups that group related environments. If "group" is an environment group with the environment component "env", then that environment is denoted "group.env" and the value that symbol is mapped to is denoted "group.env(symbol)".
The two main environment groups used in the Formal Semantics are: a dynamic environment group (dynEnv), which models to the [XPath/XQuery]'s dynamic context, and a static environment group (statEnv), which models the [XPath/XQuery]'s static context. Both are defined in [3.1 Expression Context].
For example, dynEnv.varValue denotes the dynamic environment that maps variables to values and dynEnv.varValue(Variable) denotes the value of the variable Variable in the dynamic context.
Environment groups are used in a judgment to capture some of the context in which the judgment is computed, and most judgments are computed assuming that some environment is given. This assumption is denoted by prefixing the judgment with "env |-". The "|-" symbol is called a "turnstile" and is used in almost all inference rules.
For instance, the judgment
is read as: Assuming the dynamic environment group dynEnv, the expression Expr yields the value Value.
Environment groups can be updated, using the following notation:
"group + env(symbol => object) " denotes the new environment group that is identical to group except that the env environment has been updated to map symbol to object. The notation symbol => object indicates that symbol is mapped to object in the new environment.
The following shorthand is also allowed: "group + env( symbol1 => object1 ; ... ; symboln => objectn ) " in which each symbol is mapped to a corresponding object in the new environment.
This notation is equivalent to nested updates, as in " (group + env( symbol1 => object1) + ... ) + env(symboln => objectn)".
Updating an environment creates a copy of the original environment and overrides any previous binding that might exist for the same name and the same group in that environment. Updating the environment is used to capture the scope of a symbol (e.g., for variables, namespace prefixes, etc). For instance, in the following expression
let $x := 1 return let $x := $x + 2 return $x - 3
each let expression changes the dynamic context by binding a new variable to a new value. Each different context is represented by a different environment. The original environment, in which the expression 1
is evaluated, does not contain any binding for variable $x
. This environment is updated a first time with a binding of variable $x
to the value 1
, and this environment is used for the evaluation of the expression $x + 2
. Then it is
updated a second time with a binding of variable $x
to the value 3
, and this environment is used for the evaluation of the expression$x - 3
.
Also, note that there are no operations to remove entries from environments. This is never necessary as updating an environment effectively creates a new extended copy of the original environment, leaving the original environment accessible wherever it is in scope along with the updated copy.
Putting the above notations together, here is an example of an inference rule that occurs later in this document:
This rule is read as follows: if two expressions Expr1 and Expr2 are known to have the static types types Type1 and Type2 (the two premises above the line), then it is the case that the expression below the line "Expr1 , Expr2" must have the static type "Type1, Type2", which is the sequence of types Type1 and Type2. The above inference rule does not modify the (static) environment.
The following rule defines the static semantics of a "let" expression. The binding of the new variable is captured by an update to the varType component of the original static environment.
|
|||
|
|||
statEnv |- let $ VarName := Expr1 return Expr2 : Type2 |
This rule is read as follows: First, because the variable is a QName, it is first expanded into an expanded QName. Second, the type Type1 for the "let" input expression Expr1 is computed. Then the "let" variable with expanded name, expanded-QName with type Type1 is added into the varType component of the static environment group statEnv. Finally, the type Type2 of Expr2 is computed in that new environment.
Each inference rule describes a fragment of the semantics for a given expression. Here is how those rules are combined. Consider the following expression.
let $x := 1 return ($x,$x)
We have just seen the static typing rule for the let clause and sequence construction. To handle this expression completely, we need inference rules for integer literals and variable access. Those two rules are as follows.
|
||
|
||
|
With this set of rules, we can compute the type of the expression above in a bottom-up fashion, i.e., starting with the sub-expressions. The resulting type inference proceeds as follows.
statEnv0 = () statEnv0 |- 1 : xs:integer statEnv1 = ($x -> 1) statEnv1 |- $x : xs:integer statEnv1 |- $x : xs:integer statEnv1 |- ($x,$x) : xs:integer,xs:integer statEnv0 |- let $x := 1 return ($x,$x) : xs:integer,xs:integer
This example illustrates how each rule is applied to individual sub-expressions, and how the environment is used to maintain the relevant context information.
The Formal Semantics does not formally specify the adjustment of relative URIs according to a base URI. All URIs used in this document are assumed to be absolute URIs.
The Formal Semantics uses the following namespace prefixes.
fn:
for functions and operators from the [Functions and Operators] document.
xs:
for XML Schema components and built-in types.
xdt:
for [XPath/XQuery] built-in types.
All these prefixes are assumed to be bound to the appropriate URIs.
In addition, the Formal Semantics uses the following special prefixes for specification purposes.
dm: for accessors of the [Data Model].
op: for operators in [Functions and Operators].
fs: for functions and types defined in the formal semantics.
These prefixes are always italicized to emphasize that the corresponding functions, variables, and types are abstract: they are not and cannot be made accessible in [XPath/XQuery]. None of these special prefixes are given a URI.
The [XPath/XQuery] language is defined over values of the [XPath/XQuery] data model. The [XPath/XQuery] data model is defined normatively in [Data Model]. We define the formal notation that is used in this document to describe and manipulate values in inference rules. Formal values are used for specification purposes only and are not exposed to the [XPath/XQuery] user.
This section gives the grammar for formal values, along with a summary of the corresponding data model properties. In the context of this document, all constraints on values that are specified in [Data Model] are assumed to hold.
A value is a sequence of zero or more items. An item is either an atomic value or a node.
An atomic value is a value in the value space of an atomic type, labeled with the name of that atomic type. An atomic type is either a primitive or derived atomic type according to XML Schema [Schema Part 2], xdt:untypedAtomic
, or xdt:anyAtomicType
.
A node is either an element, an attribute, a document, a text, a comment, or a processing-instruction node.
Element nodes have a type annotationXQ and contain a complex value or a simple value. Attribute nodes have a type annotationXQ and contain a simple value. Text nodes always contain one string value of type xdt:untypedAtomic
, therefore the corresponding type annotation is omitted in
the formal notation of a text node. Document nodes do not have a type annotation and contain a sequence of element, text, comment, or processing-instruction nodes.
A simple value is a sequence of atomic values.
A complex value is a sequence of attribute nodes followed by a sequence of element, text, comment, or processing-instruction nodes.
A type annotationXQ can be either the QName of a declared type or an anonymous type. An anonymous type corresponds to an XML Schema type for which the schema writer did not provide a name. Anonymous type names are not visible to the user, but are generated during schema validation and used to annotate nodes in the data model. By convention, anonymous type names are written using the fs: Formal Semantics prefix: fs:anon0, fs:anon1, etc.
Formal values are defined by the following grammar.
[7 (Formal)] | Value |
::= | Item |
[21 (Formal)] | Item |
::= | NodeValue |
[22 (Formal)] | AtomicValue |
::= | AtomicValueContent TypeAnnotation? |
[1 (Formal)] | AtomicValueContent |
::= | String |
[2 (Formal)] | TypeAnnotation |
::= | "of" "type" TypeName |
[9 (Formal)] | ElementValue |
::= | "element" ElementName "nilled"? TypeAnnotation? "{" Value "}" ("{" NamespaceBindings "}")? |
[10 (Formal)] | AttributeValue |
::= | "attribute" AttributeName TypeAnnotation? "{" SimpleValue "}" |
[8 (Formal)] | SimpleValue |
::= | AtomicValue |
[11 (Formal)] | DocumentValue |
::= | "document" "{" Value "}" |
[13 (Formal)] | CommentValue |
::= | "comment" "{" String "}" |
[14 (Formal)] | ProcessingInstructionValue |
::= | "processing-instruction" QName "{" String "}" |
[12 (Formal)] | TextValue |
::= | "text" "{" String "}" |
[20 (Formal)] | NodeValue |
::= | ElementValue |
[3 (Formal)] | ElementName |
::= | QName |
[6 (Formal)] | AttributeName |
::= | QName |
[23 (Formal)] | TypeName |
::= | QName |
[15 (Formal)] | NamespaceBindings |
::= | NamespaceBinding ("," NamespaceBinding)* |
[17 (Formal)] | NamespaceBinding |
::= | "namespace" NCName "{" String "}" |
Notation
In that grammar, "String" indicates the value space of xs:string
, "Decimal" indicates the value space of xs:decimal
, etc.
Element (resp. attributes) without type annotations, are assumed to have the type annotation xs:anyType
(resp. xs:anySimpleType
). Atomic values without type annotations, are assumed to have a type annotation which is the base type for the corresponding value. For instance, "Hello, World!"
is equivalent to "Hello, World!" of type xs:string
.
Untyped elements (e.g., from well-formed documents) have the type annotationXQ xdt:untyped
, untyped attributes have the type annotationXQ xdt:untypedAtomic
, and untyped atomic values have the type annotationXQ xdt:untypedAtomic
.
An element has an optional "nilled" marker. This marker can only be present if the element has been validated against an element type in the schema which is "nillable", and the element has no content and an attribute xsi:nil
set to "true"
.
An element also has a sequence of namespace bindings, which are the set of in-scope namespaces for that element. Each namespace binding is a prefix, URI pair. Elements without namespace bindings are assumed to have an empty set of in-scope namespaces.
Note:
In [XPath], 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 [XML Path Language (XPath) 2.0]. XQuery does not support the namespace axis and does not represent namespace bindings in the form of nodes.
In examples, we omit the namespace bindings when they are empty. For example, the following two values are the same (note that the xs
and xdt
prefixes are built-in):
element weight of type xs:integer { text { "42" } } {} element weight of type xs:integer { text { "42" } }
The same rule about constructing sequences apply to the values described by that grammar. Notably sequences are automatically flattened. For example, the sequence (10, (1, 2), (), (3, 4))
is equivalent to the sequence (10, 1, 2, 3, 4)
.
When the context is clear, we may omit the type annotationXQ on literal values. For instance:
"Hello World!" instead of "Hello World!" of type xs:string 10 instead of 10 of type xs:integer
A well-formed document
<fact>The cat weighs <weight units="lbs">12</weight> pounds.</fact>
In the absence of a Schema, this document is represented as
element fact of type xdt:untyped { text { "The cat weighs " }, element weight of type xdt:untyped { attribute units of type xdt:untypedAtomic { "lbs" of type xdt:untypedAtomic } text { "12" } }, text { " pounds." } }
A document before and after validation.
<weight xsi:type="xs:integer">42</weight>
The formal model for values can represent values before and after validation. Before validation, this element is represented as:
element weight of type xdt:untyped { attribute xsi:type of type xdt:untypedAtomic { "xs:integer" of type xdt:untypedAtomic }, text { "42" } }
After validation, this element is represented as:
element weight of type xs:integer { attribute xsi:type of type xs:QName { "xs:integer" of type xs:QName }, 42 of type xs:integer }
An element with a list type
<sizes>1 2 3</sizes>
Before validation, this element is represented as:
element sizes of type xdt:untyped { text { "1 2 3" } }
Assume the following Schema.
<xs:element name="sizes" type="sizesType"/> <xs:simpleType name="sizesType"> <xs:list itemType="sizeType"/> </xs:simpleType> <xs:simpleType name="sizeType"> <xs:restriction base="xs:integer"/> </xs:simpleType>
After validation against this Schema, the element is represented as:
element sizes of type sizesType { 1 of type sizeType, 2 of type sizeType, 3 of type sizeType }
An element with an anonymous type
<sizes>1 2 3</sizes>
Before validation, this element is represented as:
element sizes of type xdt:untyped { text { "1 2 3" } }
Assume the following Schema.
<xs:element name="sizes"> <xs:simpleType> <xs:list itemType="xs:integer"/> </xs:simpleType> </xs:element>
After validation, this element is represented as:
element sizes of type fs:anon1 { 1 of type xs:integer, 2 of type xs:integer, 3 of type xs:integer }
where fs:anon1 stands for the internal anonymous name generated by the system for the sizes
element.
An nillable element with xsi:type
set to true:
<sizes xsi:nil="true"/>
Before validation, this element is represented as:
element sizes of type xdt:untyped { attribute xsi:nil of type xdt:untypedAtomic { "true" as xdt:untypedAtomic } }
Assume the following Schema.
<xs:element name="sizes" type="sizesType" nillable="true"/>
After validation against this Schema, the element is represented as:
element sizes nilled of type sizesType { attribute xsi:nil of type xs:boolean { true as xs:boolean } }
An element with a union type
<sizes>1 two 3 four</sizes>
Before validation, this element is represented as:
element sizes of type xdt:untyped { text { "1 two 3 four" } }
Assume the following Schema:
<xs:element name="sizes" type="sizesType"/> <xs:simpleType name="sizesType"> <xs:list itemType="sizeType"/> </xs:simpleType> <xs:simpleType name="sizeType"> <xs:union memberType="xs:integer xs:string"/> </xs:simpleType>
After validation against this Schema, the element is represented as:
element sizes of type sizesType { 1 of type xs:integer, "two" of type xs:string, 3 of type xs:integer, "four" of type xs:string }
The [XPath/XQuery] type system is used in the specification of the dynamic and of the static semantics of [XPath/XQuery]. This section introduces formal notations for describing types.
The [XPath/XQuery] type system is based on [Schema Part 1] and [Schema Part 2]. [Schema Part 1] and [Schema Part 2] specify normatively the type information available in [XPath/XQuery]. We define the formal notation that is used in this document to describe and manipulate types in inference rules. Formal types are used for specification purposes only and are not exposed to the [XPath/XQuery] user.
Representation of content models. For the purpose of static typing, the [XPath/XQuery] type system only describes minOccurs, maxOccurs, and minLength, maxLength on list types for the occurrences that correspond to the DTD operators +
, *
, and ?
. Choices are represented using the DTD operator |
. All groups are represented using the interleaving operator (&
).
Representation of anonymous types. To clarify the semantics, the [XPath/XQuery] type system makes all anonymous types explicit.
Representation of XML Schema simple type facets and identity constraints. For simplicity, XML Schema simple type facets and identity constraints are not formally represented in the [XPath/XQuery] type system. However, an [XPath/XQuery] implementation supporting XML Schema import and validation must must take simple type facets and identity constraints into account.
The mapping from XML Schema into the [XPath/XQuery] type system is given in [C Importing Schemas]. The rest of this section is organized as follows. [2.4.2 Item types] describes types items, [2.4.3 Content models] describes content models, and [2.4.4 Top level definitions] describe top-level type declarations.
An item type is either an atomic type, an element type, an attribute type, a document node type, a text node type, a comment node type, or a processing instruction type. We distinguish between document nodes, attribute nodes, and nodes that can occur in element content (elements, comments, processing instructions, and text nodes), as we need to refer to element content types later in the formal semantics.
[26 (Formal)] | FormalItemType |
::= | AtomicTypeName | NodeType |
[29 (Formal)] | AtomicTypeName |
::= | QName |
[27 (Formal)] | NodeType |
::= | DocumentType |
[28 (Formal)] | ElementContentType |
::= | ElementType |
[30 (Formal)] | ElementType |
::= | "element" ElementName? TypeSpecifier? |
[31 (Formal)] | TypeSpecifier |
::= | Nillable? TypeReference |
[32 (Formal)] | AttributeType |
::= | "attribute" AttributeName? TypeReference? |
[33 (Formal)] | Nillable |
::= | "nillable" |
[37 (Formal)] | TypeReference |
::= | "of" "type" TypeName |
[49 (Formal)] | DocumentType |
::= | "document" ("{" Type "}")? |
An element or attribute type has an optional name and an optional type reference. A name alone corresponds to a reference to a global element or attribute declaration. A name with a type reference corresponds to a local element or attribute declaration. The word "element" or "attribute" alone refers to the wildcard types for any element or any attribute. In addition, an element type has an optional nillable flag that indicates whether the element can be nilled or not.
A document type has an optional content type. If no content type is given, then the type is treated as being the wildcard type for documents, i.e., a sequence of text and element nodes. For consistency with element nodes, PIs and comments are not indicated in that wildcard type, but may occur in instances.
Note
Generic node types (e.g., node()
) such as used in the SequenceType production, are interpreted in the type system as union types (e.g., element | attribute | text | comment | processing-instruction
) and therefore do not appear here. The semantics of sequence types is described in [3.5.4 SequenceType Matching].
Examples
The following is a text node type
text
The following is a type for all elements
element
The following is a type for all elements of type string
element of type xs:string
The following is a type for a nillable element of type string and with name size
element size nillable of type xs:string
The following is a reference to a global attribute declaration
attribute sizes
The following is a type for elements with anonymous type fs:anon1:
element sizes of type fs:anon1
Following XML Schema, types in [XPath/XQuery] are composed from item types by optional, one or more, zero or more, all group, sequence, choice, empty sequence (written empty
), or empty choice (written none
).
The type empty
matches the empty sequence. The type none
matches no values. none
is the identity for choice, that is (Type | none
) = Type)). The type none
is the static type for [7.2.9 The fn:error function].
[24 (Formal)] | Type |
::= | FormalItemType |
[25 (Formal)] | Occurrence |
::= | "*" | "+" | "?" |
The [XPath/XQuery] type system includes three binary operators on types: ",", "|" and "&", corresponding respectively to sequence, choice and all groups in Schema. The [XPath/XQuery] type system includes three unary operators on types: "*", "+", and "?", corresponding respectively to zero or more instances of the type, one or more instances of the type, or an optional instance of the type.
The "&" operator builds the "interleaved product" of two types. The type Type1 &
Type2 matches any sequence that is an interleaving of a sequence that matches Type1 and a sequence that matches Type2. The
interleaved product captures the semantics of all groups in XML Schema, but it more general has it applies to arbitrary types. All groups in XML Schema are restricted to apply only on global or local element declarations with minOccurs 0 or 1, and maxOccurs 1.
The "&" operator builds the "interleaved product" of two types. The type Type1 & Type2 matches any sequence that is an interleaving of two sequences of items, the first one matching Type1 and the second matching Type2. Where the interleaving of two sequences of items Value1 and Value2 is any sequence Value0 such that there is an ordered partition of Value0 into the two sub-sequences Value1 and Value2.
For example, consider the types Type1 = xs:integer
,xs:integer
,xs:integer
and Type2 = xs:string
,xs:string
. Value1 = (1,2,3)
matches the type Type1 and
Value2 = ("a","b")
matches the type Type2. Any of the following Value0 are interleavings of Value1 and Value2, and therefore match the type (Type1 & Type2):
Value0 = (1,2,3,"a","b") Value0 = (1,2,"a",3,"b") Value0 = (1,2,"a","b",3) Value0 = (1,"a",2,3,"b") Value0 = (1,"a",2,"b",3) Value0 = (1,"a","b",2,3) Value0 = ("a",1,2,3,"b") Value0 = ("a",1,2,"b",3) Value0 = ("a",1,"b",2,3) Value0 = ("a","b",1,2,3)
Types precedence order. To improve readability when writing types, we assume the following precedence order between operators on types.
# | Operator | Associativity |
---|---|---|
1 | | (choice) | left-to-right |
2 | & (interleaving) | right-to-left |
3 | , (sequence) | left-to-right |
4 | *, +, ? (occurrence) | left-to-right |
Parenthesis can be used to enforce precedence. For instance
xs:string | xs:integer, xs:float*
is equivalent to
xs:string | (xs:integer, (xs:float*))
and a different precedence can be obtained by writing
((xs:string | xs:integer), xs:float)*
Examples
A sequence of elements
The "," operator builds the "sequence" of two types. For example,
element title of type xs:string, element year of type xs:integer
is a sequence of an element title of type string followed by an element year of type integer.
The union of two element types
The "|" operator builds the "union" of two types. For example,
element editor of type xs:string | element bib:author
means either an element editor of type string, or a reference to the global element bib:author
.
An all group of two elements
The "&" operator builds the "interleaved product" of two types. For example,
(element a & element b) = element a, element b | element b, element a
which specifies that the a
and b
elements can occur in any order.
An empty type
The following type matches the empty sequence.
empty
A sequence of zero or more elements
The following type matches zero or more elements each of which can be a surgeon
or a plumber
.
(element surgeon | element plumber)*
Top level definitions correspond to global element declarations, global attribute declarations and type definitions in XML Schema.
[41 (Formal)] | Definitions |
::= | Definition* |
[40 (Formal)] | Definition |
::= | ("define" "element" ElementName Substitution? Nillable? TypeReference) |
[42 (Formal)] | Substitution |
::= | "substitutes" "for" ElementName |
[34 (Formal)] | TypeDerivation |
::= | ComplexTypeDerivation | AtomicTypeDerivation |
[35 (Formal)] | ComplexTypeDerivation |
::= | Derivation? Mixed? "{" Type? "}" |
[36 (Formal)] | AtomicTypeDerivation |
::= | "restricts" AtomicTypeName |
[38 (Formal)] | Derivation |
::= | ("restricts" TypeName) |
[39 (Formal)] | Mixed |
::= | "mixed" |
A type definition has a name (possibly anonymous) and a type derivation. In the case of a complex type, or a simple type derived by list or union, derivation indicates if the type is derived by extension or restriction from its base type, gives its content model, and an optional flag indicating if it has mixed content. In the case of an atomic type, it just indicates from which type it is derived. When the type derivation is omitted, the type derives by restriction from xs:anyType
, as
in:
define type Bib { element book* } = define type Bib restricts xs:anyType { element book* }
Empty content can be indicated with the explicit empty sequence, or omitted, as in:
define type Bib { } = define type Bib { empty }
Global element and attribute declarations always have a name and a reference to a (possibly anonymous) type. A global element declaration also may declare a substitution group for the element and whether the element is nillable.
Examples
A type declaration with one element name of type xs:string
follows by one or more elements street of type xs:string
.
define type Address { element name of type xs:string, element street of type xs:string* }
A type declaration with complex content derived by extension
define type USAddress extends Address { element zip name of type xs:integer }
A type declaration with mixed content
define type Section mixed { (element h1 of type xs:string | element p of type xs:string | element div of type Section)* }
A type declaration with simple content derived by restriction
define type SKU restricts xs:string
An element declaration
define element address of type Address
An element declaration with a substitution group
define element usaddress substitutes for address of type USAddress
An element declaration which is nillable
define element zip nillable of type xs:integer
Here is a schema describing purchase orders from [XML Schema Part 0].
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:annotation> <xsd:documentation xml:lang="en"> Purchase order schema for Example.com. Copyright 2000 Example.com. All rights reserved. </xsd:documentation> </xsd:annotation> <xsd:element name="purchaseOrder" type="PurchaseOrderType"/> <xsd:element name="comment" type="xsd:string"/> <xsd:complexType name="PurchaseOrderType"> <xsd:sequence> <xsd:element name="shipTo" type="USAddress"/> <xsd:element name="billTo" type="USAddress"/> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="items" type="Items"/> </xsd:sequence> <xsd:attribute name="orderDate" type="xsd:date"/> </xsd:complexType> <xsd:complexType name="USAddress"> <xsd:sequence> <xsd:element name="name" type="xsd:string"/> <xsd:element name="street" type="xsd:string"/> <xsd:element name="city" type="xsd:string"/> <xsd:element name="state" type="xsd:string"/> <xsd:element name="zip" type="xsd:decimal"/> </xsd:sequence> <xsd:attribute name="country" type="xsd:NMTOKEN" fixed="US"/> </xsd:complexType> <xsd:complexType name="Items"> <xsd:sequence> <xsd:element name="item" minOccurs="0" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="productName" type="xsd:string"/> <xsd:element name="quantity"> <xsd:simpleType> <xsd:restriction base="xsd:positiveInteger"> <xsd:maxExclusive value="100"/> </xsd:restriction> </xsd:simpleType> </xsd:element> <xsd:element name="USPrice" type="xsd:decimal"/> <xsd:element ref="comment" minOccurs="0"/> <xsd:element name="shipDate" type="xsd:date" minOccurs="0"/> </xsd:sequence> <xsd:attribute name="partNum" type="SKU" use="required"/> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> <!-- Stock Keeping Unit, a code for identifying products --> <xsd:simpleType name="SKU"> <xsd:restriction base="xsd:string"> <xsd:pattern value="\d{3}-[A-Z]{2}"/> </xsd:restriction> </xsd:simpleType> </xsd:schema>
Here is the mapping of the above schema into the [XPath/XQuery] type system.
declare namespace xsd = "http://www.w3.org/2001/XMLSchema"; define element purchaseOrder of type PurchaseOrderType; define element comment of type xsd:string; define type PurchaseOrderType { attribute orderDate of type xsd:date?, element shipTo of type USAddress, element billTo of type USAddress, element comment?, element items of type Items }; define type USAddress { attribute country of type xsd:NMTOKEN, element name of type xsd:string, element street of type xsd:string, element city of type xsd:string, element state of type xsd:string, element zip of type xsd:decimal }; define type Items { attribute partNum of type SKU, element item of type fs:anon1* }; define type fs:anon1 { element productName of type xsd:string, element quantity of type fs:anon2, element USPrice of type xsd:decimal, element comment?, element shipDate of type xsd:date? }; define type fs:anon2 restricts xsd:positiveInteger; define type SKU restrict xsd:string;
Note that the two anonymous types in the item
element declarations are mapping to types with names fs:anon1 and fs:anon2.
The following additional definitions illustrate how more advanced XML Schema features (a complex type derived by extension, an anonymous simple type derived by restriction, and substitution groups) are represented in the [XPath/XQuery] type system.
<complexType name="NYCAddress"> <complexContent> <extension base="USAddress"> <sequence> <element ref="apt"/> </sequence> </extension> </complexContent> </complexType> <element name="apt"> <xsd:simpleType> <xsd:restriction base="xsd:positiveInteger"> <xsd:maxExclusive value="10000"/> </xsd:restriction> </xsd:simpleType> </element> <element name="usaddress" substitutionGroup="address" type="USAddress"/> <element name="nycaddress" substitutionGroup="usaddress" type="NYCAddress"/>
The above definitions are mapped into the [XPath/XQuery] type system as follows:
define type NYCAddress extends USAddress { element apt } define element apt of type fs:anon3 define type fs:anon3 restricts xsd:positiveInteger define element usaddress substitutes for address of type USAddress define element nycaddress substitutes for usaddress of type NYCAddress
The [Functions and Operators] document defines built-in functions available in [XPath/XQuery]. A number of these functions are used to define the [XPath/XQuery] semantics; those functions are listed in [B.1 Functions and Operators used in the Formal Semantics].
Many functions in the [Functions and Operators] document are generic: they perform operations on arbitrary components of the data model, e.g., any kind of node, or any sequence of items. For instance, the fn:unordered
returns its input sequence in an implementation-dependent order. The signature of the fn:unordered
function takes arbitrary items as input and output:
fn:unordered($sourceSeq as item()*) as item()*
As defined, this signature provides little useful type information. For such functions, better type information can often be obtained by having the output type depend on the type of input parameters. For instance, if the function fn:unordered
is applied on a sequence of a
elements, the resulting sequence is also a collection of either a
elements.
In order to provide better static typing for those functions, specific typing rules are given in [7 Additional Semantics of Functions].
The organization of this section parallels the organization of Section 2 BasicsXQ.
Introduction
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 the static context and the dynamic context. This section specifies the environments that represent the context information used by [XPath/XQuery] expressions.
The environment group statEnv denotes the environments that are available during static analysis. Static analysis may extend parts of the static environment. The static environment is also available during dynamic evaluation.
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. This constraint is formalized in [3.3 Error Handling].
The following environments are part of the static environment group:
statEnv.xpath1.0_compatibility |
|
|||||
statEnv.namespace |
|
|||||
statEnv.default_elem_namespace |
|
|||||
statEnv.default_function_namespace |
|
|||||
statEnv.typeDefn |
|
|||||
statEnv.elemDecl |
|
|||||
statEnv.attrDecl |
|
|||||
statEnv.varType |
|
|||||
statEnv.funcType |
|
|||||
statEnv.collations |
|
|||||
statEnv.defaultCollation |
|
|||||
statEnv.constructionMode |
|
|||||
statEnv.orderingMode |
|
|||||
statEnv.defaultEmptySequenceOrder |
|
|||||
statEnv.boundarySpace |
|
|||||
statEnv.copyNamespacesMode |
|
|||||
statEnv.baseUri |
|
|||||
statEnv.docType |
|
|||||
statEnv.collectionType |
|
|||||
statEnv.defaultCollectionType |
|
Note that the boundary-space behavior is not formally specified in this document.
Environments have an initial state when [expression/query] processing begins, containing, for example, the function signatures of all built-in functions. The initial values for the static context are defined in Section C Context ComponentsXQ and Section C Context ComponentsXP and is denoted by statEnvDefault in the Formal Semantics.
Here is an example that shows how the static environment is modified in response to a namespace definition.
|
||
|
||
statEnv |- declare namespace NCName = URI Expr* |
This rule reads as follows: "the phrase on the bottom (a namespace declaration in the query prolog followed by a sequence of expressions) is well-typed (accepted by the static type inference rules) within an environment statEnv if the sequence of expressions above the line is well-typed in the environment obtained from statEnv by adding the namespace declaration".
The helper function fs:active_ns
(statEnv) returns all the active in-scope namespaces in the given static environment.
For each attribute and element node in Value, such that the node has name expanded-QName in the namespace URI, the helper function fs:get_static_ns_from_items
(statEnv, Value) returns the in-scope namespace that corresponds to URI. This is a reverse-lookup on
statEnv.namespace by URI.
A common use of the static environment is to expand a QName by looking up the URI that corresponds to the QName's namespace prefix in the statEnv.namespace environment and by constructing an expanded-QNameDM, which contains the URI and the QName's local part. Element and type names may be in the null namespace, that is,
there is no URI associated with their namespace prefix. The null namespace is denoted by the special value #NULL-NAMESPACE
.
The auxiliary judgments below expand an element, type, attribute, variable, or function QName by looking up the namespace prefix in statEnv.namespace or, if the QName is unqualified, by using the appropriate default namespace.
Notation
The judgment
holds when the element or type QName expands to the given expanded QName.
The judgment
holds when the attribute QName expands to the given expanded QName.
The judgment
holds when the variable QName expands to the given expanded QName.
The judgment
holds when the function QName expands to the given expanded QName.
Semantics
An element or type QName consisting of a prefix NCName and a local part NCName expands to the URI (or the null namespace) corresponding to that prefix and the local part.
statEnv.namespace(NCName1) = URI-or-#NULL-NAMESPACE |
|
statEnv |- NCName1:NCName2of elem/type expands to (URI-or-#NULL-NAMESPACE,NCName2) |
An element or type QName consisting only of a local part NCName expands to the default element/type namespace and the local part.
statEnv.default_elem_namespace = URI-or-#NULL-NAMESPACE |
|
statEnv |- NCName of elem/type expands to (URI-or-#NULL-NAMESPACE,NCName) |
An attribute QName consisting of a prefix NCName and a local part NCName expands to the URI (or the null namespace) corresponding to the prefix and the local part.
statEnv.namespace(NCName1) = URI-or-#NULL-NAMESPACE |
|
statEnv |- NCName1:NCName2of attr expands to (URI-or-#NULL-NAMESPACE,NCName2) |
An attribute QName consisting only of a local part NCName expands to the null namespace and the local part.
|
statEnv |- NCName of attr expands to (#NULL-NAMESPACE,NCName) |
A variable QName consisting of a prefix NCName and a local part NCName expands to the URI that corresponds to the prefix and the local part.
statEnv.namespace(NCName1) = URI |
|
statEnv |- NCName1:NCName2of var expands to (URI,NCName2) |
A variable QName consisting only of a local part NCName expands to the null namespace and the local part.
|
statEnv |- NCName of var expands to (#NULL-NAMESPACE,NCName) |
A function QName consisting of a prefix NCName and a local part NCName expands to the URI that corresponds to the prefix and the local part.
statEnv.namespace(NCName1) = URI |
|
statEnv |- NCName1:NCName2 of func expands to (URI,NCName2) |
A function QName consisting only of a local part NCName expands to the default function namespace URI and the local part.
statEnv.default_function_namespace = URI |
|
statEnv |- NCName of func expands to (URI,NCName) |
The environment group dynEnv denotes the group of environments built and used during dynamic evaluation.
If evaluation of an expression relies on some component of the dynamic context that has not been assigned a value, a dynamic error is raised. This constraint is formalized in [3.3 Error Handling].
The following environments are part of evaluation environment group:
dynEnv.varValue |
|
|||||
dynEnv.funcDefn |
|
|||||
dynEnv.dateTime |
|
|||||
dynEnv.timezone |
|
|||||
dynEnv.docValue |
|
|||||
dynEnv.collectionValue |
|
|||||
dynEnv.defaultCollectionValue |
|
The initial values for the dynamic context are defined in Section C Context ComponentsXQ and Section C Context ComponentsXP and is denoted by dynEnvDefault in the Formal Semantics.
The following Formal Semantics variables represent the context item, context position, and context size properties of the dynamic context:
Built-in Variable | Represents: |
$ fs:dot |
context item |
$ fs:position |
context position |
$ fs:last |
context size |
Variables with the "fs" prefix are reserved for use in the definition of the Formal Semantics. Since there is no namespace URI associated to the "fs" prefix, users cannot refer to those variables directly using a variable expression.
Values of $
fs:position
and $
fs:last
can be obtained by invoking the fn:position
and fn:last
functions, respectively.
This section reviews the processing model for [XPath/XQuery], and defines the main judgments that are used in this specification. The [XPath/XQuery] processing model is defined normatively in Section 2.2 Processing ModelXQ. This section also explains how the main judgments (normalization rules, static type inference, and dynamic evaluation) relate to the phases in that processing model.
The following figure depicts the [XPath/XQuery] processing model
Figure 1: Processing Model Overview
This processing model is not intended to describe an actual implementation, although a naive implementation might be based upon it. It does not prescribe an implementation technique, but any implementation should produce the same results as obtained by following this processing model and applying the rest of the Formal Semantics specification.
Query processing consists of two phases: a static analysis phase and a dynamic evaluation phase. Static analysis is further divided into four sub-phases. Each phase consumes the result of the previous phase and generates output for the next phase. For each processing phase, we point to the relevant notations introduced later in the document.
[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).]
The purpose of the static analysis phase is to detect errors, e.g., syntax errors or type errors, at compile time rather than at run-time. If no error occurs, the result of static analysis could be some compiled form of [expression/query], suitable for execution by a compiled-[expression/query] processor. Static analysis consists of the following sub-phases:
Parsing. (Step SQ1 in Figure 1). The grammar for the [XPath/XQuery] syntax is defined in [XQuery 1.0: A Query Language for XML]. Parsing may generate syntax errors. If no error occurs, an internal operation tree of the parsed query is created.
Static Context Processing. (Steps SQ2, SQ3, and SQ4 in Figure 1). The static semantics of [expression/query] depends on the input static context. The input static context needs to be generated before the [expression/query] can be analysed. In XQuery, the input static context may be defined by the processing environment and by declarations in the Query Prolog (See [5 Modules and Prologs]). In XPath, the input static context is defined by the processing environment. The static context is denoted by statEnv.
Normalization. (Step SQ5 in Figure 1). To simplify the semantics specification, some normalization is performed on the [expression/query]. The [XPath/XQuery] language provides many powerful features that make [expression/query]s simpler to write and use, but are also redundant. For instance, a complex for
expression might be rewritten as a composition of several simple for
expressions. The language composed of these simpler
[expression/query] is called the [XPath/XQuery] Core language and is described by a grammar which is a subset of the XQuery grammar. The grammar of the [XPath/XQuery] Core language is given in [A Normalized core grammar].
During the normalization phase, each [XPath/XQuery] [expression/query] is mapped into its equivalent [expression/query] in the Core. (Note that this has nothing to do with Unicode Normalization, which works on character strings.) Normalization works by bottom-up application of normalization rules over expressions, starting with normalization of literal expressions and variables.
Specifically the normalization phase is defined in terms of the static part of the context (statEnv) and a [expression/query] (Expr) abstract syntax tree. Formal notations for the normalization phase are introduced in [3.2.2 Normalization judgment].
After normalization, the full semantics is obtained by giving a semantics to the normalized Core [expression/query]. This is done during the last two phases.
Static type analysis. (Step SQ6 in Figure 1). Static type analysis is optional. If this phase is not supported, then normalization is followed directly by dynamic evaluation.
Static type analysis checks whether each [expression/query] is type safe, and if so, determines its static type. Static type analysis is defined only for Core [expression/query]. Static type analysis works by bottom-up application of type inference rules over expressions, taking the type of literals and of input documents into account.
If the [expression/query] is not type-safe, static type analysis yields a type error. For instance, a comparison between an integer value and a string value might be detected as an type error during the static type analysis. If static type analysis succeeds, it yields an abstract syntax tree where each sub-expression is associated with its static type.
More precisely, the static analysis phase is defined in terms of the static context (statEnv) and a Core [expression/query] (CoreExpr). Formal notations for the static analysis phase are introduced in [3.2.3 Static typing judgment].
Static typing does not imply that the content of XML documents must be rigidly fixed or even known in advance. The [XPath/XQuery] type system accommodates "flexible" types, such as elements that can contain any content. Schema-less documents are handled in [XPath/XQuery] by associating a standard type with the document, such that it may include any legal XML content.
If the static analysis phase succeeds, the dynamic evaluation phase (sometimes also called "execution") evaluates a query on input document(s).
Dynamic Context Processing. (Steps DQ2 and DQ3 in Figure 1).The dynamic semantics of [expression/query] depends on the dynamic input context. The dynamic input context needs to be generated before the [expression/query] can be evaluated. The dynamic input context may be defined by the processing environment and by statements in the Query Prolog (See [5 Modules and Prologs]). In XPath, the dynamic input context is defined by the processing environment. The static input context is denoted by dynEnv.
Dynamic Evaluation. (Steps DQ4 and DQ5 in Figure 1). This phase computes the value of an [expression/query]. The semantics of evaluation is defined only for Core [expression/query] terms. The formal description of evaluation works by bottom-up application of evaluation rules over expressions, starting with evaluation of literals and variables. (Note that in practice some implementations may prefer top-down evaluation strategies.) Evaluation may result in a value OR a dynamic error, which may be a non-type error or a type error. If static typing of an expression does not raise a type error, then dynamic evaluation of the same expression will not raise a type error (and thus dynamic type checking can be avoided when static typing is enabled). Dynamic evaluation may still raise a non-type error.
The dynamic evaluation phase is defined in terms of the static context (statEnv) and evaluation context (dynEnv), and a Core [expression/query] (CoreExpr). Formal notations for the dynamic evaluation phase are introduced in [3.2.4 Dynamic evaluation judgment].
Static type analysis catches only certain classes of errors. For instance, it can detect a comparison operation applied between incompatible types (e.g., xs:int
and xs:date
). Some other classes of errors cannot be detected by the static analysis and are only detected at evaluation time. For instance, whether an arithmetic expression on 32 bits integers (xs:int
) yields an out-of-bound value can only be detected at run-time by looking at the data.
While implementations are free to implement different processing models, the [XPath/XQuery] static semantics relies on the existence of a static type analysis phase that precedes any access to the input data.
The above processing phases are all internal to the [XPath/XQuery] processor. They do not deal with how the [XPath/XQuery] processor interacts with the outside world, notably how it accesses actual documents and types. A typical [expression/query] engine would support at least three other important processing phases:
Schema Import Processing. The [XPath/XQuery] type system is based on XML Schema. In order to perform dynamic or static typing, the [XPath/XQuery] processor needs to build type descriptions that correspond to the schema(s) of the input documents. This phase is achieved by mapping all schemas required by the [expression/query] into the [XPath/XQuery] type system. The XML Schema import phase is described in [C Importing Schemas].
Data Model Generation. Expressions are evaluated on values in the [Data Model]. XML documents must be loaded into the [Data Model] before the evaluation phase. This is described in the [Data Model] and is not discussed further here.
Serialization. Once the [expression/query] is evaluated, processors might want to serialize the result of the [expression/query] as actual XML documents. Serialization of data model instances is described in [Data Model Serialization] and is not discussed further here.
The parsing phase is not specified formally; the formal semantics does not define a formal model for the syntax trees, but uses the [XPath/XQuery] concrete syntax directly. More details about parsing for XQuery 1.0 can be found in the [XQuery 1.0: A Query Language for XML] document and more details about parsing for XPath 2.0 can be found in the [XML Path Language (XPath) 2.0] document. No further discussion of parsing is included here.
Normalization is specified using mapping rules, which describe how a [XPath/XQuery] expression is rewritten into an expression in the [XPath/XQuery] Core. Mapping rules are also used in [C Importing Schemas] to specify how XML Schemas are imported into the [XPath/XQuery] type system.
Notation
Mapping rules are written using a square bracket notation, as follows:
[Object]Subscript |
== |
Mapped Object |
The original "object" is written above the == sign. The rewritten "object" is written beneath the == sign. The subscript is used to indicate what kind of "object" is mapped, and sometimes to pass some information between mapping rules.
Since normalization is always applied in the presence of a static context, the above rule is a shorthand for:
The static environment is used in certain normalization rules (e.g. for normalization of function calls). To keep the notation simpler, the static environment is not written in the normalization rules, but it is assumed to be available.
The normalization rule that is used to map "top-level" expressions in the [XPath/XQuery] syntax into expressions in the [XPath/XQuery] Core is:
[Expr]Expr |
== |
CoreExpr |
which indicates that the expression Expr is normalized to the expression CoreExpr in the [XPath/XQuery] Core (with the implied statEnv).
Example
For instance, the following [expression/query]
for $i in (1, 2), $j in (3, 4) return element pair { ($i,$j) }
is normalized to the Core expression
for $i in (1, 2) return for $j in (3, 4) return element pair { ($i,$j) }
in which the "FWLR" expression is mapped into a composition of two simpler "for" expressions.
The static semantics is specified using type inference rules, which relate [XPath/XQuery] expressions to types and specify under what conditions an expression is well typed.
Notation
The judgment
holds when, in the static environment statEnv, the expression Expr has type Type.
Example
The result of static type inference is to associate a static type with every [expression/query], such that any evaluation of that [expression/query] is guaranteed to yield a value that belongs to that type.
For instance, the following expression.
let $v := 3 return $v+5
has type xs:integer
. This can be inferred as follows: the input literals '3' and '5' have type integer, so the variable $v also has type integer. Since the sum of two integers is an integer, the complete expression has type integer.
Note
The type of an expression is computed by inference. Static type inference rules define for each kind of expression how to compute the type of the expression given the types of its sub-expressions. Here is a simple example:
statEnv |- Expr1 : xs:boolean statEnv |- Expr2 : Type2 statEnv |- Expr3 : Type3 |
|
statEnv |- if Expr1 then Expr2 else Expr3 : ( Type2 | Type3 ) |
This rule states that if the conditional expression of an "if" expression has type boolean, then the type of the entire expression is one of the two types of its "then" and "else" clauses. Note that the resulting type is represented as a union: '(Type2|Type3)'.
The "left half" (the part before the :) of the expression below the line corresponds to some [expression/query], for which a type is computed. If the [expression/query] has been parsed into an internal abstract syntax tree, this usually corresponds to some node in that tree. The expression usually has patterns in it (here Expr1, Expr2, and Expr3) that need to be matched against the children of the node in the abstract syntax tree. The expressions above the line indicate things that need to be computed to use this rule; in this case, the types of the condition expression and the two branches of the if-then-else expression. Once those types are computed (by further applying static inference rules recursively to the expressions on each side), then the type of the expression below the line can be computed. This example illustrates a general feature of the [XPath/XQuery] type system: the type of an expression depends only on the type of its sub-expressions. The overall static type inference algorithm is recursive, following the abstract syntax of the [expression/query]. At each point in the recursion, an appropriate matching inference rule is sought; if at any point there is no applicable rule, then static type inference has failed and the [expression/query] is not type correct.
The dynamic, or operational, semantics is specified using value inference rules, which relate [XPath/XQuery] expressions to values, and in some cases specify the order in which an [XPath/XQuery] expression is evaluated.
Notation
The judgment
holds when, in the static environment statEnv and dynamic environment dynEnv, the expression Expr yields the value Value.
The judgment
holds when, in the static environment statEnv and dynamic environment dynEnv, the expression Expr raises the error Error.
The static environment is used in certain cases (e.g. for type matching) during evaluation. To keep the notation simpler, the static environment is not written in the dynamic inference rules, but it is assumed to be available.
Example
For instance, the following expression.
let $v := 3 return $v+5
yields the integer value 8. This can be inferred as follows: the input literals '3' and '5' denote the values 3 and 5, respectively, so the variable $v has the value 3. Since the sum of 3 and 5 is 8, the complete expression has the value 8.
Note
As with static type inference, logical inference rules are used to determine the value of each expression, given the dynamic environment and the values of its sub-expressions.
The inference rules used for dynamic evaluation, like those for static type inference, follow a bottom-up recursive structure, computing the value of expressions from the values of their sub-expressions.
Expressions can raise errors during static analysis or dynamic evaluation. The [Functions and Operators] [XQuery 1.0: A Query Language for XML], and [XML Path Language (XPath) 2.0] specify the conditions under which an expression or operator raises an error. The user may raise an error explicitly by calling the fn:error
function, which takes an optional item as an argument.
Notation
The symbol Error denotes any error. We distinguish between a static errorXQ (denoted by statError), a type errorXQ (denoted by typeError), and a generic dynamic errorXQ (denoted by dynError), which represents all dynamic errors. A static error is raised during static analysis. A type error may be raised during static analysis or dynamic evaluation. A dynamic error is raised during dynamic evaluation. Non-type static errors are not formalized in this document.
Note:
We use a generic dynamic error. The [Functions and Operators] and [XQuery 1.0: A Query Language for XML] documents raise specific error conditions, but because these error conditions can be implemented in any way, we do not formalize them here.
The errors defined in this specification are identified by QNames that have the form err:XXYYnnnn, as described in [XQuery 1.0: A Query Language for XML].
In general, when an error is raised during evaluation of some expression Expr, the error is propogated to the expression Expr1 in which Expr is evaluated. The expression Expr1, in turn, propogates the error to the expression in which Expr1 is evaluated, and so on, until the error is returned to the query environment.
Since most expressions propogate errors as described, we use one inference rule to specify this default behavior. The rule below states that if any sub-expression Expri of expression Expr raises an error dynError then Expr also raises dynError.
There are several expressions, such as [4.6 Logical Expressions] and [4.11 Quantified Expressions], that do not necessarily propogate an error raised by some sub-expression. For each such expression, we give specific error inference rules.
In [XPath/XQuery], the detection and reporting of dynamic errors is implementation dependent. This permits different implementations to choose to evaluate or optimize an expression in different ways. 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, if the variable bound by a let expression is never used in the corresponding return expression, the implementation is not required to evaluate the expression to which the variable is bound.
For simplicity, the dynamic inference rules in Formal Semantics define an eager evaluation semantics for all expressions, i.e., all sub-expressions are evaluated regardless of whether their values are necessary to evaluate the containing expression. For example, every function parameter is evaluated before the body of the function is evaluated, and the expression bound to a let variable is always evaluated. The dynamic semantics rules in the Formal Semantics do not formalize the more flexible evaluation strategy above.
For example, in the following expression, the dynamic semantics rules of the Formal Semantics would raise a dynamic error because a path expression may not be applied to an atomic value. An implementation, however, may not raise an error, because the path expression is not necessary to evaluate the containing let expression.
let $x := 1/foobar return 1
However, the static semantic rules, by definition, are conservative, and as a consequence, a static type error would be raised in our example, even though the sub-expression 1/foobar
may not be evaluated.
[XPath/XQuery] is most generally used to process documents. The representation of a document is normatively defined in [Data Model]. The functions used to access documents and collections are normatively defined in [Functions and Operators].
Document order is defined in [Data Model].
Atomization converts an item sequence into a sequence of atomic values and is implemented by the fn:data
function. Atomization is applied in contexts where an arbitrary sequence of items is used where a sequence of atomic values is expected.
If a sequence of items is encountered where a boolean value is expected, the item sequence's effective boolean value is used. The fn:boolean
function returns the effective boolean value of an item sequence.
[XPath/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 dynamic semantics of these three input functions are described in more detail in [Functions and Operators].
In certain places in the XQuery grammar, a statically known valid absolute URI is required. Those cases are treated as described in [XQuery 1.0: A Query Language for XML]
All the built-in types of XML Schema are recognized by [XPath/XQuery]. In addition, [XPath/XQuery] recognizes the predefined types xdt:anyAtomicType
, xdt:untypedAtomic
and xdt:untyped
and the duration subtypes xdt:yearMonthDuration
and xdt:dayTimeDuration
. The definition of
those types in the [XPath/XQuery] type system is given below.
[Definition: The following type definition of xs:anyType
reflects the semantics of the Ur type from Schema in the [XPath/XQuery] type system.]
define type xs:anyType restricts xs:anyType { attribute*, ( xdt:anyAtomicType* | ( element | text | comment | processing-instruction )* ) }
[Definition: The following type definition of xs:anySimpleType
reflects the semantics of the Ur simple type from Schema in the [XPath/XQuery] type system.]
define type xs:anySimpleType restricts xs:anyType { xdt:anyAtomicType* }
The name of the Ur simple type is xs:anySimpleType
. It is derived by restriction from xs:anyType
, its content is a sequence any atomic types.
[Definition: The following type definition of xdt:anyAtomicType
reflects the semantics of xdt:anyAtomicType
in the [XPath/XQuery] type system.]
define type xdt:anyAtomicType restricts xs:anySimpleType { ( xs:string | xs:boolean | xs:decimal | xs:float | xs:double | xs:duration | xs:dateTime | xs:time | xs:date | xs:gYearMonth | xs:gYear | xs:gMonthDay | xs:gDay | xs:gMonth | xs:hexBinary | xs:base64Binary | xs:anyURI | xs:QName | xs:NOTATION | xdt:untypedAtomic ) }
[Definition: The following type definitions of the XML Schema primitive types reflects the semantics of the primitive types from Schema in the [XPath/XQuery] type system.]
define type xs:string restricts xdt:anyAtomicType define type xs:boolean restricts xdt:anyAtomicType define type xs:decimal restricts xdt:anyAtomicType define type xs:float restricts xdt:anyAtomicType define type xs:double restricts xdt:anyAtomicType define type xs:duration restricts xdt:anyAtomicType define type xs:dateTime restricts xdt:anyAtomicType define type xs:time restricts xdt:anyAtomicType define type xs:date restricts xdt:anyAtomicType define type xs:gYearMonth restricts xdt:anyAtomicType define type xs:gYear restricts xdt:anyAtomicType define type xs:gMonthDay restricts xdt:anyAtomicType define type xs:gDay restricts xdt:anyAtomicType define type xs:gMonth restricts xdt:anyAtomicType define type xs:hexBinary restricts xdt:anyAtomicType define type xs:base64Binary restricts xdt:anyAtomicType define type xs:anyURI restricts xdt:anyAtomicType define type xs:QName restricts xdt:anyAtomicType define type xs:NOTATION restricts xdt:anyAtomicType
All of those primitive types derive from xdt:anyAtomicType
. Note that the value space of each atomic type (such as xs:string
) does not appear. The value space for each type is built-in and is as defined in [Schema Part 2].
[Definition: The type xdt:untypedAtomic
is defined as follows.]
define type xdt:untypedAtomic restricts xdt:anyAtomicType
Note that this rule does not indicate the value space of xdt:untypedAtomic
. By definition, xdt:untypedAtomic
has the same value space as xs:string
.
The following example shows two atomic values. The first one is a value of type string containing "Database". The second one is an untyped atomic value containing "Database".
"Databases" of type xs:string "Databases" of type xdt:untypedAtomic
[Definition: The type xdt:untyped
is defined as follows.]
define type xdt:untyped restricts xs:anyType { attribute of type xdt:untypedAtomic*, ( element of type xdt:untyped | text | comment | processing-instruction? )* }
[Definition: The following type definitions of the XML Schema derived types reflects the semantics of the XML Schema types derived by restriction from another atomic type.]
define type xs:normalizedString restricts xs:string define type xs:token restricts xs:normalizedString define type xs:language restricts xs:token define type xs:NMTOKEN restricts xs:token define type xs:Name restricts xs:token define type xs:NCName restricts xs:Name define type xs:ID restricts xs:Name define type xs:IDREF restricts xs:Name define type xs:ENTITY restricts xs:Name define type xs:integer restricts xs:decimal define type xs:nonPositiveInteger restricts xs:integer define type xs:negativeInteger restricts xs:nonPositiveInteger define type xs:long restricts xs:integer define type xs:int restricts xs:long define type xs:short restricts xs:int define type xs:byte restricts xs:short define type xs:nonNegativeInteger restricts xs:integer define type xs:unsignedLong restricts xs:nonNegativeInteger define type xs:unsignedInt restricts xs:unsignedLong define type xs:unsignedShort restricts xs:unsignedInt define type xs:unsignedByte restricts xs:unsignedShort define type xs:positiveInteger restricts xs:nonNegativeInteger
Three XML Schema built-in derived types are derived by list, as follows. Note that those derive directly from xs:anySimpleType
, since they are derived by list, and that their value space is defined using a "one or more" occurrence indicator.
define type xs:NMTOKENS restricts xs:anySimpleType { xs:NMTOKEN+ } define type xs:IDREFS restricts xs:anySimpleType { xs:IDREF+ } define type xs:ENTITIES restricts xs:anySimpleType { xs:ENTITY+ }
For example, here is an element whose content is of type xs:IDREFS
.
element a of type xs:IDREFS { "id1" of type xs:IDREF, "id2" of type xs:IDREF, "id3" of type xs:IDREF }
Note that the type name xs:IDREFS
derives from xs:anySimpleType
, but not from xs:IDREF
. As a consequence, calling the following three XQuery functions with the element a
as a parameter succeeds for f1
and f2
, but raises a type error for f3
.
declare function f1($x as element(*,xs:anySimpleType)) { $x } declare function f2($x as element(*,xs:IDREFS)) { $x } declare function f3($x as element(*,xs:IDREF)) { $x }
[Definition: The totally ordered duration types, xdt:yearMonthDuration
and xdt:dayTimeDuration
, are derived by restriction from xs:duration
.]
define type xdt:yearMonthDuration restricts xs:duration define type xdt:dayTimeDuration restricts xs:duration
[Definition: In addition, the Formal Semantics uses the additional type fs:numeric
. This type is necessary for the specification of some of XPath type conversion rules. It is defined as follows.]
define type fs:numeric restricts xs:anyAtomicType { xs:decimal | xs:float | xs:double }
The typed value of a node is computed by the fn:data
function, and the string value of a node is computed by the fn:string
function, defined in [Functions and Operators]. The normative definitions of typed value and string value are defined in [Data Model].
Introduction
Sequence types can be used in [XPath/XQuery] to refer to an XML Schema type. Sequence types are used to declare the types of function parameters and in several [XPath/XQuery] expressions.
The syntax of sequence types is described by the following grammar productions.
[117 (XQuery)] | SequenceType |
::= | (ItemType OccurrenceIndicator?) |
[119 (XQuery)] | ItemType |
::= | AtomicType | KindTest | ("item" "(" ")") |
[118 (XQuery)] | OccurrenceIndicator |
::= | "?" | "*" | "+" |
[120 (XQuery)] | AtomicType |
::= | QName |
[121 (XQuery)] | KindTest |
::= | DocumentTest |
[123 (XQuery)] | DocumentTest |
::= | "document-node" "(" (ElementTest | SchemaElementTest)? ")" |
[131 (XQuery)] | ElementTest |
::= | "element" "(" (ElementNameOrWildcard ("," TypeName "?"?)?)? ")" |
[133 (XQuery)] | SchemaElementTest |
::= | "schema-element" "(" ElementDeclaration ")" |
[134 (XQuery)] | ElementDeclaration |
::= | ElementName |
[127 (XQuery)] | AttributeTest |
::= | "attribute" "(" (AttribNameOrWildcard ("," TypeName)?)? ")" |
[129 (XQuery)] | SchemaAttributeTest |
::= | "schema-attribute" "(" AttributeDeclaration ")" |
[130 (XQuery)] | AttributeDeclaration |
::= | AttributeName |
[132 (XQuery)] | ElementNameOrWildcard |
::= | ElementName | "*" |
[136 (XQuery)] | ElementName |
::= | QName |
[128 (XQuery)] | AttribNameOrWildcard |
::= | AttributeName | "*" |
[135 (XQuery)] | AttributeName |
::= | QName |
[137 (XQuery)] | TypeName |
::= | QName |
[126 (XQuery)] | PITest |
::= | "processing-instruction" "(" (NCName | StringLiteral)? ")" |
[125 (XQuery)] | CommentTest |
::= | "comment" "(" ")" |
[124 (XQuery)] | TextTest |
::= | "text" "(" ")" |
[122 (XQuery)] | AnyKindTest |
::= | "node" "(" ")" |
Core Grammar
The Core grammar productions for sequence types are:
[80 (Core)] | SequenceType |
::= | (ItemType OccurrenceIndicator?) |
[82 (Core)] | ItemType |
::= | AtomicType | KindTest | ("item" "(" ")") |
[81 (Core)] | OccurrenceIndicator |
::= | "?" | "*" | "+" |
[83 (Core)] | AtomicType |
::= | QName |
[84 (Core)] | KindTest |
::= | DocumentTest |
[86 (Core)] | DocumentTest |
::= | "document-node" "(" (ElementTest | SchemaElementTest)? ")" |
[94 (Core)] | ElementTest |
::= | "element" "(" (ElementNameOrWildcard ("," TypeName "?"?)?)? ")" |
[96 (Core)] | SchemaElementTest |
::= | "schema-element" "(" ElementDeclaration ")" |
[97 (Core)] | ElementDeclaration |
::= | ElementName |
[90 (Core)] | AttributeTest |
::= | "attribute" "(" (AttribNameOrWildcard ("," TypeName)?)? ")" |
[92 (Core)] | SchemaAttributeTest |
::= | "schema-attribute" "(" AttributeDeclaration ")" |
[93 (Core)] | AttributeDeclaration |
::= | AttributeName |
[95 (Core)] | ElementNameOrWildcard |
::= | ElementName | "*" |
[99 (Core)] | ElementName |
::= | QName |
[91 (Core)] | AttribNameOrWildcard |
::= | AttributeName | "*" |
[98 (Core)] | AttributeName |
::= | QName |
[100 (Core)] | TypeName |
::= | QName |
[89 (Core)] | PITest |
::= | "processing-instruction" "(" (NCName | StringLiteral)? ")" |
[88 (Core)] | CommentTest |
::= | "comment" "(" ")" |
[87 (Core)] | TextTest |
::= | "text" "(" ")" |
[85 (Core)] | AnyKindTest |
::= | "node" "(" ")" |
The semantics of SequenceTypes is defined by means of normalization rules from SequenceTypes into types in the [XPath/XQuery] type system (See [2.4 The [XPath/XQuery] Type System]).
However, the [XPath/XQuery] type system not being part of the [XPath/XQuery] syntax, the SequenceType syntax is still part of the [XPath/XQuery] Core. Normalization from SequenceTypes to types is not applied during the normalization phase but whenever a dynamic or static rule requires it. Normalization of SequenceTypes is the only example of normalization that does not yield an expression in the [XPath/XQuery] Core and that occurs on-demand in dynamic or static rules.
Introduction
During processing of a query, it is sometimes necessary to determine whether a given value matches a type that was declared using the SequenceType syntax. This process is known as SequenceType matching, and is formally specified in [8.3 Judgments for type matching].
Notation
To define normalization of SequenceTypes to the [XPath/XQuery] type system, the following auxiliary mapping rule is used.
[SequenceType]sequencetype |
== |
Type |
specifies that SequenceType is mapped to a Type, in the [XPath/XQuery] type system.
OccurenceIndicators are left unchanged when normalizing SequenceTypes into [XPath/XQuery] types. Each kind of SequenceType component is normalized separately into the [XPath/XQuery] type system.
[ItemType OccurrenceIndicator]sequencetype |
== |
[ItemType]sequencetype OccurrenceIndicator |
The "void()" sequence type is mapped to the empty type.
[void()]sequencetype |
== |
empty |
An atomic type is normalized to itself in the [XPath/XQuery] type system.
An "element" SequenceType without content or with a wildcard and no type name is normalized into a wildcard element type.
[element()]sequencetype |
== |
element |
[element(*)]sequencetype |
== |
element |
An "element" SequenceType with a wildcard and a type name is normalized into a wildcard element type with a corresponding type name. The presence of a "?" after the type name indicates a nillable element.
[element(*,TypeName)]sequencetype |
== |
element of type TypeName |
[element(*,TypeName?)]sequencetype |
== |
element nillable of type TypeName |
An "element" SequenceType with a name and a type name is normalized into an element type with a corresponding type name. The presence of a "?" after the type name indicates a nillable element.
[element(ElementName,TypeName)]sequencetype |
== |
element ElementName of type TypeName |
[element(ElementName,TypeName?)]sequencetype |
== |
element ElementName nillable of type TypeName |
An "element" SequenceType with only a name is normalized into a nillable element type with a corresponding name. The reason for the normalization to allow nillable elements is because the semantics of SequenceTypes in that case allows it to match every possible element with that names, regardless of its type or nilled property.
[element(ElementName)]sequencetype |
== |
element ElementName nillable of type xs:anyType |
A "schema-element" SequenceType with an element declaration is normalized into a reference to the corresponding global element declaration.
[schema-element(ElementName)]sequencetype |
== |
element ElementName |
An "attribute" SequenceType without content or with a wildcard and no type name is normalized into a wildcard attribute type.
[attribute()]sequencetype |
== |
attribute |
[attribute(*)]sequencetype |
== |
attribute |
An "attribute" SequenceType with a wildcard and a type name is normalized into a wildcard attribute type with a corresponding type name.
[attribute(*,TypeName)]sequencetype |
== |
attribute of type TypeName |
An "attribute" SequenceType with a name and a type name is normalized into an attribute type with a corresponding type name.
[attribute(AttributeName,TypeName)]sequencetype |
== |
attribute AttributeName of type TypeName |
A "schema-attribute" SequenceType with an attribute declaration is normalized into a reference to the corresponding global attribute declaration.
[schema-attribute(AttributeName)]sequencetype |
== |
attribute AttributeName |
A "document-node()" sequence types is normalized into the corresponding document type.
[document-node()]sequencetype |
== |
document |
A "document-node" sequence type with an element test (resp. a schema element test) is normalized into the corresponding document type, whose content is the normalization of the element test (resp. schema element test), interleaved with an arbitrary sequence of processing instruction, comment, and text nodes.
[document-node(ElementTest)]sequencetype |
== |
document { [ElementTest]sequencetype & ( processing-instruction | comment ) *} |
[document-node(SchemaElementTest)]sequencetype |
== |
document { [SchemaElementTest]sequencetype & ( processing-instruction | comment ) *} |
A "processing-instruction()" SequenceType is normalized into the corresponding processing-instruction type.
[processing-instruction()]sequencetype |
== |
processing-instruction |
The [XPath/XQuery] type system does not model the target of a processing-instruction, which is treated as a dynamic property. Therefore a "processing-instruction" SequenceType with a string or NCName parameter is normalized into an optional processing-instruction type.
[processing-instruction(StringLiteral)]sequencetype |
== |
processing-instruction? |
[processing-instruction(NCName)]sequencetype |
== |
processing-instruction? |
A "comment()" SequenceType is normalized into the corresponding comment type.
[comment()]sequencetype |
== |
comment |
A "text()" SequenceType is normalized into the corresponding text type.
[text()]sequencetype |
== |
text |
The "node()" SequenceType denotes any node. It is normalized into a choice between the corresponding wildcard types for each kind of node.
[node()]sequencetype |
== |
(element | attribute | text | document | comment | processing-instruction) |
The "item()" SequenceType denotes any node or atomic value. It is normalized into a choice between the corresponding wildcard types for each kind of nodes or atomic values.
[item()]sequencetype |
== |
(element | attribute | text | document | comment | processing-instruction | xdt:anyAtomicType ) |
[154 (XQuery)] | Comment |
::= | "(:" (CommentContents | Comment)* ":)" |
[155 (XQuery)] | CommentContents |
::= | (Char+ - (Char* ':)' Char*)) |
Comments are lexical constructs only, and have no effect on the meaning of the query, and therefore do not have any formal semantics.
This section gives the semantics of all the [XPath/XQuery] expressions. The organization of this section parallels the organization of Section 3 ExpressionsXQ.
[31 (XQuery)] | Expr |
::= | ExprSingle ("," ExprSingle)* |
[32 (XQuery)] | ExprSingle |
::= | FLWORExpr |
[1 (XPath)] | XPath |
::= | Expr |
For each expression, a short description and the relevant grammar productions are given. The semantics of an expression includes the normalization, static analysis, and dynamic evaluation phases. Recall that normalization rules translate [XPath/XQuery] syntax into Core syntax. In the sections that contain normalization rules, the Core grammar productions into which the expression is normalized are also provided. After normalization, sections on static type inference and dynamic evaluation define the static type and dynamic value for the Core expression.
Core Grammar
The Core grammar productions for expressions are:
[30 (Core)] | Expr |
::= | ExprSingle ("," ExprSingle)* |
[31 (Core)] | ExprSingle |
::= | FLWORExpr |
It is a static type error for any expression to have the empty type, except for the following expressions and functions:
Empty parenthesis ()
, which denote the empty sequence.
The fn:data
function and all functions in the fs namespace applied to empty parenthesis()
.
Any function which returns the empty type.
The reason for those exception is that they are typically part of the result of normalizing a larger user-level expression and are used to capture the semantics of the user-level expression when applied to the empty sequence.
The rule below enforces the above constraints. The static typing rule for ()
is in [4.1.3 Parenthesized Expressions].
|
||||
|
||||
|
The rule is written in this way (i.e., in the double negative), because for any expression such that no static type rule applies to the expression, a static type error is raised. That is, the absence of an applicable static rule indicates an error. For example, if an expression is not an empth parenthesis ()
but has the empty type, the above rule does not apply and therefore a static error is raised.
Example
The above rule can catch common mistakes, such as the misspelling of an element or attribute name or referencing of an element or attribute that does not exist. For instance, the following path expression
$x/title
raises a static error if the type of variable $x
does not include any title
children elements.
Primary expressions are the basic primitives of the language.They include literals, variables, function calls, and the parenthesized expressions.
[83 (XQuery)] | PrimaryExpr |
::= | Literal | VarRef | ParenthesizedExpr | ContextItemExpr | FunctionCall | Constructor | OrderedExpr | UnorderedExpr |
Core Grammar
The Core grammar production for primary expressions is:
[62 (Core)] | PrimaryExpr |
::= | Literal | VarRef | ParenthesizedExpr | FunctionCall |
Introduction
A literal is a direct syntactic representation of an atomic value. [XPath/XQuery] supports two kinds of literals: string literals and numeric literals.
[84 (XQuery)] | Literal |
::= | NumericLiteral | StringLiteral |
[85 (XQuery)] | NumericLiteral |
::= | IntegerLiteral | DecimalLiteral | DoubleLiteral |
[138 (XQuery)] | IntegerLiteral |
::= | Digits |
[139 (XQuery)] | DecimalLiteral |
::= | ("." Digits) | (Digits "." [0-9]*) |
[140 (XQuery)] | DoubleLiteral |
::= | (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits |
[142 (XQuery)] | StringLiteral |
::= | ('"' (PredefinedEntityRef | CharRef | ('"' '"') | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | ("'" "'") | [^'&])* "'") |
[147 (XQuery)] | PredefinedEntityRef |
::= | "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" |
[146 (XQuery)] | Digits |
::= | [0-9]+ |
Core Grammar
The Core grammar productions for literals are:
[63 (Core)] | Literal |
::= | NumericLiteral | StringLiteral |
[64 (Core)] | NumericLiteral |
::= | IntegerLiteral | DecimalLiteral | DoubleLiteral |
[101 (Core)] | IntegerLiteral |
::= | Digits |
[102 (Core)] | DecimalLiteral |
::= | ("." Digits) | (Digits "." [0-9]*) |
[103 (Core)] | DoubleLiteral |
::= | (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits |
[105 (Core)] | StringLiteral |
::= | ('"' (('"' '"') | [^"])* '"') | ("'" (("'" "'") | [^'])* "'") |
[110 (Core)] | PredefinedEntityRef |
::= | "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" |
[109 (Core)] | Digits |
::= | [0-9]+ |
All literals are Core expressions, therefore no normalization rules are required for literals. Predefined entity references and character references in strings are resolved to characters as part of parsing and therefore they do not occur in the Core grammar.
In the static semantics, the type of an integer literal is simply xs:integer:
In the dynamic semantics, an integer literal is evaluated by constructing an atomic value in the data model, which consists of the literal value and its type:
The formal definitions of decimal, double, and string literals are analogous to those for integer.
Literal expressions never raise a dynamic error. Note that literal overflows are raised during parsing.
Introduction
A variable evaluates to the value to which the variable's QName is bound in the dynamic context.
[86 (XQuery)] | VarRef |
::= | "$" VarName |
[144 (XQuery)] | VarName |
::= | QName |
Core Grammar
The Core grammar productions for variable references are:
[65 (Core)] | VarRef |
::= | "$" VarName |
[107 (Core)] | VarName |
::= | QName |
A variable is a Core expression, therefore no normalization rule is required for a variable.
In the static semantics, the type of a variable is simply its type in the static type environment statEnv.varType:
|
|||
|
|||
|
If the variable is not bound in the static environment, a static error is raised.
In the dynamic semantics, a locally declared variable is evaluated by "looking up" its value in dynEnv.varValue:
|
|||
|
|||
|
In the dynamic semantics, an imported variable is evaluated in the dynamic context of the module in which it is declared:
|
|||||
|
|||||
|
If the variable is not bound in the dynamic environment, a dynamic error is raised; the default rules in [3.3 Error Handling] cover this error.
[87 (XQuery)] | ParenthesizedExpr |
::= | "(" Expr? ")" |
Core Grammar
The Core grammar production for parenthesized expressions is:
[66 (Core)] | ParenthesizedExpr |
::= | "(" Expr? ")" |
Empty parenthesis ()
always have the empty type. Remember that it is a static error for most expressions other than ()
to have the empty type (see [4 Expressions] for the complete rule.)
Empty parenthesis ()
evaluate to the empty sequence.
The default rules for propogating errors, described in [3.3 Error Handling] apply to parenthesized expressions.
[88 (XQuery)] | ContextItemExpr |
::= | "." |
Introduction
A context item expression evaluates to the context item, which may be either a node or an atomic value.
A context item expression is normalized to the built-in variable $
fs:dot
. Because it can only be bound through the external context or a path expression, there is no need for a specific typing rule to enforce that its value is a singleton item.
Introduction
A function call consists of a QName followed by a parenthesized list of zero or more expressions. In [XPath/XQuery], the actual argument to a function is called an argument and the formal argument of a function is called a parameter. We use the same terminology here.
[91 (XQuery)] | FunctionCall |
::= | QName "(" (ExprSingle ("," ExprSingle)*)? ")" |
Because [XPath/XQuery] implicitly converts the values of function arguments, a normalization step is required.
Notation
Normalization of function calls uses an auxiliary mapping []FunctionArgument(SequenceType) used to insert conversions of function arguments that depend only on the expected SequenceType of the corresponding parameters. It is defined as follows:
[Expr]FunctionArgument(SequenceType) |
== |
[[[Expr]Expr]AtomizeAtomic(SequenceType)]Convert(SequenceType) |
where
[Expr]AtomizeAtomic(SequenceType) denotes
fn:data (Expr) |
If SequenceType <: xdt:anyAtomicType * and Expr : Type and not(Type=empty ) |
|
Expr | Otherwise |
which specifies that if the function expects atomic parameters, then fn:data
is called to obtain them.
[Expr]Convert(SequenceType) denotes
fs:convert-simple-operand (Expr,PrototypicalValue) |
If SequenceType <: xdt:anyAtomicType * |
Expr | Otherwise |
where PrototypicalValue is a built-in atomic value used to encode the corresponding atomic type. A value is used here since [XPath/XQuery] expressions cannot operate directly on types. Which value is chosen does not have any impact on the actual semantics, only its actual atomic type matters.
Note
The fs:convert-simple-operand
function takes a PrototypicalValue, which is a value of the target type, to ensure that conversion to base types is possible even though types are not first class objects in [XPath/XQuery].
Core Grammar
The Core grammar production for function calls is:
[69 (Core)] | FunctionCall |
::= | QName "(" (ExprSingle ("," ExprSingle)*)? ")" |
Each argument expression in a function call is normalized to its corresponding Core expression by applying []FunctionArgument(SequenceType) for each argument with the expected SequenceType for the argument inserted.
[ QName (Expr1, ..., Exprn) ]Expr |
== |
QName ( [Expr1]FunctionArgument(SequenceType1), ..., [Exprn]FunctionArgument(SequenceTypen) ) |
Note that this normalization rule depends on the static environment containing function signatures and is the only normalization rule that depends on statEnv. Furthermore notice that the normalization is only well-defined when it is guaranteed that overloading is restricted to atomic types with the same quantifier. This is presently the case.
To typecheck a Core function call we first check in Section [7 Additional Semantics of Functions] if there is a specialized typing rule for the function, and, if so, use it. Otherwise, the function signatures matching the function name and arity are retrieved from the static environment. The type of each argument to the function must be a subtype of a type that is promotable to the corresponding function parameter type of the function; if the inferred type is a union of atomic types then this check is performed separately for each possibility.
The first rule bootstraps type checking of a function call: It expands the function's QName and then applies the function call rule for the expanded function call:
|
||||||
|
||||||
|
For a function call in which the static type of one of the expressions passed as argument is a union of atomic types, the function call is type checked once separately for each atomic type in that union. The static type of the entire function call expression is then the union of the types computed in each case, as follows:
|
|||||
|
|||||
|
Note
Notice that this semantics makes sense since the type declared for a function parameter, which uses the sequence types syntax, cannot itself be a union.
Finally, the following auxilliary rule type checks a function call in which none of the actual arguments has a type that is a union of atomic types. The rule looks up the function in the static environment and checks that some signature for the function satisfies the following constraint: the type of each actual argument is a subtype of some type that can be promoted to the type of the correponding function parameter. In this case, the function call is well typed and the result type is the return type specified in the function's signature.
|
||||||||||||
|
||||||||||||
|
The function body itself is not analyzed for each invocation: static typing of the function definition itself guarantees that the function body always returns a value of the declared return type.
Notice that the static typing rule checks the function signature in order to determine whether a function exists rather than just the function arity: this is consistent because it will reject function calls with the wrong arity in addition to function calls with the right arity but incompatible parameter types.
Based on a function's name and parameter types, the function body is retrieved from the dynamic environment.
If the function is a locally-declared, user-defined function then it is evaluated as follows. First, the rule evaluates each actual function argument expression. Next, a match is searched for among the function's possible declaration signatures, retrieved from statEnv.funcType. If the function is not present in the environment, or there is no matching declaration signature, a type error is raised. Otherwise, the function body and formal variables are obtained from dynEnv.funcDefn for the matching declaration signature. The rule then extends dynEnv.varValue by binding each formal variable to its corresponding value (converted by the normalization as required for the expected type), and evaluates the body of the function in the new environment. The resulting value is the value of the function call.
|
|||||||||||||
|
|||||||||||||
|
Note that the function body is evaluated in the default (top-level) environment extended with just the parameter bindings. Note also that input values and output values are matched against the types declared for the function. If static analysis was performed, all these checks are guaranteed to be true and may be omitted.
The rule for evaluating an imported function is similar to that for evaluating a locally declared function, except that the function call is evaluated in the dynamic context of the module in which it is declared.
|
|||||||||||||||||
|
|||||||||||||||||
|
If the function is a built-in or external function then the rule is somewhat simpler:
|
|||||||||||||
|
|||||||||||||
|
Calls to built-in or external functions use the following auxiliary judgment to evaluate the built-in or external function:
"The built-in or external function F (from [Data Model], [Functions and Operators], [7 Additional Semantics of Functions], or as defined in dynEnvDefault.funcDefn) applied to the given parameter values yields the specified result value" | ||
|
||
|
If the evaluation of any actual argument raises an error, the function call can raise an error. This rule applies to both user-defined and built-in functions. Note that if more than one expression may raise an error, the function call may raise any one of the errors.
|
|||||
|
|||||
|
If, for all possible function signatures, the evaluation of some actual argument yields a value that cannot be promoted to the corresponding formal type of the parameter, the function call raises a type error. This rule applies to both user-defined and built-in functions.
|
||||||
|
||||||
|
If the evaluation of the function call to a user-defined function yields a value that cannot be promoted to the corresponding return type of the function, the function call raises a type error.
|
|||||||||||||
|
|||||||||||||
|
If the evaluation of the function call to a built-in or external function yields a value that cannot be promoted to the corresponding return type of the function, the built-in or external function call raises a type error.
|
|||||||||||||
|
|||||||||||||
|
Built-in function calls use the following auxiliary judgment to evaluate the built-in function call. If the built-in function raises an error, the function call raises an error.
Introduction
Path expressions are used to locate nodes within a tree. There are two kinds of path expressions, absolute path expressions and relative path expressions. An absolute path expression is a rooted relative path expression. A relative path expression is composed of a sequence of steps.
[67 (XQuery)] | PathExpr |
::= | ("/" RelativePathExpr?) |
[68 (XQuery)] | RelativePathExpr |
::= | StepExpr (("/" | "//") StepExpr)* |
Core Grammar
PathExpr and RelativePathExpr are fully normalized, therefore they have no corresponding productions in the Core. The grammar for path expressions in the Core starts with the StepExpr production.
Absolute path expressions are path expressions starting with the /
or //
symbols, indicating that the expression must be applied on the root node in the current context. The root node in the current context is the greatest ancestor of the context node. The following two rules normalize absolute path expressions to relative ones. They use the fn:root
function, which returns the greatest ancestor of its argument node. The treat expressions guarantee that the value
bound to the context variable $
fs:dot
is a document node.
[/]Expr |
== |
(fn:root (self::node()) treat as document-node()) |
[/ RelativePathExpr]Expr |
== |
[((fn:root (self::node())) treat as document-node()) / RelativePathExpr]Expr |
["//" RelativePathExpr]Expr |
== |
[((fn:root (self::node())) treat as document-node) / descendant-or-self::node() / RelativePathExpr]Expr |
[ StepExpr // RelativePathExpr ]Expr |
== |
[StepExpr / descendant-or-self::node() / RelativePathExpr]Expr |
A composite relative path expression (using /
) is normalized into a for
expression by concatenating the sequences obtained by mapping each node of the left-hand side in document order to the sequence it generates on the right-hand side. The call to the fs:distinct-doc-order
function ensures that the result is in document order without duplicates. The dynamic context is defined by binding the
$
fs:dot
, $
fs:sequence
, $
fs:position
and $
fs:last
variables.
Note that sorting by document order enforces the restriction that input and output sequences contains only nodes, and that the last step in a path expression may actualy return atomic values.
[StepExpr / RelativePathExpr]Expr | |||||||
== | |||||||
|
Note that for this section uses some auxiliary judgments which are defined in [8.2 Judgments for step expressions and filtering].
Introduction
[69 (XQuery)] | StepExpr |
::= | AxisStep | FilterExpr |
[70 (XQuery)] | AxisStep |
::= | (ForwardStep | ReverseStep) PredicateList |
[71 (XQuery)] | ForwardStep |
::= | (ForwardAxis NodeTest) | AbbrevForwardStep |
[74 (XQuery)] | ReverseStep |
::= | (ReverseAxis NodeTest) | AbbrevReverseStep |
[81 (XQuery)] | PredicateList |
::= | Predicate* |
Core Grammar
The Core grammar productions for XPath steps are:
[53 (Core)] | StepExpr |
::= | AxisStep | PrimaryExpr |
[54 (Core)] | AxisStep |
::= | ForwardStep | ReverseStep |
[55 (Core)] | ForwardStep |
::= | ForwardAxis NodeTest |
[57 (Core)] | ReverseStep |
::= | ReverseAxis NodeTest |
Note
Step expressions can be followed by predicates. Normalization of predicates uses the following auxiliary mapping rule: []Predicates, which is specified in [4.2.2 Predicates]. Normalization for step expressions also uses the following auxiliary mapping rule: []Axis, which is specified in [4.2.1.1 Axes].
Normalization of predicates need to distinguish between forward steps, reverse steps, and primary expressions.
As explained in the [XPath/XQuery] document, applying a step in XPath changes the focus (or context). The change of focus is made explicit by the normalization rule below, which binds the variable $
fs:dot
to the node currently being processed, and the variable $
fs:position
to the position (i.e., the position within the input sequence) of that node.
There are two sets of normalization rules for Predicates. The first set of rules apply when the predicate is a numeric literal or the expression last()
. The second set of rules apply to all predicate expressions other than numeric literals and the expression last()
. In the first case, the normalization rules provides a more precise static type than if the general rules were applied.
When the predicate expression is a numeric literal or the fn:last
function, the following normalization rules apply.
[ForwardStep PredicateList "[" Numeric "]"]Expr | ||
== | ||
|
[ForwardStep PredicateList "[" fn:last () "]"]Expr |
|||
== | |||
|
When predicates are applied on a reverse step, the position variable is bound in reverse document order.
[ReverseStep PredicateList "[" Numeric "]"]Expr | ||||
== | ||||
|
When the step is a reverse axis, then the last item in the context sequence is the first in document order.
[ReverseStep PredicateList "[" fn:last () "]"]Expr |
||
== | ||
|
The normalization rules above all use the function fn:subsequence
to select a particular item. The static typing rules for this function are defined in [7.2.13 The fn:subsequence function].
When predicates are applied on a forward step, the input sequence is first sorted in document order and duplicates are removed. The context is changed by binding the $
fs:dot
variable to each node in document order.
[ForwardStep PredicateList "[" Expr "]"]Expr | ||||
== | ||||
|
When predicates are applied on a reverse step, the input sequence is first sorted in document order and duplicates are removed. The context is changed by binding the $
fs:dot
variable to each node in document order.
[ReverseStep PredicateList "[" Expr "]"]Expr | |||||
== | |||||
|
Finally, a stand-alone forward or reverse step is normalized by the auxiliary normalization rule for Axis.
[ForwardStep]Expr |
== |
fs:apply-ordering-mode ([ForwardStep]Axis) |
[ReverseStep]Expr |
== |
fs:apply-ordering-mode ([ReverseStep]Axis) |
The static semantics of an Axis NodeTest pair is obtained by retrieving the type of the context node, and applying the two filters (the Axis, and then the NodeTest with a PrincipalNodeKind) on the result.
|
||||||
|
||||||
statEnv |- Axis NodeTest : Type3 |
Note
Note that the second judgment in the inference rule requires that the context item be a node, guaranteeing that a type error is raised when the context item is an atomic value.
The dynamic semantics of an Axis NodeTest pair is obtained by retrieving the context node, and applying the two filters (Axis, then NodeTest) on the result. The application of each filter is expressed through the filter judgment as follows.
|
||||||
|
||||||
dynEnv |- Axis NodeTest => fs:distinct-doc-order (Value3) |
Note
Note that the second judgment in the inference rule guarantees that the context item is bound to a node.
If the context item is not a node, the evaluation of an axis node test expression raises a dynamic error.
Introduction
The XQuery grammar for forward and reverse axis is as follows.
[72 (XQuery)] | ForwardAxis |
::= | ("child" "::") |
[75 (XQuery)] | ReverseAxis |
::= | ("parent" "::") |
In the case of XPath, forward axis also contain the namespace::
axis.
[30 (XPath)] | ForwardAxis |
::= | ("child" "::") |
Core Grammar
The Core grammar productions for XPath axis are:
[56 (Core)] | ForwardAxis |
::= | ("child" "::") |
[58 (Core)] | ReverseAxis |
::= | ("parent" "::") |
Notation
Normalization of axis uses the following auxiliary mapping rule: []Axis.
Normalization for all axis is specified as follows.
The semantics of the following(-sibling) and preceding(-sibling) axes are expressed by mapping them to Core expressions, all other axes are part of the Core and therefore are left unchanged through normalization.
[following-sibling:: NodeTest]Axis |
== |
[let $e := . in $e/parent::node()/child:: NodeTest [.>>$e]]Expr |
[following:: NodeTest]Axis |
== |
[ancestor-or-self::node()/following-sibling::node()/descendant-or-self:: NodeTest]Expr |
All other forward axes are part of the Core [XPath/XQuery] and handled by the normalization rules below:
[child:: NodeTest]Axis |
== |
child:: NodeTest |
[attribute:: NodeTest]Axis |
== |
attribute:: NodeTest |
[self:: NodeTest]Axis |
== |
self:: NodeTest |
[descendant:: NodeTest]Axis |
== |
descendant:: NodeTest |
[descendant-or-self:: NodeTest]Axis |
== |
descendant-or-self:: NodeTest |
[namespace:: NodeTest]Axis |
== |
namespace:: NodeTest |
Reverse axes:
[preceding-sibling:: NodeTest]Axis |
== |
[let $e := . in $e/parent::node()/child:: NodeTest [.<<$e]]Expr |
[preceding:: NodeTest]Axis |
== |
[ancestor-or-self::node()/preceding-sibling::node()/descendant-or-self:: NodeTest]Expr |
All other reverse axes are part of the core:
[parent:: NodeTest]Axis |
== |
parent:: NodeTest |
[ancestor:: NodeTest]Axis |
== |
ancestor:: NodeTest |
[ancestor-or-self:: NodeTest]Axis |
== |
ancestor-or-self:: NodeTest |
Introduction
A node test is a condition applied on the nodes selected by an axis step. Node tests are described by the following grammar productions.
[77 (XQuery)] | NodeTest |
::= | KindTest | NameTest |
[78 (XQuery)] | NameTest |
::= | QName | Wildcard |
[79 (XQuery)] | Wildcard |
::= | "*" |
Core Grammar
The Core grammar productions for node tests are:
[59 (Core)] | NodeTest |
::= | KindTest | NameTest |
[60 (Core)] | NameTest |
::= | QName | Wildcard |
[61 (Core)] | Wildcard |
::= | "*" |
Notation
For convenience, we will use the grammar non-terminals Prefix, and LocalPart, both of which are NCNames, in some of the inference rules. They are defined by the following grammar productions.
[18 (Formal)] | Prefix |
::= | NCName |
[19 (Formal)] | LocalPart |
::= | NCName |
Introduction
A predicate consists of an expression, called a predicate expression, enclosed in square brackets.
[82 (XQuery)] | Predicate |
::= | "[" Expr "]" |
Notation
Normalization of predicates uses the following auxiliary mapping rule: []Predicates.
Predicates in path expressions are normalized with a special mapping rule:
[Expr]Predicates | |||
== | |||
|
Note that the semantics of predicates whose parameter is a numeric value also works for other numeric than integer values, in which case the op:numeric-equal
returns false when compared to a position. For example the expression //a[3.4]
is allowed and always returns the empty sequence)
The corresponding Section in the [XPath/XQuery] document just contains examples.
[73 (XQuery)] | AbbrevForwardStep |
::= | "@"? NodeTest |
[76 (XQuery)] | AbbrevReverseStep |
::= | ".." |
Here are normalization rules for the abbreviated syntax.
[ @ NameTest ]Expr |
== |
attribute :: NameTest |
Introduction
[XPath/XQuery] supports operators to construct and combine sequences. A sequence is an ordered collection of zero or more items. An item is either an atomic value or a node.
[31 (XQuery)] | Expr |
::= | ExprSingle ("," ExprSingle)* |
[49 (XQuery)] | RangeExpr |
::= | AdditiveExpr ( "to" AdditiveExpr )? |
Core Grammar
The Core grammar production for sequence expressions is:
[30 (Core)] | Expr |
::= | ExprSingle ("," ExprSingle)* |
A sequence expression is normalized into a sequence of normalized single expressions:
The type of the sequence expression is the sequence over the types of the individual expressions.
Each expression in the sequence is evaluated and the resulting values are concatenated into one sequence.
The default rules for propogating errors, described in [3.3 Error Handling] apply to sequence expressions.
The range operator is normalized to the fs:to
function.
The static semantics of the fs:to
function is defined in [Functions and Operators].
The dynamic semantics of the op:to operator is defined in [Functions and Operators].
The error semantics of the op:to operator is defined in [Functions and Operators].
Introduction
[80 (XQuery)] | FilterExpr |
::= | PrimaryExpr PredicateList |
Core Grammar
There are no Core grammar productions for filter expressions as they are normalized to other Core expressions.
When predicates are applied on a primary expression, the input sequence is processed in sequence order and the context is bound as in the case of forward axes. In that case, the sequence can contain both nodes and atomic values.
[PrimaryExpr PredicateList "[" Numeric "]"]Expr | ||
== | ||
|
When predicates are applied on a primary expression, the input sequence is processed in sequence order and the context variable is bound to each item in the input sequence, which may contain both nodes and atomic values.
[PrimaryExpr PredicateList "[" Expr "]"]Expr | ||||
== | ||||
|
There are no additional static type rules for filter expressions.
There are no additional dynamic evaluation rules for filter expressions.
There are no additional error semantics rules for filter expressions.
[XPath/XQuery] provides several operators for combining sequences of nodes.
[52 (XQuery)] | UnionExpr |
::= | IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )* |
[53 (XQuery)] | IntersectExceptExpr |
::= | InstanceofExpr ( ("intersect" | "except") InstanceofExpr )* |
Notation
The union, intersect, and except expressions are normalized into function calls to the appropriate functions. The mapping function []SequenceOp is defined by the following tables:
SequenceOp | [SequenceOp]SequenceOp |
"union" | op:union |
"|" | op:union |
"intersect" | op:intersect |
"except" | op:except |
[Expr1 SequenceOp Expr2]Expr |
== |
fs:apply-ordering-mode ([SequenceOp]SequenceOp ( [Expr1]Expr, [Expr2]Expr )) |
The static semantics of the operators that combine sequences are defined in [7.2.14 The op:union, op:intersect, and op:except operators].
The dynamic semantics for function calls is given in [4.1.5 Function Calls].
The error semantics for function calls is given in [4.1.5 Function Calls].
[XPath/XQuery] provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.
[50 (XQuery)] | AdditiveExpr |
::= | MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )* |
[51 (XQuery)] | MultiplicativeExpr |
::= | UnionExpr ( ("*" | "div" | "idiv" | "mod") UnionExpr )* |
[58 (XQuery)] | UnaryExpr |
::= | ("-" | "+")* ValueExpr |
[59 (XQuery)] | ValueExpr |
::= | ValidateExpr | PathExpr | ExtensionExpr |
Core Grammar
The Core grammar production for arithmetic expressions is:
[48 (Core)] | ValueExpr |
::= | ValidateExpr | StepExpr | ExtensionExpr |
Notation
The mapping functions []ArithOp and UnaryArithOp are defined by the following tables:
ArithOp | [ArithOp]ArithOp |
"+" | fs:plus |
"-" | fs:minus |
"*" | fs:times |
"div" | fs:div |
"mod" | fs:mod |
UnaryArithOp | [UnaryArithOp]UnaryArithOp |
"+" | fs:unary-plus |
"-" | fs:unary-minus |
Core Grammar
There are no Core grammar productions for arithmetic expressions as they are normalized to other Core expressions.
The normalization rules for all the arithmetic operators except idiv
first atomize each argument by applying fn:data
and then apply the internal function fs:convert-operand
to each argument. If the first argument to this function has type xdt:untypedAtomic
, then the first argument is cast to a double, otherwise it is returned unchanged. The overloaded internal function
corresponding to the arithmetic operator is then applied to the two converted arguments. The table above maps the operators to the corresponding internal function. The mapping from the overloaded internal functions to the corresponding monomorphic function is given in [B.2 Mapping of Overloaded Internal Functions].
[Expr1 ArithOp Expr2]Expr | ||||
== | ||||
|
The normalization rules for the idiv
operator are similar, but instead of casting arguments with type xdt:untypedAtomic
to xs:double
, they are cast to xs:integer
.
[Expr1 idiv Expr2]Expr |
||||
== | ||||
|
The unary operators are mapped similarly.
[+ Expr]Expr |
== |
fs:unary-plus (fs:convert-operand (fn:data ([Expr]Expr), 1.0E0)) |
[- Expr]Expr |
== |
fs:unary-minus (0, fs:convert-operand (fn:data ([Expr]Expr), 1.0E0)) |
The static semantics for function calls is given in [4.1.5 Function Calls].
The dynamic semantics for function calls is given in [4.1.5 Function Calls].
The error semantics for function calls is given in [4.1.5 Function Calls].
Introduction
Comparison expressions allow two values to be compared. [XPath/XQuery] provides four kinds of comparison expressions, called value comparisons, general comparisons, node comparisons, and order comparisons.
[48 (XQuery)] | ComparisonExpr |
::= | RangeExpr ( (ValueComp |
[61 (XQuery)] | ValueComp |
::= | "eq" | "ne" | "lt" | "le" | "gt" | "ge" |
[60 (XQuery)] | GeneralComp |
::= | "=" | "!=" | "<" | "<=" | ">" | ">=" |
[62 (XQuery)] | NodeComp |
::= | "is" | "<<" | ">>" |
Notation
The mapping function []ValueOp is defined by the following table:
ValueOp | [ValueOp]ValueOp |
"eq " |
fs:eq |
"ne " |
fs:ne |
"lt " |
fs:lt |
"le " |
fs:le |
"gt " |
fs:gt |
"ge " |
fs:ge |
Core Grammar
There are no Core grammar productions for value comparisons as they are normalized to other Core expressions.
The normalization rules for the value comparison operators first atomize each argument by applying fn:data
and then apply the internal function fs:convert-operand
defined in [7.1.3 The fs:convert-operand function]. If the first argument to this function has type xdt:untypedAtomic
, then the first argument is cast to a string, otherwise it is
returned unchanged. The overloaded internal function corresponding to the value comparison operator is then applied to the two converted arguments. The table above maps the value operators to the corresponding internal function. The mapping from the overloaded internal functions to the corresponding monomorphic function is given in [B.2 Mapping of Overloaded Internal Functions].
[Expr1 ValueOp Expr2]Expr | ||||
== | ||||
|
The static semantics for function calls is given in [4.1.5 Function Calls]. The comparison functions all have return type xs:boolean
, as specified in [Functions and Operators].
The dynamic semantics for function calls is given in [4.1.5 Function Calls].
The error semantics rules for function calls is given in [4.1.5 Function Calls].
Introduction
General comparisons are defined by adding existential semantics to value comparisons. The operands of a general comparison may be sequences of any length. The result of a general comparison is always true
or false
.
Notation
For convenience, GeneralOp denotes the operators "=
", "!=
", "<
", "<=
", ">
", or ">=
".
The function []GeneralOp is defined by the following table:
GeneralOp | [GeneralOp]GeneralOp |
"= " |
fs:eq |
"!= " |
fs:ne |
"< " |
fs:lt |
"<= " |
fs:le |
"> " |
fs:gt |
">= " |
fs:ge |
Core Grammar
There are no Core grammar productions for general comparisons as they are normalized to existentially quantified Core expressions.
The normalization rule for a general comparison expression first atomizes each argument by applying fn:data
and then applies the existentially quantified some expression to each sequence. The internal function fs:convert-operand
is applied to each pair of atomic values. If the first argument to this function has type xdt:untypedAtomic
, then the first argument is cast to type of the
second argument. If the second argument has type xdt:untypedAtomic
, the first argument is cast to a string. The overloaded internal function corresponding to the general comparison operator is then applied to the two converted values.
[Expr1 GeneralOp Expr2]Expr | |||||
== | |||||
|
Core Grammar
There are no Core grammar productions for node comparisons as they are normalized to other Core expressions.
The normalization rules for node comparisons map each argument expression and then apply the internal function corresponding to the node comparison operator. The internal function are defined in [B.2 Mapping of Overloaded Internal Functions].
The static semantics for the internal functions are defined in [B.2 Mapping of Overloaded Internal Functions].
The dynamic semantics for internal function is defined in [B.2 Mapping of Overloaded Internal Functions].
The error semantics rules for function calls is given in [4.1.5 Function Calls].
Introduction
A logical expression is either an and-expression or an or-expression. The value of a logical expression is always one of the boolean values: true
or false
.
[46 (XQuery)] | OrExpr |
::= | AndExpr ( "or" AndExpr )* |
[47 (XQuery)] | AndExpr |
::= | ComparisonExpr ( "and" ComparisonExpr )* |
Core Grammar
The Core grammar productions for logical expressions are:
[44 (Core)] | OrExpr |
::= | AndExpr ( "or" AndExpr )* |
[45 (Core)] | AndExpr |
::= | CastableExpr ( "and" CastableExpr )* |
The normalization rules for "and
" and "or
" first get the effective boolean value of each argument, then apply the appropriate Core operator.
The logical expressions require that each subexpression have type xs:boolean
. The result type is also xs:boolean
.
The dynamic semantics of logical expressions is non-deterministic. This non-determinism permits implementations to use short-circuit evaluation strategies when evaluating logical expressions. In the expression, Expr1 and
Expr2, if either expression raises an error or evaluates to false, the entire expression may raise an error or evaluate to false. In the expression, Expr1 or
Expr2, if either expression raises an error or evaluates to true, the entire expression may raise an error or evaluate to true.
[XPath/XQuery] supports two forms of constructors: a direct constructor, which supports literal XML syntax for elements, attributes, and text nodes, and a computed constructor, which can be used to construct element and attribute nodes, possibly with computed names, and also document and text nodes. All direct constructors are normalized into computed constructors, i.e., there are no direct-constructor expressions in the Core.
Introduction
The static and dynamic semantics of the direct forms of element and attribute constructors are specified on the equivalent computed element and attribute constructors.
Notation
The auxiliary mapping rules []ElementContent, and []ElementContent-unit are defined in this section and are used for the normalization of the content of direct element constructors.
Core Grammar
The Core grammar productions for constructors are:
[70 (Core)] | ComputedConstructor |
::= | CompDocConstructor |
[28 (Core)] | EnclosedExpr |
::= | "{" Expr "}" |
There are no Core grammar productions for direct XML element or attribute constructors as they are normalized to computed constructors.
We start with the rules for normalizing a direct element constructors' content. Literal XML character data (CDATA) is assumed to be processed directly at parsing level so it does not require any formal treatment. We distinguish between direct element constructors that contain only one element-content unit and those that contain more than one element-content unit. An element-content unit is a contiguous sequence of literal characters (character references, escaped braces, and predefined entity references), one enclosed expression, one direct element constructor, one XML comment, or one XML processing instruction. Here are three direct element constructors that each contain one element-content unit:
<date>{ xs:date("2003-03-18") }</date> <name>Dizzy Gillespe</name> <comment><!-- Just a comment --></comment>
The first contains one enclosed expression, the second contains one contiguous sequence of characters, and the third contains one XML comment.
After boundary-space is stripped, the next example contains six element-content units:
<address> <!-- Dizzy's address --> { 123 }-0A <street>Roosevelt Ave.</street> Flushing, NY { 11368 } </address>
It contains one XML comment, followed by one enclosed expression that contains the integer 123, one contiguous sequence of characters ("-0A "), one direct XML element constructor, one contiguous sequence of characters (" Flushing, NY"), and one enclosed expression that contains the integer 11368. Evaluation of that constructor will result in the following element.
<address><!-- Dizzy's address -->123-0A <street>Roosevelt Ave.</street> Flushing, NY 11368</address>
Adjacent element-content units are convenient because they permit arbitrary interleaving of text and atomic data. During evaluation, atomic values are converted to text nodes containing the string representations of the atomic values, and then adjacent text nodes are concatenated together. In the example above, the integer 123 is converted to a string and concatenated with "-0A" and the result is a single text node containing "123-0A".
In general, we do not want to convert all atomic values to text nodes, especially when performing static-type analysis, because we lose useful type information. For example, if we normalize the first example above as follows, we lose the important information that the user constructed a date value, not just a text node containing an arbitrary string:
<date>{ xs:date("2003-03-18") }</date> (normalization that loses type information) == element date { text { "2003-03-18" } }
To preserve useful type information, we distinguish between direct element constructors that contain one element-content unit and those that contain more than one (because multiple element-content units commonly denote concatenatation of atomic data and text). Below are two examples of normalization for element constructors.
<date>{ xs:date("2003-03-18") }</date> == element date { xs:date("2003-03-18") } <address> <!-- Dizzy's address --> { 123 }-0A <street>Roosevelt Ave.</street> Flushing, NY { 11368 } </address> == element address { fs:item-sequence-to-node-sequence( comment { " Dizzy's address "}, 123, text { "-0A "}, element street {"Roosevelt Ave."}, text { " Flushing, NY " }, 11368 ) }
Given the distinction between direct element constructors that we made above, we give two normalization rules for a direct element constructor's content. If the direct element constructor contains exactly one element-content unit, we simply normalize that unit by applying the normalization rule for the element content:
[ ElementContent1 ]ElementContent-unit |
== |
[ ElementContent1 ]ElementContent |
If the direct element constructor contains more than one element-content unit, we normalize each unit individually and construct a sequence of the normalized results interleaved with empty text nodes. The empty text nodes guarantee that the results of evaluating consecutive element-content units can be distinguished. Then we apply the function fs:item-sequence-to-node-sequence
. Section
3.7.1 Direct Element ConstructorsXQ specifies the rules for converting a sequence of atomic values and nodes into a sequence of nodes before element construction. The Formal Semantics function fs:item-sequence-to-node-sequence
implements these conversion rules.
[ElementContent1 ..., ElementContentn]ElementContent-unit, n > 1 |
== |
fs:item-sequence-to-node-sequence ([ ElementContent1 ]ElementContent , text { "" }, ..., text { "" }, [ ElementContentn]ElementContent) |
We need to distinguish between multiple element-content units, because the rule for converting sequences of atomic values into strings apply to sequences within distinct enclosed expressions. The empty text nodes are eliminated during evaluation of fs:item-sequence-to-node-sequence
when consecutive text nodes are coalesced into a single text node. The text node guarantees that a whitespace character will not be inserted between atomic values
computed by distinct enclosed expressions. For example, here is an expression, its normalization, and the resulting XML value:
<example>{ 1 }{ 2 }</example> == element example { fs:item-sequence-to-node-sequence ((1, text {""}, 2)) } ==> <example>12</example>
In the absence of the empty text node, the expression would evaluate to the following incorrect value:
<example>{ 1 }{ 2 }</example> (incorrect normalization) == element example { fs:item-sequence-to-node-sequence ((1, 2)) } (incorrect value) ==> <example>1 2</example>
Now that we have explained the normalization rules for direct element content, we give the rules for the two forms of direct XML element constructors. Note that the direct attribute constructors are normalized twice: the []NamespaceAttrs normalizes the namespace-declaration attributes and []Attribute normalizes all other attributes that are not namespace-declaration attributes.
[ < QName AttributeList > ElementContent* </ QName S? > ]Expr |
== |
element [QName]Expr{ [ AttributeList ]NamespaceAttrs , [ AttributeList ]Attribute , [ ElementContent* ]ElementContent } |
[ < QName AttributeList /> ]Expr |
== |
element [QName]Expr { [ AttributeList ]NamespaceAttrs , [ AttributeList ]Attribute } |
Next, we give the normalization rules for each element-content unit. The normalization rule for a contiguous sequence of characters assumes:
that the significant whitespace characters in element constructors have been preserved, as described in [4.7.1.4 Whitespace in Element Content];
that character references have been resolved to individual characters and predefined entity references have been resolved to sequences of characters, and
that the rule is applied to the longest contiguous sequence of characters.
The following normalization rule takes the longest consecutive sequence of individual characters that include literal characters, escaped curly braces, character references, and predefined entity references and normalizes the character sequence as a text node containing the string of characters.
[(Char | "{{" | "}}" | CharRef | PredefinedEntityRef)+]ElementContent |
== |
text { fn:codepoints-to-string ((Char | "{{" | "}}" | CharRef | PredefinedEntityRef)+) } |
XML processing instructions and comments in element content are normalized by applying the standard normalization rules for expressions, which appear in [4.7.2 Other Direct Constructors].
[DirPIConstructor]ElementContent |
== |
[DirPIConstructor]Expr |
[DirCommentConstructor]ElementContent |
== |
[DirCommentConstructor]Expr |
An enclosed expression in element content is normalized by normalizing each individual expression in its expression sequence and then constructing a sequence of the normalized values:
[ { Expr1, ..., Exprn } ]ElementContent |
== |
[ Expr1 ]Expr , ..., [ Exprn]Expr |
There are no additional static type rules for direct XML element or attribute constructors.
There are no additional dynamic evaluation rules for direct XML element or attribute constructors.
There are no additional error semantics rules for direct XML element or attribute constructors.
Like literal XML element constructors, literal XML attribute constructors are normalized to computed attribute constructors.
Notation
The auxiliary mapping rules []Attribute, []AttributeContent, and []AttributeContent-unit, are defined in this section and are used for the normalization of the content of direct attribute constructors.
Direct attributes may contain namespace-declaration attributes. The normalization rules for attributes ignore namespace-declaration attributes -- they are handled by the normalization rules in [4.7.1.2 Namespace Declaration Attributes].
An AttributeList is normalized by the following rule, which maps each of the individual attribute-value expressions in the attribute list and constructs a sequence of the normalized values.
[
|
|||
== | |||
|
Namespace-declaration attributes, i.e., those attributes whose prefix is xmlns
are ignored by mapping them to the empty sequence.
|
||
== | ||
() |
All attributes that are not namespace-declaration attributes are mapped to computed attribute constructors.
|
||
== | ||
attribute [Prefix:LocalPart ]Expr { [AttributeValue]AttributeContent} |
As with literal XML elements, we need to distinguish between direct attribute constructors that contain one attribute-content unit and those that contain multiple attribute-content units, because the rule for converting sequences of atomic values into strings are applied to sequences within distinct enclosed expressions. If the direct attribute constructor contains exactly one attribute-content unit, we simply normalize that unit by applying the normalization rule for the attribute content:
[ AttributeValueContent1 ]AttributeContent-unit |
== |
[AttributeValueContent1]AttributeContent |
If the direct attribute constructor contains more than one attribute-content unit, we normalize each unit individually and construct a sequence of the normalized results interleaved with empty text nodes. The empty text nodes guarantee that the results of evaluating consecutive attribute-content units can be distinguished. Then we apply the function fs:item-sequence-to-untypedAtomic
, which applies the appropriate
conversion rules to the normalized attribute content:
[ AttributeValueContent1 ..., AttributeValueContentn ]AttributeContent-unit, n > 1 |
== |
fs:item-sequence-to-untypedAtomic ([ AttributeValueContent1 ]AttributeContent , text { "" }, ..., text {""}, [ AttributeValueContentn]AttributeContent) |
Literal characters, escaped curly braces, character references, and predefined entity references in attribute content are treated as in element content. In addition, the normalization rule for characters in attributes assumes:
that an escaped single or double quote is converted to an individual single or double quote.
The following normalization rules take the longest consecutive sequence of individual characters that include literal characters, escaped curly braces, escaped quotes, character references, predefined entity references, and escaped single and double quotes and normalizes the character sequence as a string.
[( Char | CharRef | EscapeQuot | EscapeApos | PredefinedEntityRef ) +]AttributeContent |
== |
fn:codepoints-to-string (( Char | CharRef | EscapeQuot | EscapeApos | PredefinedEntityRef )+) |
We normalize an enclosed expression in attribute content by normalizing each individual expression in its expression sequence and then construct a sequence of the normalized values:
[ { Expr0, ..., Exprn } ]AttributeContent |
== |
([ Expr0 ]Expr , ..., [ Exprn]Expr) |
Notation
The auxiliary mapping rules []NamespaceAttr, and []NamespaceAttrs are defined in this section and are used for the normalization of namespace declaration attributes.
Direct attributes may contain namespace-declaration attributes. The normalization rules for namespace-declaration attributes ignore all non-namespace attributes -- they are handled by the normalization rules in [4.7.1.1 Attributes].
An AttributeList containing namespace-declaration attributes is normalized by the following rule, which maps each of the individual namespace-declaration attributes in the attribute list and constructs a sequence of the normalized namespace attribute values.
[
|
|||
== | |||
|
Attributes whose prefix is not xmlns
are ignored by mapping them to the empty sequence.
|
||
== | ||
() |
Namespace-declaration attributes are normalized to local namespace declarations (CompElemNamespace).
|
||
== | ||
namespace LocalPart { [AttributeValue]AttributeContent} |
The rules for normalizing element content are given above in [4.7.1 Direct Element Constructors].
Section 3.7.1.4 Boundary WhitespaceXQ describes how whitespace in element and attribute constructors is processed depending on the value of the xmlspace
declaration in the query prolog. the Formal Semantics assumes that the rules for handling whitespace are applied prior to normalization rules, for example, during parsing of a query. Therefore, there are no formal rules for handling whitespace.
[103 (XQuery)] | DirPIConstructor |
::= | "<?" PITarget (S DirPIContents)? "?>" |
[104 (XQuery)] | DirPIContents |
::= | (Char* - (Char* '?>' Char*)) |
[101 (XQuery)] | DirCommentConstructor |
::= | "<!--" DirCommentContents "-->" |
[102 (XQuery)] | DirCommentContents |
::= | ((Char - '-') | ('-' (Char - '-')))* |
A literal XML processing instruction is normalized into a computed processing-instruction constructor; its character content is converted to a string as in attribute content.
A literal XML comment is normalized into a computed comment constructor; its character content is converted to a string as in attribute content.
There are no additional static type rules for direct processing-instruction or comment constructors.
There are no additional dynamic evaluation rules for direct processing-instruction or comment constructors.
There are no additional error semantics rules for direct processing-instruction constructors.
[107 (XQuery)] | ComputedConstructor |
::= | CompDocConstructor |
[109 (XQuery)] | CompElemConstructor |
::= | (("element" QName "{") | ("element" "{" Expr "}" "{")) ContentExpr? "}" |
[110 (XQuery)] | ContentExpr |
::= | Expr |
Notation
Local namespace declarations may occur explicitly in a computed element constructor or may be the result of normalizing namespace-declaration attributes contained in direct element constructors. For local element declarations that occur explicitly in a query, the immediately enclosing expression of the local namespace declaration (CompElemNamespace) must be a computed element constructor; otherwise, as specified in [XPath/XQuery], a static error is raised.
Core Grammar
The Core grammar productions for computed element constructors are:
[72 (Core)] | CompElemConstructor |
::= | (("element" QName "{") | ("element" "{" Expr "}" "{")) ContentExpr "}" |
[73 (Core)] | ContentExpr |
::= | Expr |
If the content expression is missing, the computed element constructor is normalized as if its content expression was the empty sequence.
Computed element constructors using the fs:item-sequence-to-node-sequence
function over their content expression.
[element QName { Expr }]Expr |
== |
element QName { fs:item-sequence-to-node-sequence ([Expr]Expr) } |
When the name of the element is also computed, the normalization rule applies atomization to the name expression.
[element { Expr1 } { Expr2 }]Expr |
== |
element { fn:data ([Expr1]Expr) }{ fs:item-sequence-to-node-sequence ([Expr2]Expr) } |
The normalization rules of direct element and attribute constructors leave us with only the computed forms of constructors. The static semantic for constructors is defined on all the computed forms. The computed element constructor itself has two forms: one in which the element name is a literal QName, and the other in which the element name is a computed expression.
A computed element constructor creates a new element with either the type annotationXQ xdt:untyped
(in strip construction mode), or with the type annotationXQ xs:anyType
(in preserve construction mode). The content expression must return a sequence of nodes with attribute nodes
at the beginning.
|
||||
|
||||
statEnv |- element QName { Expr } : element QName of type xs:anyType |
|
||||
|
||||
statEnv |- element QName { Expr } : element QName of type xdt:untyped |
In case the element name is computed as well, the name expression must be of type xs:QName
, xs:string
, or xdt:untypedAtomic
.
|
||||||
|
||||||
statEnv |- element { Expr1 } { Expr2 } : element of type xs:anyType |
|
||||||
|
||||||
statEnv |- element { Expr1 } { Expr2 } : element of type xdt:untyped |
The following rules take a computed element constructor expression and construct an element node. The dynamic semantics for computed element constructors is the most complex of all expressions in XQuery. Here is how to read the rule below.
First, the element's content expression is partitioned into the local namespace declarations and all other expressions, and the local namespace declarations are evaluated, yielding a sequence of namespace bindings. The static environment is extended to include the new namespace bindings, which are all active. In Section 3.7.1.2 Namespace Declaration AttributesXQ, it is implementation-defined whether undeclaration of namespace prefixes (by setting the namespace prefix to the zero-length string) in an element constructor is supported. In the dynamic semantics below, we assume all local namespace declarations declare a binding of a prefix to a URI.
Second, the function fs:item-sequence-to-node-sequence
is applied to the element's content expression (excluding local namespace declarations); this function call is evaluated in the new static and dynamic environment. Recall from [4.7.1 Direct Element Constructors] that during normalization, we do not convert the content of direct element constructors that contain one element-content unit. This
guarantees that useful type information is preserved for static analysis. Since the conversion function fs:item-sequence-to-node-sequence
was not applied to all element constructors during normalization, we have to apply it at evaluation time. (Obviously, it is possible to elide the application of fs:item-sequence-to-node-sequence
injected during normalization and the application injected during
evaluation.) The resulting value Value0 must match zero-or-more attributes followed by zero-or-more element, text, processing-instruction or comment nodes.
Third, The namespace bindings are concatenated with the list of active namespaces in the namespace environment statEnv.namespace and the namespaces corresponding to the element's name and all attributes names. The resulting sequence is the sequence of namespace bindings for the element.
|
|||||||||||
|
|||||||||||
statEnv; dynEnv |- element QName { Expr } => Value0 |
The dynamic evaluation of an element constructor with a computed name is similar. There is one additional rule that checks that the value of the element's name expression matches xs:QName
.
|
||||||||||||
|
||||||||||||
statEnv; dynEnv |- element { Expr1 } { Expr2 } => Value1 |
The default rules for propogating errors, described in [3.3 Error Handling] apply to element constructors. In addition, a computed element constructor with a computed name raises a type error if the name value is not a xs:QName
.
|
||
|
||
dynEnv |- element { Expr1 } { Expr2 } raises typeError |
Both forms of computed element constructors raise a type error if the element's content is not a sequence of attributes followed by a sequence of element, text, comment, and processing-instruction nodes, or a sequence of atomic values.
[111 (XQuery)] | CompAttrConstructor |
::= | (("attribute" QName "{") | ("attribute" "{" Expr "}" "{")) Expr? "}" |
Core Grammar
The Core grammar production for computed attribute constructors is:
[74 (Core)] | CompAttrConstructor |
::= | (("attribute" QName "{") | ("attribute" "{" Expr "}" "{")) Expr "}" |
Computed attribute constructors are normalized by mapping their name and content expression in a similar way as computed element constructors. The normalization rule uses the fs:item-sequence-to-untypedAtomic
function.
[attribute QName { Expr }]Expr |
== |
attribute QName { fs:item-sequence-to-untypedAtomic ([Expr]Expr) } |
[attribute { Expr1 } { Expr2 }]Expr |
== |
attribute { fn:data ([Expr1]Expr) } { fs:item-sequence-to-untypedAtomic ([Expr2]Expr) } |
The normalization rules for direct attribute constructors leave us with only the computed form of the attribute constructors. Like in a computed element constructor, a computed attribute constructor has two forms: one in which the attribute name is a literal QName, and the other in which the attribute name is a computed expression.
In the case of attribute constructors, the type annotationXQ is always xdt:untypedAtomic
.
|
|||
|
|||
statEnv |- attribute QName { Expr } : attribute QName of type xdt:untypedAtomic |
|
|||||
|
|||||
statEnv |- attribute { Expr1 } { Expr2 } : attribute of type xdt:untypedAtomic |
The following rules take a computed attribute constructor expression and construct an attribute node. The rules are similar to those rules for element constructors. First, the attribute's name is expanded into a qualified name. Second, the function fs:item-sequence-to-untypedAtomic
is applied to the content expression and this function call is evaluated in the dynamic environment. Recall from [4.7.3.2 Computed Attribute Constructors] that during normalization, we do not convert the content of direct attribute constructors that contain one attribute-content unit. This guarantees that useful type information is preserved for static analysis. Since the conversion function fs:item-sequence-to-untypedAtomic
was not applied to all attribute constructors during normalization, we have to apply it
at evaluation time. (As before, it is possible to elide the application of fs:item-sequence-to-untypedAtomic
injected during normalization and the application injected during evaluation.)
|
|||
|
|||
dynEnv |- attribute QName { Expr } => attribute expanded-QName of type xdt:untypedAtomic { Value } |
|
|||||
|
|||||
dynEnv |- attribute { Expr1 } { Expr2 } => attribute QName1 of type xdt:untypedAtomic { Value2 } |
The default rules for propogating errors, described in [3.3 Error Handling] apply to attribute constructors. In addition, an attribute constructor with a computed name raises a type error if the name value is not a xs:QName
. the xmlns
namespace.
|
||
|
||
dynEnv |- attribute { Expr1 } { Expr2 } raises typeError |
A dynamic error is raised if the namespace URI of the attribute's QName, whether known statically or dynamically, is in the xmlns
namespace.
|
|||
|
|||
dynEnv |- attribute { Expr1 } { Expr2 } raises dynError |
[108 (XQuery)] | CompDocConstructor |
::= | "document" "{" Expr "}" |
Core Grammar
The Core grammar production for a computed document constructor is:
[71 (Core)] | CompDocConstructor |
::= | "document" "{" Expr "}" |
A document node constructor contains an expression, which must evaluate to a sequence of element, text, comment, or processing-instruction nodes. Section 3.7.3.3 Document Node ConstructorsXQ specifies the rules for converting a sequence of atomic values and nodes into a sequence of nodes before document construction. The built-in function [7.1.7 The fs:item-sequence-to-node-sequence function] implements this conversion.
[document { Expr }]Expr |
== |
document { fs:item-sequence-to-node-sequence ([Expr]Expr) } |
The static semantics checks that the type of the argument expression is a sequence of element, text, processing-instruction, and comment nodes. The type of the entire expression is the most general document
type, because the document constructor erases all type annotationXQ on its content nodes.
|
|||
|
|||
statEnv |- document { Expr } : document |
The dynamic semantics checks that the argument expression evaluates to a value that is a sequence of element, text, processing-instruction, or comment nodes. The entire expression evaluates to a new document node value. If the construction mode is set to strip
, the type annotationXQ for all the nodes in content of a document node are erased.
|
||||
|
||||
dynEnv |- document { Expr } => document { Value } |
|
|||||
|
|||||
dynEnv |- document { Expr } => document { Value2 } |
The default rules for propogating errors, described in [3.3 Error Handling] apply to document node constructors. In addition, if the argument expression evaluates to a value that is not a sequence of element, text, processing-instruction, or comment nodes, a type error is raised.
[112 (XQuery)] | CompTextConstructor |
::= | "text" "{" Expr "}" |
Core Grammar
The Core grammar production for a computed text constructor is:
[75 (Core)] | CompTextConstructor |
::= | "text" "{" Expr "}" |
A text node constructor contains an expression, which must evaluate to an xs:string
value. Section 3.7.3.4 Text Node ConstructorsXQ specifies the rules for converting a sequence of atomic values into a string prior to construction of a text node. Each node is replaced by its string value. For each adjacent sequence of one or more atomic values returned by an enclosed expression, a untyped atomic value is
constructed, containing the canonical lexical representation of all the atomic values, with a single blank character inserted between adjacent values. As formal specification of these conversion rules is not instructive, [7.1.8 The fs:item-sequence-to-untypedAtomic function] implements this conversion.
[text { Expr }]Expr |
== |
text { (fs:item-sequence-to-untypedAtomic-text (fn:data ([Expr]Expr))) cast as xs:string ? } |
The static semantics checks that the argument expression has type xs:string
or empty
. The type of the entire expression is an optional text node type, as the text node constructor returns the empty sequence if its argument is the empty sequence.
If the argument expression returns the empty sequence, the text node constructor returns the empty sequence.
If the argument expression returns a value of type xs:string
, the text node constructor returns a text node with that string as content.
|
||
|
||
dynEnv |- text { Expr } => text { Value } |
The default rules for propogating errors, described in [3.3 Error Handling] apply to text node constructors. In addition, if the argument expression evaluates to a value that is not a string or the empty sequence, a type error is raised.
[114 (XQuery)] | CompPIConstructor |
::= | (("processing-instruction" NCName "{") | ("processing-instruction" "{" Expr "}" "{")) Expr? "}" |
Core Grammar
The Core grammar production for computed processing-instruction constructors is:
[77 (Core)] | CompPIConstructor |
::= | (("processing-instruction" NCName "{") | ("processing-instruction" "{" Expr "}" "{")) Expr? "}" |
Computed processing-instruction constructors are normalized by mapping their name and content expression in the same way that computed element and attribute constructors are normalized.
[processing-instruction NCName { Expr }]Expr |
== |
processing-instruction NCName { fs:item-sequence-to-untypedAtomic-PI ([Expr]Expr) } |
[processing-instruction { Expr1 } { Expr2 }]Expr |
== |
processing-instruction { fn:data ([Expr1]Expr) } { fs:item-sequence-to-untypedAtomic-PI ([Expr2]Expr) } |
The static typing rules for processing-instruction constructors are straightforward.
statEnv |- Expr : xdt:untypedAtomic |
|
statEnv |- processing-instruction NCName { Expr } : processing-instruction |
statEnv |- Expr1 : (xs:NCName | xs:string | xdt:untypedAtomic ) statEnv |- Expr2 : xdt:untypedAtomic |
|
statEnv |- processing-instruction { Expr1 } { Expr2 } : processing-instruction |
The dynamic evaluation rules for computed processing instructions are straightforward.
|
||
|
||
dynEnv |- processing-instruction NCName { Expr } => processing-instruction NCName { Value } |
|
|||||
|
|||||
dynEnv |- processing-instruction { Expr1 } { Expr2 } => processing-instruction NCName1 { Value2 } |
|
|||||
|
|||||
dynEnv |- processing-instruction { Expr1 } { Expr2 } => processing-instruction NCName1 { Value2 } |
|
|||||
|
|||||
dynEnv |- processing-instruction { Expr1 } { Expr2 } => processing-instruction NCName1 { Value2 } |
The default rules for propogating errors, described in [3.3 Error Handling] apply to computed processing-instruction constructors. The normalization rules guarantee that a dynamic error is raised if the target expression is not a string or a QName.
[113 (XQuery)] | CompCommentConstructor |
::= | "comment" "{" Expr "}" |
Core Grammar
The Core grammar production for computed comment constructors is:
[76 (Core)] | CompCommentConstructor |
::= | "comment" "{" Expr "}" |
Computed comment constructors are normalized by mapping their content expression.
[comment { Expr }]Expr |
== |
comment { (fs:item-sequence-to-untypedAtomic-comment ([Expr]Expr)) cast as xs:string } |
The static typing rule for computed comment constructors is straightforward.
The dynamic evaluation rule for computed comment constructors is straightforward.
|
||
|
||
dynEnv |- comment { Expr } => comment { Value } |
The default rules for propogating errors, described in [3.3 Error Handling] apply to computed comment constructors.
The effect of in-scope namespaces on constructed elements is specified in [4.7.1 Direct Element Constructors] and [4.7.3.1 Computed Element Constructors].
Introduction
[XPath/XQuery] provides [For/FLWR] expressions for iteration, for binding variables to intermediate results, and filtering bound variables according to a predicate.
A FLWORExpr in XQuery 1.0 consists of a sequence of ForClauses and LetClauses, followed by an optional WhereClause, followed by the , as described by the following grammar productions. Each variable binding is preceded by an optional type declaration which specify the type expected for the variable.
The dynamic semantics of the ordering mode in FLWOR expressions is not specified formally. The dynamic semantics is not specified formally as it would require the introduction of tuples, which are not supported in the [XPath/XQuery] data model.
[33 (XQuery)] | FLWORExpr |
::= | (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle |
[34 (XQuery)] | ForClause |
::= | "for" "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle)* |
[36 (XQuery)] | LetClause |
::= | "let" "$" VarName TypeDeclaration? ":=" ExprSingle ("," "$" VarName TypeDeclaration? ":=" ExprSingle)* |
[116 (XQuery)] | TypeDeclaration |
::= | "as" SequenceType |
[35 (XQuery)] | PositionalVar |
::= | "at" "$" VarName |
[37 (XQuery)] | WhereClause |
::= | "where" ExprSingle |
[38 (XQuery)] | OrderByClause |
::= | ("order" "by" | "stable" "order" "by") OrderSpecList |
[39 (XQuery)] | OrderSpecList |
::= | OrderSpec ("," OrderSpec)* |
[40 (XQuery)] | OrderSpec |
::= | ExprSingle OrderModifier |
[41 (XQuery)] | OrderModifier |
::= | ("ascending" | "descending")? (("empty" "greatest") | ("empty" "least"))? ("collation" URILiteral)? |
[4 (XPath)] | ForExpr |
::= | SimpleForClause "return" ExprSingle |
[5 (XPath)] | SimpleForClause |
::= | "for" "$" VarName "in" ExprSingle ("," "$" VarName "in" ExprSingle)* |
Core Grammar
The Core grammar productions for FLWOR expressions are:
[32 (Core)] | FLWORExpr |
::= | (ForClause | LetClause) "return" ExprSingle |
[33 (Core)] | ForClause |
::= | "for" "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle |
[35 (Core)] | LetClause |
::= | "let" "$" VarName TypeDeclaration? ":=" ExprSingle |
[34 (Core)] | PositionalVar |
::= | "at" "$" VarName |
[79 (Core)] | TypeDeclaration |
::= | "as" SequenceType |
[36 (Core)] | OrderByClause |
::= | ("order" "by" | "stable" "order" "by") OrderSpecList |
[37 (Core)] | OrderSpecList |
::= | OrderSpec ("," OrderSpec)* |
[38 (Core)] | OrderSpec |
::= | ExprSingle OrderModifier |
[39 (Core)] | OrderModifier |
::= | ("ascending" | "descending")? (("empty" "greatest") | ("empty" "least"))? ("collation" URILiteral)? |
Notation
Individual [For/FLWR] clauses are normalized by means of the auxiliary normalization rules:
Where FLWORClause can be any either a ForClause, a LetClause, a WhereClause, or an OrderByClause. The OrderByClause is discussed in [4.8.4 Order By and Return Clauses].
Normalized FLWOR expressions restrict a For and Let clause to bind only one variable. Otherwise, the Core FLWOR expression is the same as the XQuery FLWOR expression.
Notation
The auxiliary rule []FLWOR(Expr) normalizes a For, Let, or Where clause in a FLWORExpr expression. Note that the rule takes the remainder of the FLWOR expression (other For, Let, or Where clauses and the Return clause) as a parameter in Expr.
The [For/FLWR] expressions include the FLWORExpr of XQuery and the ForExpr of XPath. The normalization rule for ForExpr is simple: It simply unrolls a ForExpr that binds multiple variables into nested ForExprs, each of which bind one variable.
[for VarRef0 in Expr0, ..., VarRefn in Exprn return Expr ]Expr | ||||
== | ||||
|
Full FLWORExpr expressions are normalized to nested core expressions using two sets of normalization rules. Note that some of the rules also accept ungrammatical FLWORExprs such as "where Expr1 return Expr2". This does not matter, as normalization is always applied on parsed [XPath/XQuery] expressions, and ungrammatical FLWORExprs would be rejected by the parser beforehand.
The first set of rules is applied on a full [For/FLWR] expression, splitting it at the clause level, then applying further normalization on each separate clause.
[ (ForClause | LetClause | WhereClause | OrderByClause) FLWORExpr ]Expr |
== |
[(ForClause | LetClause | WhereClause | OrderByClause)]FLWOR([FLWORExpr]Expr) |
[ (ForClause | LetClause | WhereClause | OrderByClause) return Expr ]Expr |
== |
[(ForClause | LetClause | WhereClause | OrderByClause)]FLWOR([Expr]Expr) |
Then each [For/FLWR] clause is normalized separately. A ForClause may bind more than one variable, whereas a For expression in the [XPath/XQuery] Core binds and iterates over only one variable. Therefore, a ForClause is normalized to nested for expressions:
[
|
|||
== | |||
|
Note that the additional Expr parameter of the auxiliary normalization rule is used as the final return expression.
Likewise, a LetClause clause is normalized to nested let expressions, each of which binds one variable:
[
|
|||
== | |||
|
A WhereClause is normalized to an IfExpr, with the else-branch returning the empty sequence:
Example
The following simple example illustrates, how a FLWORExpr is normalized. The for
expression in the example below is used to iterate over two collections, binding variables $i
and $j
to items in these collections. It uses a let
clause to binds the local variable $k
to the sum of both numbers, and a where
clause to select only those numbers that have a sum equal to or greater than the integer 5
.
for $i as xs:integer in (1, 2), $j in (3, 4) let $k := $i + $j where $k >= 5 return <tuple> <i> { $i } </i> <j> { $j } </j> </tuple>
By the first set of rules, this is normalized to (except for the operators and element constructor which are not treated here):
for $i as xs:integer in (1, 2) return for $j in (3, 4) return let $k := $i + $j return if ($k >= 5) then <tuple> <i> { $i } </i> <j> { $j } </j> </tuple> else ()
For each binding of $i
to an item in the sequence (1 , 2)
the inner for
expression iterates over the sequence (3 , 4)
to produce tuples ordered by the ordering of the outer sequence and then by the ordering of the inner sequence. This core expression eventually results in the following document fragment:
(<tuple> <i>1</i> <j>4</j> </tuple>, <tuple> <i>2</i> <j>3</j> </tuple>, <tuple> <i>2</i> <j>4</j> </tuple>)
A single for
expression is typed as follows: First Type1 of the iteration expression Expr1 is inferred. Then the prime type of Type1, prime(Type1), is computed. This is a union over all item types in
Type1 (See [8.4 Judgments for FLWOR and other expressions on sequences]). With the variable component of the static environment statEnv extended with VarRef1 as type prime(Type1),
the type Type2 of Expr2 is inferred. Because the for
expression iterates over the result of Expr1, the final type of the iteration is Type2 multiplied with the possible number of items in Type1 (one,
?
, *
, or +
). This number is determined by the auxiliary type-function quantifier(Type1).
|
|||
|
|||
statEnv |- for VarRef1 in Expr1 return Expr2 : Type2 · quantifier(Type1) |
When a positional variable Variablepos is present, the static environment is also extended with the positional variable typed as an xs:integer
.
|
|||
|
|||
statEnv |- for VarRef1 at VarRefpos in Expr1 return Expr2 : Type2 · quantifier(Type1) |
When a type declaration is present, the static semantics also checks that the type of the input expression is a subtype of the declared type and extends the static environment by typing VarRef1 with type Type0. This semantics is specified by the following typing rule.
|
|||||
|
|||||
statEnv |- for VarRef1 as SequenceType in Expr1 return Expr2 : Type2 · quantifier(Type1) |
The last rule contains a For expression that contains a type declaration and a positional variable. When the positional variable is present, the static environment is also extended with the positional variable typed as an integer.
|
|||||
|
|||||
statEnv |- for VarRef1 as SequenceType at VarRefpos in Expr1 return Expr2 : Type2 · quantifier(Type1) |
Example
For example, if $example
is bound to the sequence 10.0, 1.0E1, 10
of type xs:decimal, xs:float, xs:integer
, then the query
for $s in $example return $s * 2
is typed as follows:
(1) prime(xs:decimal, xs:float, xs:integer) = xs:decimal | xs:float | xs:integer (2) quantifier(xs:decimal, xs:float, xs:integer) = + (3) $s : xs:decimal | xs:float | xs:integer (4) $s * 2 : xs:decimal | xs:float | xs:integer (5) result-type : ( xs:decimal | xs:float | xs:integer ) +
This result-type is not the most specific type possible. It does not take into account the order of elements in the input type, and it ignores the individual and overall number of elements in the input type. The most specific type possible is: element out {element one {}}, element out {element two {}}, element out {element three {}}
. However, inferring such a specific type for arbitrary input types and arbitrary return clauses requires significantly more complex type inference rules. In
addition, if put into the context of an element, the specific type violates the "unique particle attribution" restriction of XML schema, which requires that an element must have a unique content model within a particular context.
The evaluation of a for
expression distinguishes two cases: If the iteration expression Expr1 evaluates to the empty sequence, then the entire expression evaluates to the empty sequence:
Otherwise, the iteration expression Expr1, is evaluated to produce the sequence Item1, ..., Itemn. For each item Itemi in this sequence, the body of the for
expression Expr2 is evaluated in the
environment dynEnv extended with VarRef1 bound to Itemi. This produces values Valuei, ..., Valuen which are concatenated to produce the result sequence.
|
||||||
|
||||||
dynEnv |- for VarRef in Expr1 return Expr2 => Value1 ,..., Valuen |
The following rule is the same as the rule above, but includes the optional positional variable VarRefpos. If present, VarRefpos is bound to the position of the item in the input sequence, i.e., the value i.
|
||||||
|
||||||
dynEnv |- for VarRef at VarRefpos in Expr1 return Expr2 => Value1 ,..., Valuen |
When a type declaration is present, the dynamic semantics also checks that each item in the result of evaluating Expr1 matches the declared type. This semantics is specified by the following dynamic rule.
|
||||||||
|
||||||||
dynEnv |- for VarRef as SequenceType in Expr1 return Expr2 => Value1 ,..., Valuen |
The last rule covers a For expresstion that contains a type declaration and a positional variable.
|
|||||||||
|
|||||||||
dynEnv |- for VarRef as SequenceType at VarRefpos in Expr1 return Expr2 => Value1 ,..., Valuen |
Note that this definition allows non-deterministic evaluation of the resulting sequence, since the judgments above the inference rule can be evaluated in any order.
If evaluation of the first expression raises an error, the entire expression raises an error. This rule applies to all forms of a For expression, i.e., those with or without a type declaration or positional variable.
dynEnv |- Expr1 raises Error |
|
dynEnv |- for VarRef TypeDeclaration? PositionalVar? in Expr1 return Expr2 raises Error |
If any evaluation of the body of the for expression raises an error, then the entire expression raises an error. This rule applies to for expressions with or without the type declaration.
|
||||
|
||||
dynEnv |- for VarRef TypeDeclaration? in Expr1 return Expr2 raises Error |
|
||||
|
||||
dynEnv |- for VarRef TypeDeclaration? at VarRefpos in Expr1 return Expr2 raises Error |
When a type declaration is present, a type error is raised if any item in the result of evaluating Expr1 does not match the declared type.
|
||||
|
||||
dynEnv |- for VarRef as SequenceType PositionalVar1? in Expr1 return Expr2 raises typeError |
Example
Note that if the expression in the return
clause results in a sequence, sequences are never nested in the [XPath/XQuery] data model. For instance, in the following for expression:
for $i in (1,2) return (<i> {$i} </i>, <negi> {-$i} </negi>)
each iteration in the for
results in a sequence of two elements, which are then concatenated and flattened in the resulting sequence:
(<i>1</i>, <negi>-1</negi>, <i>2</i>, <negi>-2</negi>)
A let
expression extends the type environment statEnv with Variable1 of type Type1 inferred from Expr1, and infers the type of Expr2 in the extended environment to produce the result type Type2.
|
||
|
||
statEnv |- let VarRef := Expr1 return Expr2 : Type2 |
When a type declaration is present, the static semantics also checks that the type of the input expression is a subtype of the declared type and extends the static environment by typing Variable1 with type Type0. This semantics is specified by the following static rule.
|
|||||
|
|||||
statEnv |- let VarRef1 as SequenceType := Expr1 return Expr2 : Type2 |
A let
expression extends the dynamic environment dynEnv with Variable bound to Value1 returned by Expr1, and evaluates Expr2 in the extended environment to produce Value2.
|
|||
|
|||
dynEnv |- let VarRef1 := Expr1 return Expr2 => Value2 |
When a type declaration is present, the dynamic semantics also checks that the result of evaluating Expr1 matches the declared type. This semantics is specified as the following dynamic rule.
|
|||||
|
|||||
dynEnv |- let VarRef1 as SequenceType := Expr1 return Expr2 => Value2 |
The default rules for propogating errors, described in [3.3 Error Handling] apply to let expressions. In addition, in the case that a type declaration is present, a type error is raised if the result of evaluating Expr1 does not match the declared type.
|
||||
|
||||
dynEnv |- let VarRef1 as SequenceType := Expr1 return Expr2 raises typeError |
Example
Note the use of the environment discipline to define the scope of each variable. For instance, in the following nested let
expression:
let $k := 5 return let $k := $k + 1 return $k+1
the outermost let
expression binds variable $k
to the integer 5
in the environment, then the expression $k+1
is computed, yielding value 6
, to which the second variable $k
is bound. The expression then results in the final integer 7
.
Introduction
The dynamic semantics of the OrderByClause is not specified formally. The dynamic semantics is not specified formally as it would require the introduction of tuples, which are not supported in the [XPath/XQuery] data model. The dynamic semantics of the order-by clause can be found in Section 3.8.3 Order By and Return ClausesXQ.
Because an OrderByClause does not effect the type of a FLWORExpr expression, the static semantics of a FLWORExpr expression with an OrderByClause is equivalent to the static semantics of an equivalent FLWORExpr in which the OrderByClause is omitted but a gt
comparison is applied.
Notation
To define normalization of OrderBy, the following auxiliary mapping rule is used.
[OrderSpecList]OrderSpecList |
== |
[LetClause ... LetClause] |
which specify that OrderSpecList is mapped to Expr.
An OrderByClause is normalized to a Let clause, nested For expressions, and atomization, which guarantees that the OrderSpecList is well typed. Note that if evaluated dynamically, the normalization of OrderByClause given here does not express the required sorting semantics, but this normalization does provide the correct static type. Notably, the normalization rule uses the gt
operation, which implies that the ordering criteria is typed using the same static
typing rules, taking into account existential quantification, atomization and type promotion.
[ stable? order by OrderSpecList]FLWOR(Expr) |
== |
[OrderSpecList]OrderSpecList return Expr |
Each OrderSpec is normalized the auxiliary atomization normalization rule.
[Expr OrderModifier, OrderSpecList]OrderSpecList | |||||
== | |||||
|
Introduction
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.
[89 (XQuery)] | OrderedExpr |
::= | "ordered" "{" Expr "}" |
[90 (XQuery)] | UnorderedExpr |
::= | "unordered" "{" Expr "}" |
Core Grammar
The Core grammar productions for ordered/unordered expressions are:
[67 (Core)] | OrderedExpr |
::= | "ordered" "{" Expr "}" |
[68 (Core)] | UnorderedExpr |
::= | "unordered" "{" Expr "}" |
OrderedExpr (resp. UnorderedExpr) expressions are normalized to OrderedExpr (resp. UnorderedExpr) expressions in the [XPath/XQuery] core.
OrderedExpr and UnorderedExpr expressions only have an effect on the static context. The effect on the evaluation of its subexpression(s) is captured using the fs:apply-ordering-mode
function, which introduced during normalization of axis steps, union
, intersect
, and except
expressions, and FLWOR expressions that have no order by
clause.
OrderedExpr and UnorderedExpr expressions set the ordering mode in the static context to ordered
or unordered
.
Introduction
A conditional expression supports conditional evaluation of one of two expressions.
[45 (XQuery)] | IfExpr |
::= | "if" "(" Expr ")" "then" ExprSingle "else" ExprSingle |
Core Grammar
The Core grammar production for the conditional expression is:
[43 (Core)] | IfExpr |
::= | "if" "(" Expr ")" "then" ExprSingle "else" ExprSingle |
[if (Expr1) then Expr2 else Expr3]Expr | |
== | |
|
statEnv |- Expr1 : xs:boolean statEnv |- Expr2 : Type2 statEnv |- Expr3 : Type3 |
|
statEnv |- if (Expr1) then Expr2 else Expr3 : (Type2 | Type3) |
If the conditional's boolean expression Expr1 evaluates to true, Expr2 is evaluated and its value is produced. If the conditional's boolean expression evaluates to false, Expr3 is evaluated and its value is produced. Note that the existence of two separate evaluation rules ensures that only one branch of the conditional is evaluated.
dynEnv |- Expr1 => true dynEnv |- Expr2 => Value2 |
|
dynEnv |- if (Expr1) then Expr2 else Expr3 => Value2 |
dynEnv |- Expr1 => false dynEnv |- Expr3 => Value3 |
|
dynEnv |- if Expr1 then Expr2 else Expr3 => Value3 |
If the conditional's boolean expression raises an error, then the conditional expression raises an error.
If the conditional's boolean expression Expr1 evaluates to true, and Expr2 raises an error, then the conditional expression raises an error. Conversely, if the conditional's boolean expression evaluates to false, and Expr3 raises an error, then the conditional raises an error.
Introduction
[XPath/XQuery] defines two quantification expressions:
[42 (XQuery)] | QuantifiedExpr |
::= | (("some" "$") | ("every" "$")) VarName TypeDeclaration? "in" ExprSingle ("," "$" VarName TypeDeclaration? "in" ExprSingle)* "satisfies" ExprSingle |
[6 (XPath)] | QuantifiedExpr |
::= | (("some" "$") | ("every" "$")) VarName "in" ExprSingle ("," "$" VarName "in" ExprSingle)* "satisfies" ExprSingle |
Core Grammar
The Core grammar production for quantified expressions is:
[40 (Core)] | QuantifiedExpr |
::= | (("some" "$") | ("every" "$")) VarName TypeDeclaration? "in" ExprSingle ("," "$" VarName TypeDeclaration? "in" ExprSingle)* "satisfies" ExprSingle |
The quantified expressions are normalized into nested Core quantified expressions, each of which binds one variable.
[some VarRef1 in Expr1, ..., VarRefn in Exprn satisfies Expr]Expr | |||||
== | |||||
|
[every VarRef1 in Expr1, ..., VarRefn in Exprn satisfies Expr]Expr | |||||
== | |||||
|
The static semantics of the quantified expressions uses the prime operator on types, which is explained in [8.4 Judgments for FLWOR and other expressions on sequences]. These rules are similar to those for For expressions in [4.8.2 For expression].
|
||||
|
||||
statEnv |- some VarRef1 in Expr1 satisfies Expr2 : xs:boolean |
The next rule is for SomeExpr with the optional type declaration.
|
||||||
|
||||||
statEnv |- some VarRef1 as SequenceType in Expr1 satisfies Expr2 : xs:boolean |
The next rule is for EveryExpr without the optional type declaration.
|
||||
|
||||
statEnv |- every VarRef1 in Expr1 satisfies Expr2 : xs:boolean |
The next rule is for EveryExpr with the optional type declaration.
|
||||||
|
||||||
statEnv |- every VarRef1 as SequenceType in Expr1 satisfies Expr2 : xs:boolean |
The existentially quantified "some" expression yields true if any evaluation of the satisfies expression yields true. The existentially quantified "some" expression yields false if every evaluation of the satisfies expression is false. A quantified expression may raise an error if any evaluation of the satisfies expression raises an error. The dynamic semantics of quantified expressions is non-deterministic. This non-determinism permits implementations to use short-circuit evaluation strategies when evaluating quantified expressions.
|
||||
|
||||
dynEnv |- some VarRef1 in Expr1 satisfies Expr2 => true |
The next rule is for SomeExpr with the optional type declaration, in which some evaluation of the satisfies expression yields true.
|
||||||
|
||||||
dynEnv |- some VarRef1 as SequenceType in Expr1 satisfies Expr2 => true |
The next rule is for SomeExpr without the optional type declaration, in which all evaluations of the satisfies expression yields false.
|
||||||
|
||||||
dynEnv |- some VarRef1 in Expr1 satisfies Expr2 => false |
The next rule is for SomeExpr with the optional type declaration, in which all evaluations of the satisfies expression yields false.
|
|||||||||
|
|||||||||
dynEnv |- some VarRef1 as SequenceType in Expr1 satisfies Expr2 => false |
The universally quantified "every" expression yields false if any evaluation of the satisfies expression yields false. The universally quantified "every" expression yields true if every evaluation of the satisfies expression is true.
|
||||
|
||||
dynEnv |- every VarRef1 in Expr1 satisfies Expr2 => false |
The next rule is for EveryExpr with the optional type declaration, in which some evaluation of the satisfies expression yields false.
|
||||||
|
||||||
dynEnv |- every VarRef1 as SequenceType in Expr1 satisfies Expr2 => false |
The next rule is for EveryExpr in which all evaluations of the satisfies expression yields true.
|
||||||
|
||||||
dynEnv |- every VarRef1 in Expr1 satisfies Expr2 => true |
The next rule is for EveryExpr with the optional type declaration in which all evaluations of the satisfies expression yields true.
|
|||||||||
|
|||||||||
dynEnv |- every VarRef1 as SequenceType in Expr1 satisfies Expr2 => true |
An existentially quantified expression raises an error if:
evaluation of the first expression raises an error,
any evaluation of the satisfies expression raises an error.
|
||
|
||
dynEnv |- some VarRef1 TypeDeclaration? in Expr1 satisfies Expr2 raises Error |
|
||||
|
||||
dynEnv |- some VarRef1 TypeDeclaration? in Expr1 satisfies Expr2 raises Error |
|
||||
|
||||
dynEnv |- every VarRef1 in Expr1 satisfies Expr2 raises Error |
An existentially quantified expression raises a type error if evaluation of the first expression yields a value, and some item in this value does not match the declared type of the variable.
Introduction
Expressions on SequenceTypes are expressions whose semantics depends on the type of some of the sub-expressions to which they are applied. The syntax of SequenceType expressions is described in [3.5.3 SequenceType Syntax].
[54 (XQuery)] | InstanceofExpr |
::= | TreatExpr ( "instance" "of" SequenceType )? |
Introduction
The SequenceType expression "Expr instance of SequenceType" is true if and only if the result of evaluating expression Expr is an instance of the type referred to by SequenceType.
An InstanceofExpr expression is normalized into a TypeswitchExpr expression. Note that the following normalization rule uses a variable $fs:new, which is a newly created variable which must not conflict with any variables already in scope. This variable is necessary to comply with the syntax of typeswitch expressions in the core [XPath/XQuery], but is never used.
[43 (XQuery)] | TypeswitchExpr |
::= | "typeswitch" "(" Expr ")" CaseClause+ "default" ("$" VarName)? "return" ExprSingle |
[44 (XQuery)] | CaseClause |
::= | "case" ("$" VarName "as")? SequenceType "return" ExprSingle |
Introduction
The typeswitch expression chooses one of several expressions to evaluate based on the dynamic type of an input value.
Each branch of a typeswitch expression may have an optional VarRef, which is bound to the value of the input expression. This variable is optional in [XPath/XQuery] but mandatory in the [XPath/XQuery] Core. One of the reasons for having this variable is that it is assigned a specific type for the corresponding branch.
Core Grammar
The Core grammar productions for typeswitch
are:
[41 (Core)] | TypeswitchExpr |
::= | "typeswitch" "(" Expr ")" CaseClause+ "default" ("$" VarName)? "return" ExprSingle |
[42 (Core)] | CaseClause |
::= | "case" ("$" VarName "as")? SequenceType "return" ExprSingle |
Notation
To define normalization of case clauses to the [XPath/XQuery] core, the following auxiliary mapping rule is used.
[CaseClause]Case |
== |
CaseClause |
specifies that CaseClause is mapped to CaseClause, in the [XPath/XQuery] type system.
Normalization of a typeswitch expression guarantees that every branch has an associated VarRef. The following normalization rule adds a newly created variable that does not appear in the rest of the query. Note that $fs:new is a newly generated variable that must not conflict with any variables already in scope and that is not used in any of the sub-expressions.
[
|
|||||
== | |||||
|
Notation
The following auxiliary grammar production is used to identify branches of the typeswitch.
[79 (Formal)] | CaseRules |
::= | ("case" "$" VarName "as" SequenceType "return" Expr CaseRules) | ("default" "$" VarName "return" Expr) |
The following judgment
is used in the static of typeswitch. It indicates that under the environment statEnv, and with the input type of the typeswitch being Type1, the given case rule yields the type Type.
The following judgment
is used in the dynamic semantics of typeswitch. It indicates that under the environment dynEnv, with the input value of the typeswitch being Value1, the given case rules yields the value Value2.
The static typing rules for the typeswitch expression are simple. Each case clause and the default clause of the typeswitch is typed independently. The type of the entire typeswitch expression is the union of the types of all the clauses.
|
|||||||||
|
|||||||||
|
To type one case clause, the case variable is assigned the type of the case clause CaseType and the body of the clause is typed in the extended environment. Thus, the type of a case clause is independent of the type of the input expression.
|
||||
|
||||
statEnv |- Type0 case case VarRef as SequenceType return Expr : Type |
To type the default clause, the variable is assigned the type of the input expression and the body of the default clause is typed in the extended environment.
|
||
|
||
statEnv |- Type0 case default VarRef return Expr : Type |
The evaluation of a typeswitch proceeds as follows. First, the input expression is evaluated, yielding an input value. The effective case is the first case
clause such that the input value matches the SequenceType in the case
clause. The return
clause of the effective case is evaluated and the value of the return
expression is the value of the typeswitch expression.
|
|||
|
|||
dynEnv |- typeswitch (Expr) CaseRules => Value1 |
If the value matches the sequence type, the following rule applies: It extends the environment by binding the variable Variable to Value0 and evaluates the body of the return
clause.
|
|||||
|
|||||
dynEnv |- Value0 against case VarRef as SequenceType return Expr CaseRules => Value1 |
If the value does not match the sequence type, the current case is not evaluated, and the remaining case rules are evaluated order by applying the inference rule recursively.
|
||
|
||
dynEnv |- Value0 against case SequenceType VarRef return Expr CaseRules => Value1 |
The last rule states that the default
branch of a typeswitch expression always evaluates to the value of its return
clause.
|
|||
|
|||
dynEnv |- Value0 against default VarRef return Expr => Value1 |
The default rules for propogating errors, described in [3.3 Error Handling] apply to the typeswitch expression. In particular, if evaluation of the input expression or evaluation of any case rule raises an error, then the typeswitch expression raises an error.
Introduction
The cast
expression can be used to convert a value to a specific datatype. It changes both the type and value of the result of an expression, and can only be applied to an atomic value.
[57 (XQuery)] | CastExpr |
::= | UnaryExpr ( "cast" "as" SingleType )? |
[115 (XQuery)] | SingleType |
::= | AtomicType "?"? |
Core Grammar
The Core grammar productions for cast
expressions are:
[47 (Core)] | CastExpr |
::= | ValueExpr ( "cast" "as" SingleType )? |
[78 (Core)] | SingleType |
::= | AtomicType "?"? |
The normalization of cast applies atomization to its argument. The type declaration asserts that the result is a single atomic value. The second normalization rule applies when the target type is optional.
[Expr cast as AtomicType ]Expr | ||
== | ||
|
[Expr cast as AtomicType? ]Expr | ||||
== | ||||
|
The static typing rule of cast
expression is as follows. The type of a core cast
expression is always the target type. Note that a cast
expression can fail at run-time if the given value cannot be cast to the target type.
|
statEnv |- Expr cast as AtomicType : AtomicType |
The dynamic semantics of cast
expressions is defined in Section 17 CastingFO. The semantics of cast expressions depends on the type of the input value and on the target type. For any source and target primitive types, the casting table in Section 17 CastingFO indicates whether the cast from the source type to the
target type is permitted. When a cast is permitted, the detailed dynamic rules for cast in Section 17 CastingFO are applied. These rules are not specified further here.
The default rules for propogating errors, described in [3.3 Error Handling] apply to cast expressions.
[56 (XQuery)] | CastableExpr |
::= | CastExpr ( "castable" "as" SingleType )? |
Castable expressions check whether a value can be cast to a given type.
Core Grammar
The Core grammar production for castable is:
[46 (Core)] | CastableExpr |
::= | CastExpr ( "castable" "as" SingleType )? |
The normalization of castable simply maps its expression argument.
[Expr castable as AtomicType]Expr | ||
== | ||
|
[Expr castable as AtomicType?]Expr | ||
== | ||
|
The type of a core castable
expression is always a boolean.
|
statEnv |- Expr castable as AtomicType : xs:boolean |
If casting succeeds, then the castable
expression evaluates to true.
|
|||
|
|||
|
If casting raises a dynamic error, 'castable as' evaluates to false.
|
||
|
||
|
The default rules for propogating errors, described in [3.3 Error Handling] apply to castable expression.
Constructor functions provide an alternative syntax for casting.
Constructor functions for atomic types are normalized to explicit cast as
expressions.
[AtomicType(Expr)]Expr |
== |
[Expr cast as AtomicType? ]Expr |
[55 (XQuery)] | TreatExpr |
::= | CastableExpr ( "treat" "as" SequenceType )? |
Introduction
The expression "Expr treat as SequenceType", can be used to change the static type of the result of an expression without changing its value. The treat-as expression raises a dynamic error if the dynamic type of the input value does not match the specified type.
Treat as expressions are normalized to typeswitch expressions. Note that the following normalization rule uses a variable $fs:new, which is a newly created variable that does not conflict with any variables already in scope.
[63 (XQuery)] | ValidateExpr |
::= | (("validate" "{") | ("validate" ValidationMode "{")) Expr "}" |
[145 (XQuery)] | ValidationMode |
::= | "lax" | "strict" |
Core Grammar
The Core grammar productions for validate are:
[49 (Core)] | ValidateExpr |
::= | (("validate" "{") | ("validate" ValidationMode "{")) Expr "}" |
[108 (Core)] | ValidationMode |
::= | "lax" | "strict" |
A validate
expression validates its argument with respect to the in-scope schema definitions, using the schema validation process described in [Schema Part 1]. The argument to a validate expression must be either element or document node. Validation replaces all nodes with new nodes that have their own identity, the type annotationXQ, and default values created during the
validation process.
A validate expression with no validation mode is normalized into a validate expression with the validation mode set to strict.
Static typing of the validate operation is defined by the following rule. Note the use of a subtyping check to ensure that the type of the expression to validate is either an element or a well-formed document node (i.e., with only one root element and no text nodes). The type of the expression to validate may be a union of more than one element type. We apply the with mode judgment to each element type to determine the meaning of that element type with the given validation mode, which yields a new element type. The result type is the union over all new element types.
|
|||||||||||
|
|||||||||||
statEnv |- validate ValidationMode { Expr } : Type1 |
The normative dynamic semantics of validation is specified in Section 3.13 Validate ExpressionsXQ. The effect of validation of a data model value is equivalent to:
serialization of the data model, as described in [Data Model Serialization], followed by
validation of the serialized value into a Post-Schema Validated Infoset, as described in [Schema Part 1], followed by
construction of a new data model value, as described in [Data Model].
The above steps are expressed formally by the "erasure" and "annotation" judgments. Formally, validation removes existing type annotations from nodes ("erasure"), and it re-validates the corresponding data model instance, possibly adding new type annotations to nodes ("annotation"). Both erasure and annotation are described formally in [E Auxiliary Judgments for Validation]. Indeed, the conjunction of erasure and annotation provides a formal model for a
large part of actual schema validation. The semantics of the validate
expression is specified as follows.
In the first premise below, the expression to validate is evaluated. The resulting value must be an element or document node. The second premise constructs a new value in which all existing type annotations have been erased. The third premise determines the element type that corresponds to the element node's name in the given validation mode. The last premise validates erased element node with the type against which it is validated, using the annotate as judgment, yielding the final validated element.
|
||||||
|
||||||
dynEnv |- validate ValidationMode { Expr } => ElementValue3 |
The rule for validating a document node is similar to that for validating an element node.
|
||||||
|
||||||
dynEnv |- validate ValidationMode { Expr } => document { ElementValue3 } |
The default rules for propogating errors, described in [3.3 Error Handling] apply to the validate expression.
Introduction
An extension expression is an expression whose semantics are implementation-defined. An extension expression consists of one or more pragmas, followed by an expression enclosed in curly braces.
[64 (XQuery)] | ExtensionExpr |
::= | Pragma+ "{" Expr? "}" |
[65 (XQuery)] | Pragma |
::= | "(#" S? QName PragmaContents "#)" |
[66 (XQuery)] | PragmaContents |
::= | (Char* - (Char* '#)' Char*)) |
Core Grammar
The Core grammar productions for ExtensionExpr are:
[50 (Core)] | ExtensionExpr |
::= | Pragma+ "{" Expr? "}" |
[51 (Core)] | Pragma |
::= | "(#" S? QName PragmaContents "#)" |
[52 (Core)] | PragmaContents |
::= | (Char* - (Char* '#)' Char*)) |
Extension expressions are normalized as extension expressions in the [XPath/XQuery] core.
If the extension expression does not contain any expression, this is normalized into an extension expression with a call to the fn:error
function.
[Pragma+ { }]Expr |
== |
Pragma+ { fn:error () } |
The QName of a pragma must resolve to a namespace URI and local name, using the statically known namespaces. If at least one of the pragmas is recognized, the dynamic semantics is implementation-defined.
|
||
|
||
dynEnv |- Pragma+ { Expr } => Value |
If none of the pragmas are recognized the dynamic semantics of an ExtensionExpression are the same as evaluating the given expression.
If at least one of the pragmas is recognized, the static semantics are implementation-defined.
If none of the pragmas are recognized, the static semantics are the same as for the input expression. In both cases, the static typing must be applied on the input expression, possibly raising corresponding static type errors.
The organization of this section parallels the organization of Section 4 Modules and PrologsXQ.
Introduction
XQuery supports modules as defined in Section 4 Modules and PrologsXQ. A main moduleXQ contains a PrologXQ followed by a query bodyXQ. A query has exactly one main module. In a main module, the query bodyXQ can be evaluated, and its value is the result of the query. A library moduleXQ contains a module declaration followed by a PrologXQ.
The Prolog is a sequence of declarations that affect query processing. The Prolog can be used, for example, to declare namespace prefixes, import types from XML Schemas, and declare functions and variables. Namespace declarations and schema imports always precede function and variable declarations, as specified by the following grammar productions.
[1 (XQuery)] | Module |
::= | VersionDecl? (MainModule | LibraryModule) |
[3 (XQuery)] | MainModule |
::= | Prolog QueryBody |
[4 (XQuery)] | LibraryModule |
::= | ModuleDecl Prolog |
[6 (XQuery)] | Prolog |
::= | ((Setter | Import | NamespaceDecl | DefaultNamespaceDecl) Separator)* ((VarDecl | FunctionDecl | OptionDecl) Separator)* |
[7 (XQuery)] | Setter |
::= | BoundarySpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | OrderingModeDecl | EmptyOrderDecl | CopyNamespacesDecl |
[8 (XQuery)] | Import |
::= | SchemaImport | ModuleImport |
[9 (XQuery)] | Separator |
::= | ";" |
[30 (XQuery)] | QueryBody |
::= | Expr |
Function declarations are globally scoped, that is, the use of a function name in a function call may precede declaration of the function. Variable declarations are lexically scoped, i.e., variable declarations must precede variable uses.
Core Grammar
The Core grammar productions for the prolog are:
[1 (Core)] | Module |
::= | VersionDecl? (MainModule | LibraryModule) |
[3 (Core)] | MainModule |
::= | Prolog QueryBody |
[4 (Core)] | LibraryModule |
::= | ModuleDecl Prolog |
[6 (Core)] | Prolog |
::= | ((Setter | Import | NamespaceDecl | DefaultNamespaceDecl) Separator)* ((VarDecl | FunctionDecl | OptionDecl) Separator)* |
[7 (Core)] | Setter |
::= | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | OrderingModeDecl | EmptyOrderDecl | CopyNamespacesDecl |
[8 (Core)] | Import |
::= | SchemaImport | ModuleImport |
[9 (Core)] | Separator |
::= | ";" |
[29 (Core)] | QueryBody |
::= | Expr |
Notation
The XQuery Prolog requires that declarations appear in a particular order. In the Formal Semantics, it is simpler to assume the declarations can appear in any order, as it does not change their semantics -- we simply assume that an XQuery parser has enforced the required order.
The Prolog contains a variety of declarations that specify the initial static and dynamic context of the query. The following formal grammar productions represent any Prolog declaration.
[80 (Formal)] | PrologDeclList |
::= | (PrologDecl Separator)* |
[81 (Formal)] | PrologDecl |
::= | DefaultCollationDecl |
The function []PrologDecl takes a prolog declaration and maps it into its equivalent declaration in the Core grammar.
[PrologDecl1]PrologDecl |
== |
PrologDecl2 |
The following auxiliary judgments are applied when statically processing the declarations in the prolog. The effect of the judgment is to process each prolog declaration in order, constructing a new static environment from the static environment constructed from previous prolog declarations.
The judgment:
holds if under the static environment statEnv1, the sequence of prolog declarations PrologDeclList yields the static environment statEnv2 and the normalized sequence of prolog declarations in the Core grammar.
The judgment:
holds if under the static environment statEnv1, the single prolog declaration PrologDecl yields the new static environment statEnv2.
Prolog declarations are processed in the order they are encountered. The normalization of a prolog declaration PrologDecl depends on the static context processing of all previous prolog declarations. In turn, static context processing of PrologDecl depends on the normalization of the PrologDecl. For example, because variables are lexically scoped, the normalization and static context processing of a variable declaration depends on the normalization and static context processing of all previous variable declarations. Therefore, the normalization phase and static context processing are interleaved, with normalization preceding static context processing for each prolog declaration.
The following inference rules express this dependency. The first rule specifies that for an empty sequence of prolog declarations, the initial static environment is the default static context.
The next rule interleaves normalization and static context processing. The result of static context processing and normalization is a static context and the normalized prolog declarations.
|
||||
|
||||
statEnv |- PrologDecl ; PrologDeclList =>stat statEnv2 with PrologDecl1 ; PrologDeclList1 |
Static typing of a main module follows context processing and normalization. Context processing and normalization of a main module applies the rules above to the prolog, then using the resulting static environment statEnv, the query body is normalized into a Core expression, and the static typing rules are applied to this Core expression.
|
||||
|
||||
PrologDeclList QueryBody : Type |
Notation
Similary, the judgment:
holds if under the static environment statEnv1, the sequence of prolog declarations PrologDeclList yields the static environment statEnv2 and the normalized sequence of prolog declarations in the Core grammar.
The judgment:
holds if under the dynamic environment dynEnv, the single prolog declaration PrologDecl yields the new dynamic environment dynEnv1.
The rules for initializing the dynamic context are as follows. The first rule specifies for an empty sequence of prolog declarations, the initial dynamic environment is the default dynamic context.
The second rule simply computes the dynamic environment by processing the prolog declarations in order.
|
|||
|
|||
dynEnv |- PrologDecl ; PrologDeclList =>dyn dynEnv2 |
Dynamic evalution of a main module applies the rules for dynamic-context processing to the prolog declarations, then using the resulting dynamic environment dynEnv, the dynamic evaluation rules are applied to the normalized query body.
|
||||
|
||||
|
[2 (XQuery)] | VersionDecl |
::= | "xquery" "version" StringLiteral ("encoding" StringLiteral)? Separator |
Core Grammar
The core grammar production for version declarations is:
[2 (Core)] | VersionDecl |
::= | "xquery" "version" StringLiteral ("encoding" StringLiteral)? Separator |
A version declaration specifies the applicable XQuery syntax and semantics for a module. An XQuery implementation must raise a static error when processing a query labeled with a version that the implementation does not support. The Formal Semantics is specified for XQuery 1.0 and does not specify this static error formally.
Introduction
[5 (XQuery)] | ModuleDecl |
::= | "module" "namespace" NCName "=" URILiteral Separator |
We assume that the static-context processing and dynamic-context processing described in [5 Modules and Prologs] are applied to all library modules before the normalization, static context processing, and dynamic context processing of the main module. That is, at the time an "import module" declaration is processed, we assume that the static and dynamic context of the imported module is already available. This assumption does not require or assume separate compilation of modules. An implementation might process all or some imported modules statically (i.e., before the importing module is identified) or dynamically (i.e., when the importing module is identified and processed).
Notation
We define a new judgment that maps a module's URI to the corresponding module's static environment:
We also define a new judgment that maps a module's URI to the corresponding module's dynamic environment:
Core Grammar
The core grammar production for module declarations is:
[5 (Core)] | ModuleDecl |
::= | "module" "namespace" NCName "=" URILiteral Separator |
The effect of a module declaration is to apply the static processing rules defined in [5 Modules and Prologs] to the module's prolog. The resulting static context is then available to any importing module.
The module declaration extends the prolog with a namespace declaration that binds the module's prefix to its URI, then computes the static context for the complete module.
|
|||
|
|||
|
Note that the rule above and the rules for static processing of an "import module" declaration in [5.11 Module Import] are mutually recursive.
The dynamic context processing of a module declaration is similar to that of static processing. The module declaration extends the prolog with a namespace declaration that binds the module's prefix to its URI, then computes the dynamic context for the complete module.
|
|||
|
|||
|
Note that the rule above and the rules for dynamic processing of an "import module" declaration in [5.11 Module Import] are mutually recursive.
[11 (XQuery)] | BoundarySpaceDecl |
::= | "declare" "boundary-space" ("preserve" | "strip") |
The xmlspace declaration is not specified formally as the Formal Semantics is defined on the Core language, which is an abstract, not concrete, syntax and is typically the result of parsing phase described in [3.2.1 Processing model].
[19 (XQuery)] | DefaultCollationDecl |
::= | "declare" "default" "collation" URILiteral |
Core Grammar
The core grammar production for default collation declarations is:
[18 (Core)] | DefaultCollationDecl |
::= | "declare" "default" "collation" URILiteral |
The default collation declaration is in the Core grammar, so no normalization rules are necessary.
The default collation declaration updates the collations environment of the static context. The collations environment is used by several functions in [Functions and Operators], but is otherwise not used in the Formal Semantics.
|
|||
|
|||
|
The default collation declaration does not affect the dynamic context.
[20 (XQuery)] | BaseURIDecl |
::= | "declare" "base-uri" URILiteral |
Core Grammar
The core grammar production for base uri declarations is:
[19 (Core)] | BaseURIDecl |
::= | "declare" "base-uri" URILiteral |
The base URI declaration is already in the Core grammar, so normalization rule is necessary.
A base URI declaration specifies the base URI property of the static context, which is used when resolving relative URIs within a module. A static error is raised if more than one base URI declaration is declared in a query prolog.
The base URI declaration does not affect the dynamic context.
[25 (XQuery)] | ConstructionDecl |
::= | "declare" "construction" ("preserve" | "strip") |
Core Grammar
The core grammar production for construction declarations is:
[24 (Core)] | ConstructionDecl |
::= | "declare" "construction" ("preserve" | "strip") |
The construction declaration is in the Core grammar, so no normalization rule is necessary.
The construction declaration modifies the construction mode in the static context.
statEnv1 = statEnv + constructionMode( ConstructionMode) | ||
|
||
|
The construction declaration does not have any affect on the dynamic context.
[14 (XQuery)] | OrderingModeDecl |
::= | "declare" "ordering" ("ordered" | "unordered") |
Core Grammar
The core grammar production for ordering mode declarations is:
[13 (Core)] | OrderingModeDecl |
::= | "declare" "ordering" ("ordered" | "unordered") |
[15 (XQuery)] | EmptyOrderDecl |
::= | "declare" "default" "order" ("empty" "greatest" | "empty" "least") |
Core Grammar
The core grammar production for empty order declarations is:
[14 (Core)] | EmptyOrderDecl |
::= | "declare" "default" "order" ("empty" "greatest" | "empty" "least") |
[16 (XQuery)] | CopyNamespacesDecl |
::= | "declare" "copy-namespaces" PreserveMode "," InheritMode |
[17 (XQuery)] | PreserveMode |
::= | "preserve" | "no-preserve" |
[18 (XQuery)] | InheritMode |
::= | "inherit" | "no-inherit" |
Core Grammar
The core grammar productions for copy-namespaces declarations are:
[15 (Core)] | CopyNamespacesDecl |
::= | "declare" "copy-namespaces" PreserveMode "," InheritMode |
[16 (Core)] | PreserveMode |
::= | "preserve" | "no-preserve" |
[17 (Core)] | InheritMode |
::= | "inherit" | "no-inherit" |
[21 (XQuery)] | SchemaImport |
::= | "import" "schema" SchemaPrefix? URILiteral (("at" URILiteral) ("," URILiteral)*)? |
[22 (XQuery)] | SchemaPrefix |
::= | ("namespace" NCName "=") | ("default" "element" "namespace") |
The semantics of Schema Import is described in terms of the [XPath/XQuery] type system. The process of converting an XML Schema into a sequence of type declarations is described in Section [C Importing Schemas]. This section describes how the resulting sequence of type declarations is added into the static context when the Prolog is processed.
Core Grammar
The core grammar productions for schema imports are:
[20 (Core)] | SchemaImport |
::= | "import" "schema" SchemaPrefix? URILiteral (("at" URILiteral) ("," URILiteral)*)? |
[21 (Core)] | SchemaPrefix |
::= | ("namespace" NCName "=") | ("default" "element" "namespace") |
Schema import declarations are in the Core grammar, so no normalization rules are necessary.
Notation
Some of the judgments use the following production for LocationHints.
[16 (Formal)] | LocationHints |
::= | "at" URILiteral ("," URILiteral)* |
The following auxiliary judgments are used when processing schema imports.
The judgment:
holds if under the static environment statEnv1, the sequence of type definitions Definitions yields the new static environment statEnv2.
The judgment:
holds if under the static environment statEnv1, the single definition Definition yields the new static environment statEnv2.
A schema imported into a query is first mapped into the [XPath/XQuery] type system, which yields a sequence of XQuery type definitions. The rules for mapping the imported schema begins in [C.2 Schemas as a whole]. Each type definition in an imported schema is then added to the static environment.
|
|||
|
|||
|
The schema import declaration may also assign an element/type namespace prefix to the URI of the imported schema, or assign the default element namespace to the URI of the imported schema.
|
||||
|
||||
|
|
||||
|
||||
|
An empty sequence of type definitions yields the input environment.
Each type definition is added into the static environment.
|
|||
|
|||
|
Each type, element, or attribute declaration is added respectively to the type, element and attribute declarations components of the static environment.
|
|||
|
|||
|
|
|||
|
|||
|
|
|||
|
|||
|
Note that it is a static error to import two schemas that both define the same name in the same symbol space and in the same scope, that is multiple top-level definitions of the same type, element, or attribute name raises a static error. For instance, a query may not import two schemas that include top-level element declarations for two elements with the same expanded name.
The schema import declarations do not affect the dynamic context.
[23 (XQuery)] | ModuleImport |
::= | "import" "module" ("namespace" NCName "=")? URILiteral (("at" URILiteral) ("," URILiteral)*)? |
Core Grammar
The core grammar production for module imports is:
[22 (Core)] | ModuleImport |
::= | "import" "module" ("namespace" NCName "=")? URILiteral (("at" URILiteral) ("," URILiteral)*)? |
Notation
The rules below depend on the following auxilliary functions,
The function fs:local-variables
(statEnv, URI) returns all the (expanded-QName, Type) pairs in statEnv.varType such that the URI part of the variable's expanded-QName equals the given URI, that is, the variables that
are declared locally in the module with the given namespace URI.
The function fs:local-functions
(statEnv, URI) returns all the function signatures in statEnv.funcType such that the URI part of the function's expanded-QName equals the given URI, that is, the function signatures that are declared locally in the module with the given namespace URI.
During static context processing, the effect of an "import module" declaration is to extend the importing module's static context with the global variables (and their types) and the function signatures of the imported module. Module import is not transitive, therefore only the global variables and functions declared explicitly in the imported module are available in the importing module. Also, module import does not import schemas, therefore the importing module must explicitly import any schemas on which the imported global variables or functions depend.
The first premise below "looks up" the static context of the imported module, as defined in [5.2 Module Declaration], then extends the input static context with the global variables and function signatures declared in the imported static context.
|
||||
|
||||
|
Note that the rule above and the rules for processing a library module in [5.2 Module Declaration] above are mutually recursive.
During dynamic context processing, the effect of an "import module" declaration is to extend the importing module's dynamic context with the global variables and the function definitions of the imported module. Each variable and function name is mapped to the special value #IMPORTED
(URI) to indicate that the variable or function is defined in the imported module with the given URI.
Notation
The rules below depend on the following auxilliary judgments.
This judgment adds each variable explicitly declared in the imported module to the importing module's dynamic variable environment.
|
|||
|
|||
|
This judgment adds each function explicitly declared in the imported module to the importing module's dynamic function environment.
|
|||
|
|||
|
The first premise below "looks up" the dynamic context of the imported module, as defined in [5.2 Module Declaration]. The auxilliary judgments =>import_variables and =>import_functions add each imported global variable and function name to the input dynamic context.
|
||||
|
||||
|
Note that the rule above and the rules for processing a library module in [5.2 Module Declaration] above are mutually recursive.
[10 (XQuery)] | NamespaceDecl |
::= | "declare" "namespace" NCName "=" URILiteral |
Core Grammar
The core grammar production for namespace declarations is:
[10 (Core)] | NamespaceDecl |
::= | "declare" "namespace" NCName "=" URILiteral |
The namespace declaration is in the Core grammar, so no normalization rules are necessary.
A namespace declaration adds a new (prefix,uri) binding in the namespace component of the static environment. All namespace declarations in the prolog are passive declarations. Namespace declaration attributes of element constructors are active declarations.
statEnv1 = statEnv + namespace(NCName => (passive, URILiteral)) | ||
|
||
|
The namespace declaration does not affect the dynamic context.
[12 (XQuery)] | DefaultNamespaceDecl |
::= | (("declare" "default" "element") | ("declare" "default" "function")) "namespace" URILiteral |
Core Grammar
The core grammar production for default namespace declarations is:
[11 (Core)] | DefaultNamespaceDecl |
::= | (("declare" "default" "element") | ("declare" "default" "function")) "namespace" URILiteral |
The default namespace declarations are in the Core grammar, so no normalization rules are necessary.
A default element namespace declaration changes the default element namespace prefix binding in the namespace component of the static environment. If the string literal is the zero-length string, the default element namespace is set to the null namespace.
statEnv1 = statEnv + default_elem_namespace(#NULL-NAMESPACE) | ||
|
||
|
|
||
|
||
|
A default function namespace declaration changes the default function namespace prefix binding in the namespace component of the static environment. If the URI literal is the zero-length string, the default function namespace is set to the null namespace.
statEnv1 = statEnv + default_function_namespace(#NULL-NAMESPACE) | ||
|
||
|
|
||
|
||
|
Note that multiple declarations of the same namespace prefix in the Prolog result in a static error. However, a declaration of a namespace in the Prolog can override a prefix that has been predeclared in the static context.
Default namespace declarations do not affect the dynamic context.
[24 (XQuery)] | VarDecl |
::= | "declare" "variable" "$" VarName TypeDeclaration? ((":=" ExprSingle) | "external") |
Core Grammar
The core grammar production for variable declarations is:
[23 (Core)] | VarDecl |
::= | "declare" "variable" "$" VarName TypeDeclaration? ((":=" ExprSingle) | "external") |
Normalization of a variable declaration normalizes the variable and its corresponding expression, if it is present.
[ declare variable VarRef as SequenceType := Expr ]PrologDecl |
== |
declare variable VarRef as SequenceType := [Expr]Expr |
If an external variable declaration does not have a type declaration it is treated as if the type declaration was item()*
.
[ declare variable VarRef external ]PrologDecl |
== |
declare variable VarRef as item()* external |
[ declare variable VarRef as SequenceType external ]PrologDecl |
== |
declare variable VarRef as SequenceType external |
A variable declaration updates the variable component of the static context by associating the given variable with a static type.
If a variable declaration does not have a type declaration but has an associated expression, then the static type of the variable is the static type of the expression.
|
||||
|
||||
|
If the variable declaration has a type declaration, the static type of the variable is the specified type.
|
||||
|
||||
|
To evaluate a variable declaration, its associated expression is evaluated, and the dynamic context is updated with the variable bound to the resulting value.
|
||||
|
||||
|
Dynamic evaluation does not apply to externally defined variables. The evaluation environment must provide the values of external variables in the initial dynamic context (dynEnvDefault).
Introduction
User-defined functions specify the name of the function, the names and types of the parameters, and the type of the result. The function body defines how the result of the function is computed from its parameters.
[26 (XQuery)] | FunctionDecl |
::= | "declare" "function" QName "(" ParamList? (")" | (")" "as" SequenceType)) (EnclosedExpr | "external") |
[27 (XQuery)] | ParamList |
::= | Param ("," Param)* |
[28 (XQuery)] | Param |
::= | "$" VarName TypeDeclaration? |
Core Grammar
The core grammar productions for function declarations are:
[25 (Core)] | FunctionDecl |
::= | "declare" "function" QName "(" ParamList? (")" | (")" "as" SequenceType)) (EnclosedExpr | "external") |
[26 (Core)] | ParamList |
::= | Param ("," Param)* |
[27 (Core)] | Param |
::= | "$" VarName TypeDeclaration? |
Notation
The following auxiliary mapping rule is used for the normalization of parameters in function declarations: []Param.
Parameters without a declared typed are given the item* sequence type.
The parameter list and body of a user-defined function are all normalized into Core expressions.
[ declare function QName ( ParamList? ) as SequenceType EnclosedExpr ]PrologDecl |
== |
declare function QName ( [ParamList?]Param ) as SequenceType [EnclosedExpr]Expr |
If the return type of the function is not provided, it is given the item*
sequence type.
[declare function QName ( ParamList? ) EnclosedExpr ]PrologDecl |
== |
declare function QName( [ParamList?]Param ) as item* [EnclosedExpr]Expr |
Externally defined functions are normalized similarly.
[ declare function QName ( ParamList? ) as SequenceType external]PrologDecl |
== |
declare function QName( [ParamList?]Param ) as SequenceType external |
[declare function QName ( ParamList? ) external ]PrologDecl |
== |
declare function [QName] ( [ParamList?]Param ) as item* external |
Because functions are mutually referential, all function signatures must be defined in the static environment before static type analysis is applied to the function bodies. This rule also updates the local functions component of the static context to indicate the function is declared within the given module.
|
||||
|
||||
statEnv |- FunctionDecl =>stat statEnv1 |
Note that the static context processing is performing type checking of the function, as defined below. Note also that the type checking is done in the new environment in which the function declaration has been added which ensures that recursive calls are type-checked properly.
The static typing rules for function bodies follows normalization and processing of the static context. The typing rules below constructs a new environment in which each variable has the given expected type, then the static type of the function's body is computed under the new environment. The function body's type must be a subtype of the expected return type. If type checking fails, a static error is raised. Otherwise, static typing of the function has no other effect, as function signatures are already inside the static environment.
|
||||||||||
|
||||||||||
statEnv |- declare function QName (VarRef1 as SequenceType1, ···, VarRefn as SequenceTypen) as SequenceTyper { Expr } : Typer |
The bodies of external functions are not available and therefore cannot by type checked. To ensure type soundness, the evaluation environment must guarantee that the value returned by the external function matches the expected return type.
|
||
|
||
statEnv |- declare function QName ( VarRef1 as SequenceType1 , ···, VarRefn as SequenceTypen ) as SequenceTyper external : Typer |
A function declaration updates the dynamic context. The function name with arity N is associated with the given function body. The number of arguments is required, because XQuery permits overloading of function names as long as each function signature has a different number of arguments.
|
|||||||
|
|||||||
dynEnv |- declare function QName ( VarRef1 as SequenceType1, ···, VarRefn as SequenceTypen ) as SequenceTyper { Expr } =>dyn dynEnv1 |
An external function declaration does not affect the dynamic environment. The evaluation environment must provide the implementation for externally defined functions.
|
dynEnv |- declare function QName ( Variable1 as SequenceType1, ···, Variablen as SequenceTypen ) as SequenceTyper external =>dyn dynEnv |
The dynamic semantics of a function body are applied when the function is called and is described in [4.1.5 Function Calls].
[13 (XQuery)] | OptionDecl |
::= | "declare" "option" QName StringLiteral |
Core Grammar
The core grammar production for option declarations is:
[12 (Core)] | OptionDecl |
::= | "declare" "option" QName StringLiteral |
The XQuery Formal Semantics is intended primarily as a component that can be used by [XQuery 1.0: A Query Language for XML], or a host language of [XML Path Language (XPath) 2.0]. Therefore, the XQuery Formal Semantics relies on specifications that use it (such as [XPath 2.0], [XSLT 2.0], and [XQuery]) to specify conformance criteria in their respective environments. Specifications that set conformance criteria for their use of the formal semantics must not relax the constraints expressed in this specification.
This specification normatively defines the static typing feature which can be used in [XQuery 1.0: A Query Language for XML] or a host language of [XML Path Language (XPath) 2.0]. The static typing feature is specified using the static typing judgment introduced in [3.2.3 Static typing judgment].
In some cases, the static typing rules are not very precise (see, for example, the type inference rules for the ancestor axes—parent, ancestor, and ancestor-or-self—and for the function fn:root
). If an implementation supports a static typing extension, it must always provide a more precise type than the one defined in this specification.
This constraint is formally expressed as follows. A static typing extension Expr :ext Type must be such that for every expression Expr the following holds.
Note:
It is not recommended for a static typing extension to change the static typing behavior of expressions that specify a type explicitely (treat as
, cast as
, typeswitch
, function parameters, and type declarations in variable bindings), since the purpose of those expressions is to impose a specific type.
This section defines the auxilliary functions required to define the formal semantics of [XPath/XQuery], and gives special normalization and static typing rules for some functions in [Functions and Operators].
Introduction
This section gives the definition and semantics of functions that are used in the formal semantics but are not in [Functions and Operators]. Their dynamic semantics are defined in the same informal style as in the [Functions and Operators] document. The static semantics of some formal-semantics functions require custom typing rules.
minus
, fs:plus
, fs:times
, fs:idiv
, fs:div
, and fs:mod
These functions are overloaded placeholders with signatures and semantics as specified in the table in Appendix [B.2 Mapping of Overloaded Internal Functions].
eq
, fs:ne
, fs:lt
, fs:le
, fs:gt
, and fs:ge
These functions are overloaded placeholders with signatures and semantics as specified in the table of Appendix [B.2 Mapping of Overloaded Internal Functions].
convert-operand
functionfs:convert-operand
($actual
as
item?
, $expected
as
xdt:anyAtomicType
) as
xdt:anyAtomicType ?
The formal-semantics function fs:convert-operand
converts the operands of arithmetic and comparison operators as follows:
If $actual
is the empty sequence, returns the empty sequence.
If $actual
is of type xdt:untypedAtomic
, then
if $expected
is of type xdt:untypedAtomic
, returns $actual
cast to xs:string
;
if $expected
is of numeric type, returns $actual
cast to xs:double
otherwise returns $actual
cast to the type of $expected
.
Otherwise, the operand is returned unchanged.
No conversion is needed for numeric (or empty) operands.
|
|||
|
|||
statEnv |- fs:convert-operand (Expr1, Expr2) : Type1 |
Pairs of untyped atomic operands are converted to strings.
|
|||
|
|||
statEnv |- fs:convert-operand (Expr1, Expr2) : xs:string · quantifier (Type1) |
When an untyped operand is paired with a numeric operand, it is converted to xs:double.
|
||||
|
||||
statEnv |- fs:convert-operand (Expr1, Expr2) : xs:double · quantifier (Type1) |
Finally, an untyped atomic operand not dealt with by the above rules is converted to the type of the other operand.
|
||||
|
||||
statEnv |- fs:convert-operand (Expr1, Expr2) : Type2 · quantifier(Type1) |
convert-simple-operand
functionfs:convert-simple-operand
($actual
as
item *
, $expected
as
xdt:anyAtomicType
) as
xdt:anyAtomicTypeAtomic *
The formal-semantics function fs:convert-simple-operand
is used to convert the value of the $actual
argument such that it matches the type of the $expected
argument (or matches a sequence of that type).
The dynamic semantics of this function are as follows:
For each item in $actual
argument that is of type xdt:untypedAtomic, that item is cast to the type of the $expected
argument, and the resulting sequence is returned.
The following static semantics rules correspond to the dynamic semantics rules given above.
distinct-doc-order
functionfs:distinct-doc-order
($nodes
as
node *
) as
node *
The fs:distinct-doc-order
function sorts its input sequence of nodes by document order and removes duplicates.
The fs:distinct-doc-order
function expects a sequence of nodes as input. The resulting type is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences].
distinct-doc-order-or-atomic-sequence
functionfs:distinct-doc-order-or-atomic-sequence
($item
as
node *
) as
item*
The fs:distinct-doc-order-or-atomic-sequence
function operates on either an homogeneous sequence of nodes or an homogeneous sequence of atomic values. If the input is a sequence of nodes, is sorts those nodes by document order and removes duplicates, using the fs:distinct-doc-order function. If it is a sequence of atomic values, it returns it unchanged.
The fs:distinct-doc-order
function expects either a sequence of nodes as input or a sequence of atomic values. The resulting type is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences].
item-sequence-to-node-sequence
functionfs:item-sequence-to-node-sequence
($items
as
item *
) as
node *
Th fs:item-sequence-to-node-sequence
function converts a sequence of item values to nodes by applying the normative rules in Section 3.7.3.1 Computed Element ConstructorsXQ.
item-sequence-to-untypedAtomic
functionIntroduction
fs:item-sequence-to-untypedAtomic
($items
as
item *
) as
xdt:untypedAtomic
The fs:item-sequence-to-untypedAtomic
function converts a sequence of item values to a string of type xdt:untypedAtomic
by applying the normative rules in Section 3.7.3.2 Computed Attribute ConstructorsXQ.
If the input of the fs:item-sequence-to-untypedAtomic
function is an empty sequence, it returns a zero-length string. Otherwise, each atomic value in the input sequence is cast into a string. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.
There are no special static typing rules for this function.
item-sequence-to-untypedAtomic-PI
functionIntroduction
fs:item-sequence-to-untypedAtomic-PI
($items
as
item *
) as
xdt:untypedAtomic
The fs:item-sequence-to-untypedAtomic-PI
function converts a sequence of item values to a string of type xdt:untypedAtomic
by applying the normative rules in Section 3.7.3.5 Computed Processing Instruction ConstructorsXQ.
If the input is an empty sequence, the fs:item-sequence-to-untypedAtomic-PI
function returns a zero-length string. Otherwise, each atomic value in the input sequence is cast into a string. If any of the resulting strings contains the string "?>", a dynamic error is raised. 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.
Leading whitespace is removed from the resulting string.
There are no special static typing rules for this function.
item-sequence-to-untypedAtomic-text
functionIntroduction
fs:item-sequence-to-untypedAtomic-text
($items
as
item *
) as
xdt:untypedAtomic?
The fs:item-sequence-to-untypedAtomic-text
function converts a sequence of item values to a string of type xdt:untypedAtomic
, or empty, by applying the rules in Section 3.7.3.4 Text Node ConstructorsXQ.
If the input is the empty sequence, the fs:item-sequence-to-untypedAtomic-text
function returns the empty sequence. Otherwise, each atomic value in the input sequence is cast into a string. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.
There are no special static typing rules for this function.
item-sequence-to-untypedAtomic-comment
functionIntroduction
fs:item-sequence-to-untypedAtomic-comment
($items
as
item *
) as
xdt:untypedAtomic
The fs:item-sequence-to-untypedAtomic-comment
function converts a sequence of item values to a string of type xdt:untypedAtomic
by applying the normative rules in Section 3.7.3.6 Computed Comment ConstructorsXQ.
If the input is the empty sequence, the fs:item-sequence-to-untypedAtomic-comment
function returns a zero-length string. Otherwise, each atomic value in the input sequence is cast into a string. 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. It is a dynamic error if the result of the content expression of a computed
comment constructor contains two adjacent hyphens or ends with a hyphen.
There are no special static typing rules for this function.
apply-ordering-mode
functionfs:apply-ordering-mode
($items
as
item()*
) as
item()*
If the statEnv.orderingMode is set to ordered, the fs:apply-ordering-mode
function is the identity function, returning its input sequence in its original order.
statEnv.orderingMode = ordered dynEnv |- Expr => Value |
|
dynEnv |- fs:apply-ordering-mode (Expr) => Value |
If the statEnv.orderingMode is set to unordered, the fs:apply-ordering-mode
is equivalent to the fn:unordered
function, returning the items from its input sequence in arbitrary order.
statEnv.orderingMode = ordered dynEnv |- fn:unordered (Expr) => Value |
|
dynEnv |- fs:apply-ordering-mode (Expr) => Value |
If the ordering context is set to ordered
, the static type of the input expression of the fs:apply-ordering-mode
function is left unchanged.
statEnv.orderingMode = ordered |
|
statEnv |- fs:apply-ordering-mode (Expr) : Type |
If the ordering context is set to unordered
, the static type of the input expression of the fs:apply-ordering-mode
function is computed using the prime and quantifier judgments, as for the fn:unordered
function.
statEnv.orderingMode = unordered |
|
statEnv |- fs:apply-ordering-mode (Expr) : prime(Type) · quantifier(Type) |
to
functionfs:to
($firstval
as
xs:integer?
, $lastval
as
xs:integer?
) as
xs:integer*
The formal semantics function fs:to
is a wrapper function for the op:to
operator, taking the semantics of the range expression over empty sequences into account.
If one of the input paramter for fs:to
is the empty sequence, the function returns the empty sequence, otherwise it returns the result of calling the op:to
operator. This semantics is equivalent to the following function call.
declare function fs:to($firstval as xs:integer?, $lastval as xs:integer?) as xs:integer* { if (fn:empty($lastval) or fn:empty($lastval) then () else op:to($firstval,$lastval) };
The static type of fs:to
does not require any additional static typing rule, and is typed as a function call based on the above signature.
Introduction
This section gives special normalization and static typing rules for functions in [Functions and Operators] for which the standard normalization of typing rules are not appropriate. All functions that are not mentioned behave as described in Section [4.1.5 Function Calls]. When given, the static typing rules in this section always give more precise type information than the generic rule based on the function's signature.
fn:last
context functionAs explained in [3.1.2 Dynamic Context], the fn:last()
context function is modeled using the Formal Semantics variable $
fs:last
.
fn:position
context functionAs explained in [3.1.2 Dynamic Context], the fn:position()
context function is modeled using the Formal Semantics variable $
fs:position
.
[fn:position ()]Expr |
== |
$ fs:position |
fn:abs
, fn:ceiling
, fn:floor
, fn:round
, and fn:round-half-to-even
functionsThe typing rules for the fn:abs
, fn:ceiling
, fn:floor
, fn:round
, and fn:round-half-to-even
functions promote their input type to the (least) base primitive numeric type from which the input type is derived. Parameters of type xdt:untypedAtomic
are always promoted to xs:double
. Instead of writing a separate judgment for each function, we write one rule with function variable
F, which is one of the fn:abs
, fn:ceiling
, fn:floor
, fn:round
, or fn:round-half-to-even
functions.
fn:boolean
functionThe fn:boolean
function as described in the [Functions and Operators] document takes an empty sequence, a sequence of one or more nodes, or a singleton value of type xs:string
, xdt:untypedAtomic
or some numeric type. All other values are illegal.
fn:collection
and fn:doc
functionsThe fn:collection
function as described in the [Functions and Operators] document, takes a string-valued expression, which denotes a URI, and returns a value.
If the fn:collection
function has no parameter, the result type is given by the implementation for the default sequence if it exists.
If the argument to fn:collection
is a StringLiteral expression and that string is defined in statEnv.collectionType, then the result type is the type corresponding to the StringLiteral in statEnv.collectionType.
Otherwise, if the argument is not a literal string or is a string but not defined in statEnv.collectionType, then we don't know anything about the URI, and the static type is a collection of nodes:
statEnv.collectionType(StringLiteral) undefined |
|
statEnv |- fn:collection (Expr) : (element | attribute | processing-intruction | text | comment | document ) * |
statEnv |- Expr is not a StringLiteral |
|
statEnv |- fn:collection (Expr) : (element | attribute | processing-intruction | text | comment | document ) * |
The static type of the fn:doc
function has similar static rules, but, in addition, requires that the static type of the URI be any document:
|
|||
|
|||
statEnv |- fn:doc (StringLiteral) : Type |
Otherwise, if the argument is not a literal string or is not defined in the domain of statEnv.docType, then we don't know anything about the URI, and the static type is document:
fn:data
functionIntroduction
The fn:data
function converts a sequence of items to a sequence of atomic values.
Notation
Infering the type for the fn:data
function is done by applying the data on auxiliary judgment, using the same approach as for the XPath steps.
The general rule for fn:data
is to apply the filter data on to the prime type of its argument type, then apply the quantifier to the result:
|
|||
|
|||
statEnv |- fn:data (Expr) : Type1 · quantifier(Type) |
When applied to none, data on yields none.
When applied to empty, data on yields empty.
When applied to the union of two types, data on is applied to each of the two types. The resulting type is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences]. This rule is necessary because data on may return a sequence of atomic types.
|
|||
|
|||
statEnv |- data on (Type1|Type2) : prime(Type1'|Type2') · quantifier(Type1'|Type2') |
When applied to an atomic type, data on simply returns the atomic type:
When applied to comment or processing instruction node types, data on returns xs:string
When applied to text, and document node types, data on returns xdt:untypedAtomic
When applied to element node types with type annotationXQ xdt:untyped
, the data on filter returns xdt:untypedAtomic
.
|
||
|
||
statEnv |- data on ElementType : xdt:untypedAtomic |
When applied to an attribute node type, the data on filter returns the attribute's simple type.
|
|||
|
|||
statEnv |- data on AttributeType : Type |
When applied to an element type whose type annotationXQ denotes a simple type or a complex type of simple content, data on returns the element's simple type.
|
||||
|
||||
statEnv |- data on ElementType : Type1 |
When applied to an element type whose type annotationXQ denotes a complex type of mixed content, the data on filter returns xdt:untypedAtomic
.
|
|||
|
|||
statEnv |- data on ElementType : xdt:untypedAtomic |
The data on filter is not defined on any element type whose type annotationXQ denotes a complex type of complex content and therefore apply data on to such a node raises a static error.
Example
Consider the following variables and its corresponding static type.
$x : (element price { attribute currency { xs:string }, xs:decimal } | element price_code { xs:integer })
Applying the fn:data
function on that variable results in the following type.
fn:data($x) : (xs:decimal | xs:integer)
Because the input type is a choice, applying the data on filter results in a choice of simple types for the output of the fn:data
function.
fn:distinct-values
functionThe fn:distinct-values
function expects a sequence of atomic values as input and returns a sequence of prime types, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences].
fn:unordered
functionThe static semantics for unordered is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences]. The type of each argument is determined, and then prime(.) and quantifier(.) are applied to the sequence type (Type1, Type2).
fn:min
, fn:max
, fn:avg
, and fn:sum
functionsIntroduction
The dynamic evaluation rules for aggregate functions convert any item of type xdt:untypedAtomic
in the input sequence to xs:double
, then attempt to promote all values in the input sequence to values that are comparable. The static typing rules reflect the dynamic rules.
The fn:sum
function has two forms. The first form takes two arguments: The first argument is the input sequence and the second argument is the value that should be returned if the input sequence is empty. In case there is no second argument, the value returned for an empty sequence is the xs:integer
value 0.
Notation
The type function convert_untypedAtomic takes a prime type and converts all occurrences of the type xdt:untypedAtomic
to a target type. It is defined by induction as follows.
convert_untypedAtomic(xdt:untypedAtomic , Type) |
= | Type |
convert_untypedAtomic(FormalItemType, Type) | = | FormalItemType (FormalItemType is not xdt:untypedAtomic ) |
convert_untypedAtomic(empty , Type) |
= | empty |
convert_untypedAtomic(none , Type) |
= | none |
convert_untypedAtomic(Type1 | Type2, Type) | = | convert_untypedAtomic(Type1, Type) | convert_untypedAtomic(Type2, Type) |
Notation
The function aggregate_quantifier converts the input type quantifier zero-or-more or zero-or-one to the result type quantifier zero-or-one, and converts the input type quantifier one or one-or-more, to the result type quantifier one.
aggregate_quantifier(? ) |
= | ? |
aggregate_quantifier(* ) |
= | ? |
aggregate_quantifier(1 ) |
= | 1 |
aggregate_quantifier(+ ) |
= | 1 |
Now we can define the static typing rules for the aggregate functions. First, the input type is converted to a prime type. Second, the type function convert_untypedAtomic is applied to the prime type, yielding a new prime type, in which occurrences of xdt:untypedAtomic
are converted to xs:double
. Third, the judgment can be
promoted to is applied to the new prime type and target type. The result type is combined with the aggregate quantifier of the input type.
For a given aggregate function, instead of writing a separate judgment for each target type, we write one rule using a target type Type0.
For fn:min
and fn:max
, the target type Type0 is either xs:string
, xs:integer
, xs:decimal
, xs:float
, xs:double
, xs:date
, xs:time
, xs:dateTime
, xdt:yearMonthDuration
, or xdt:dayTimeDuration
.
|
|||||||
|
|||||||
statEnv |- fn:min (Expr) : Type0 · aggregate_quantifier(quantifier(Type)) |
|
|||||||
|
|||||||
statEnv |- fn:max (Expr) : Type0 · aggregate_quantifier(quantifier(Type)) |
For fn:avg
, the target type Type is either xs:decimal
, xs:float
, xs:double
, xdt:yearMonthDuration
, or xdt:dayTimeDuration
.
|
|||||||
|
|||||||
statEnv |- fn:avg (Expr) : Type0 · aggregate_quantifier(quantifier(Type)) |
For fn:sum
, the target type Type is either xs:integer
, xs:decimal
, xs:float
, xs:double
, xdt:yearMonthDuration
, or xdt:dayTimeDuration
. The second argument in fn:sum
is the value that should be returned if the input sequence is empty. The result type is the union of the target type and the type of the
second argument.
|
|||||||||
|
|||||||||
statEnv |- fn:sum (Expr1,Expr2) : Type0 · aggregate_quantifier(quantifier(Type1)) | Type2 |
fn:remove
functionThe static type for the fn:remove
function is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences]. Since one item may be removed from the sequence, the resulting type is made optional.
fn:reverse
functionThe static type for the fn:reverse
function is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences].
fn:subsequence
functionThe fn:subsequence
function has special typing rules when its second argument is the numeric literal value 1 or the built-in variable $
fs:last
. These rules provide better typing for path expressions such as Expr[1] and Expr[fn:last
()].
If the type of the input expression has exactly one or one-or-more items, then the type inferred for fn:subsequence
is the prime type of the input type.
|
||
|
||
|
The same rule applies when the last item in the input sequence is selected.
|
||
|
||
|
If the type of the input expression has zero or more items, then fn:subsequence
, when selecting the first item, has zero-or-one of the prime type of the input type.
|
||
|
||
|
The same rule applies when the last item in the input sequence is selected.
|
||
|
||
|
The last rule applies to all other applications of the fn:subsequence
function.
op:union
, op:intersect
, and op:except
operatorsThe static semantics for op:union
is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences]. The type of each argument is determined, and then prime(.) and quantifier(.) are applied to the sequence type (Type1, Type2).
|
||
|
||
|
The static semantics of op:intersect
is analogous to that for op:union
. Because an intersection may be empty, the result type is optional.
|
|||
|
|||
|
The static semantics of op:except
follows. The type of the second argument is ignored as it does not contribute to the result type. As with op:intersect
, the result of op:except
may be the empty sequence.
fn:insert-before
functionThe static type for the fn:insert-before
function is computed using prime and quantifier, which are defined in [8.4 Judgments for FLWOR and other expressions on sequences].
fn:zero-or-one
, fn:one-or-more
, and fn:exactly-one
functionsThe functions fn:zero-or-one
, fn:one-or-more
, and fn:exactly-one
check that the cardinality of a sequence is in the expected range. They are useful to override the static type inferred for a given query. For example, in the following query, the user may know that all ISBN numbers are unique and therefore that the function always return at most one book element. However, the static typing feature cannot infers a precise enough type and will return a static type
error at compile time.
declare function book_with_isbn($isbn as xs:string) as schema-element(book)? { //book[@isbn=$isbn] }
In that query, the fn:zero-or-one
function can be used to tell the type system that the cardinality is known to be zero or one.
declare function book_with_isbn($isbn as xs:string) as schema-element(book)? { fn:zero-or-one(//book[@isbn=$isbn]) }
The static typing rules