attributes"> base-uri"> children"> content"> namespaces"> nilled"> node-name"> parent"> prefix"> string-value"> target"> type-name"> uri"> string-value"> typed-value"> ]>
XQuery 1.0 and XPath 2.0 Data Model &doc.prefix;-&doc.date; W3C Working Draft &date.day; &date.month; &date.year; &url.this; XML http://www.w3.org/TR/xpath-datamodel/ http://www.w3.org/TR/2003/WD-xpath-datamodel-20031112/ http://www.w3.org/TR/2003/WD-xpath-datamodel-20030502/ Mary Fernández (XML Query WG) AT&T Labs mff@research.att.com Ashok Malhotra (XML Query and XSL WGs) Microsoft ashokma@microsoft.com Jonathan Marsh (XSL WG) Microsoft jmarsh@microsoft.com Marton Nagy (XML Query WG) Science Applications International Corporation (SAIC) marton.nagy@saic.com Norman Walsh (XSL WG) Sun Microsystems Norman.Walsh@Sun.COM

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 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.

The XQuery 1.0 and XPath 2.0 Data Model has been defined jointly by the XML Query Working Group and the XSL Working Group (both part of the XML Activity).

This working draft includes a number of changes made in response to comments received during the Last Call period that ended on Feb. 15, 2004. The working group is continuing to process these comments, and additional changes are expected.

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

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

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

This document defines the W3C XQuery 1.0 and XPath 2.0 Data Model, which is the data model of , , and , and any other specifications that reference it. This data model is based on the data model and earlier work on an . This document is the result of joint work by the and the .

 English

See the CVS changelog.
Introduction

This document defines the XQuery 1.0 and XPath 2.0 Data Model, which is the data model of , and

The XQuery 1.0 and XPath 2.0 Data Model (henceforth "data model") serves two purposes. First, it defines the information contained in the input to an XSLT or XQuery processor. Second, it defines all permissible values of expressions in the XSLT, XQuery, and XPath languages. A language is closed with respect to a data model if the value of every expression in the language is guaranteed to be in the data model. XSLT 2.0, XQuery 1.0, and XPath 2.0 are all closed with respect to the data model.

The data model is based on the (henceforth "Infoset"), but it requires the following new features to meet the and :

Support for XML Schema types. The XML Schema recommendations define features, such as structures () and simple data types (), that extend the XML Information Set with precise type information.

Representation of collections of documents and of complex values. ()

As with the Infoset, the XQuery 1.0 and XPath 2.0 Data Model specifies what information in the documents is accessible, but it does not specify the programming-language interfaces or bindings used to represent or access the data.

The data model can represent various values including not only the input and the output of a stylesheet or query, but all values of expressions used during the intermediate calculations. Examples include the input document or document repository (represented as a &documentNode; or a sequence of &documentNode;s), the result of a path expression (represented as a sequence of nodes), the result of an arithmetic or a logical expression (represented as an atomic value), a sequence expression resulting in a sequence of items, etc.

This document provides a precise definition of the properties of nodes in the XQuery 1.0 and XPath 2.0 Data Model, how they are accessed, and how they relate to values in the Infoset and PSVI.

 Concepts

This section outlines a number of general concepts that apply throughout this specification.

Terminology

For a full glossary of terms, see .

In this specification the words must, must not, should, should not, may and recommended are to be interpreted as described in .

This specification distinguishes between the data model as a general concept and specific items (documents, elements, atomic values, etc.) that are concrete examples of the data model by identifying all concrete examples as instances of the data model.

Every instance of the data model is a sequence..

A sequence is an ordered collection of zero or more items. A sequence cannot be a member of a sequence. A single item appearing on its own is modeled as a sequence containing one item. Sequences are defined in .

An item is either a node or an atomic value,

Every node is one of the seven kinds of nodes defined in . Nodes form a tree that consists of a root node plus all the nodes that are reachable directly or indirectly from the root node via the children, attributes, and namespaces accessors. Every node belongs to exactly one tree, and every tree has exactly one root node.

A tree whose root node is a &documentNode; is referred to as a document.

A tree whose root node is not a &documentNode; is referred to as a fragment.

An atomic value is a value in the value space of an atomic type and is labeled with the name of that atomic type.

An atomic type is a primitive simple type or a type derived by restriction from another atomic type. (Types derived by list or union are not atomic.)

There are 24 primitive simple types: the 19 defined in of and xdt:anyAtomicType, xdt:untyped, xdt:untypedAtomic, xdt:dayTimeDuration, and xdt:yearMonthDuration, defined in .

A type is represented in the data model by an expanded-QName.

An expanded-QName is a pair of values consisting of a possibly empty namespace URI and a local name. They belong to the value space of the XML Schema type xs:QName. References to xs:QName in this document always mean the value space, i.e. a namespace URI, local name pair (and not the lexical space referring to constructs of the form “prefix:local-name”).

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

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.

In all cases where this specification leaves the behavior implementation-defined or implementation-dependent, the implementation has the option of providing mechanisms that allow the user to influence the behavior.

This document normatively defines the XQuery 1.0 and XPath 2.0 Data Model. In this document, examples and material labeled as "Note" are provided for explanatory purposes and are not normative.

 Notation

In addition to prose, this specification defines a set of accessor functions to explain the data model. The accessors are shown with the prefix dm:. This prefix is always shown in italics to emphasize that these functions are abstract; they exist to explain the interface between the data model and specifications that rely on the data model: they are not accessible directly from the host language.

Several prefixes are used throughout this document for notational convenience. The following bindings are assumed.

xs: bound to http://www.w3.org/2001/XMLSchema

xsi: bound to http://www.w3.org/2001/XMLSchema-instance

xdt: bound to http://www.w3.org/&date.year;/&date.MM;/xpath-datatypes

fn: bound to http://www.w3.org/2004/07/xpath-functions

In practice, any prefix that is bound to the appropriate URI may be used.

The signature of accessor functions is shown using the same style as , described in .

This document relies on the and PSVI. Information items and properties are indicated by the styles information item and infoset property, respectively.

Some aspects of type assignment rely on the ability to access properties of the schema components. Such properties are indicated by the style {component property}. Note that this does not mean a lightweight schema processor cannot be used, it only means that the application must have some mechanism to access the necessary properties.

 Node Identity

Each node has a unique identity. Every node in an instance of the data model is unique: identical to itself, and not identical to any other node. (Atomic values do not have identity; every instance of the value “5” as an integer is identical to every other instance of the value “5” as an integer.)

The concept of node identity should not be confused with the concept of a unique ID, which is a unique name assigned to an element by the author to represent references using ID/IDREF correlation.

 Document Order

A document order is defined among all the nodes accessible during a given query or transformation. Document order is a total ordering, although the relative order of some nodes is implementation-dependent. Informally, document order corresponds to the order in which the first character of the XML representation of each node occurs in the XML representation of the document. Document order is stable, which means that the relative order of two nodes will not change during the processing of a given query or transformation, even if this order is implementation-dependent.

Within a tree, document order satisfies the following constraints:

The root node is the first node.

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

&namespaceNode;s immediately follow the &elementNode; with which they are associated. The relative order of &namespaceNode;s is stable but implementation-dependent.

&attributeNode;s immediately follow the &namespaceNode;s of the element with which they are associated. The relative order of &attributeNode;s is stable but implementation-dependent.

&elementNode;s occur before their children; children occur before following-siblings.

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

 Sequences

An important characteristic of the data model is that there is no distinction between an item (a node or an atomic value) and a singleton sequence containing that item. An item is equivalent to a singleton sequence containing that item and vice versa.

A sequence may contain nodes, atomic values, or any mixture of nodes and atomic values. When a node is added to a sequence its identity remains the same. Consequently a node may occur in more than one sequence and a sequence may contain duplicate items.

Sequences never contain other sequences; if sequences are combined, the result is always a “flattened” sequence. In other words, appending “(d e)” to “(a b c)” produces a sequence of length 5: “(a b c d e)”. It does not produce a sequence of length 4: “(a b c (d e))”, such a nested sequence never occurs.

Sequences replace node-sets from XPath 1.0. In XPath 1.0, node-sets do not contain duplicates. In generalizing node-sets to sequences in XPath 2.0, duplicate removal is provided by functions on node sequences.

 Types

The data model supports strongly typed language such as and that have a type system based on . The type system is formally defined in .

Every item in the data model has both a value and a type. In addition to nodes, the data model can represent atomic values like the number 5 or the string “Hello World.” For each of these atomic values, the data model contains both the value of the item (such as 5 or “Hello World”) and its type name (such as xs:integer or xs:string).

Representation of Types

The data model uses expanded-QNames to represent the names of schema types, which include the built-in types defined by , five additional types defined by this specification, and may include other user- or implementation-defined types.

For XML Schema types, the namespace name of the expanded-QName is the target namespace property of the type definition, and its local name is the name property of the type definition.

The data model relies on the fact that an expanded-QName uniquely identifies every named type. (Although it is possible for different schemas to define different types with the same expanded-QName, at most one of them can be used in any given validation episode.)

For anonymous types, the processor must construct an anonymous type name that is distinct from the name of every named type and the name of every other anonymous type. An anonymous type name is an implementation defined, unique type name provided by the processor for every anonymous type declared in the schemas available in the static context. Anonymous type names must be globally unique across all anonymous types that are accessible to the processor. In the formalism of this specification, the anonymous type names are assumed to be xs:QNames, but in practice implementations are not required to use xs:QNames to represent the implementation-defined names of anonymous types.

The scope over which the names of anonymous types must be meaningful and distinct depends on the processing context. In XSLT, it is the duration of an entire transformation. In XQuery, it is the duration of the evaluation of a top-level expression, i.e. an expression not contained in any other expression.

The data model associates schema type information with &elementNode;s, &attributeNode;s and atomic values. The item is guaranteed to be an instance of that kind of item with the given schema type.

The data model does not represent element or attribute declaration schema components, but it supports various type-related operations. The semantics of other operations, for example, checking if a particular instance of an &elementNode; has a given schema type is defined in .

Predefined Types

In addition to the 19 types defined in of , the data model defines five additional types: xdt:anyAtomicType, xdt:untyped, xdt:untypedAtomic, xdt:dayTimeDuration, and xdt:yearMonthDuration:

The abstract datatype xdt:anyAtomicType is a child of xs:anySimpleType and is the base type for all the primitive atomic types described in . This datatype cannot be used in type declarations, nor can it be used as a base for user-defined atomic types. It can be used, as discussed in , to define a required type (for example in a function signature) to indicate that any of the primitive atomic types or xdt:untypedAtomic is acceptable.

The datatype xdt:untyped is a child of xs:anyType and serves as a special type annotation to indicate types that have not been validated by a XML Schema or a DTD. This type cannot be used in type declarations, nor can it be used as a base for user-defined types. It can be used, as discussed in , to define a required type (for example in a function signature) to indicate that only an untyped value is acceptable.

The datatype xdt:untypedAtomic is a child of xdt:anyAtomicType and serves as a special type annotation to indicate atomic values that have not been validated by a XML Schema or a DTD or have received an instance type annotation of xs:anySimpleType in the PSVI. This datatype cannot be used in type declarations, nor can it be used as a base for user-defined atomic types. It can be used, as discussed in , to define a required type (for example in a function signature) to indicate that only an untyped atomic value is acceptable.

The type xdt:dayTimeDuration is derived from xs:duration by restricting its lexical representation to contain only the days, hours, minutes and seconds components. The value space of xdt:dayTimeDuration is the set of fractional second values. The components of xdt:dayTimeDuration correspond to the day, hour, minute and second components defined in Section 5.5.3.2 of , respectively. xdt:dayTimeDuration is derived from xs:duration as follows:

]]>

To make the long pattern easier to read, it has been formatted on six lines using additional new line and space characters in the pattern string. These additional characters should not be interpreted as part of the pattern.

The type xdt:yearMonthDuration is derived from xs:duration by restricting its lexical representation to contain only the year and month components. The value space of xdt:yearMonthDuration is the set of xs:integer month values. The year and month components of xdt:yearMonthDuration correspond to the Gregorian year and month components defined in section 5.5.3.2 of , respectively.

The type xdt:yearMonthDuration is derived from xs:duration as follows:

]]> Type Hierarchy

The diagram below shows how the nodes, primitive simple types, and user defined types fit together into a hierarchy.

The xs:IDREFS, xs:NMTOKENS, xs:ENTITIES and user-defined list and union types are special types in that these types are lists or unions rather than true subtypes.

 Atomic Values

An atomic value can be constructed from a lexical representation. Given a string and an atomic type, the atomic value is constructed in such a way as to be consistent with validation. If the string does not represent a valid value of the type, an error is raised. When xdt:untypedAtomic is specified as the type, no validation takes place. The details of the construction are described in and the related section of .

String Values

A string value can be constructed from an atomic value. Such a value is constructed by converting the atomic value to its string representation as described in . Using the canonical lexical representation for atomic values may not always be compatible with XPath 1.0. These and other backwards incompatibilities are described in .

 Data Model Construction

This section describes the constraints on instances of the data model.

The data model supports well-formed XML documents conforming to or . Documents that are not well-formed are, by definition, not XML. XML documents that do not conform to or are not supported (nor are they supported by ).

In other words, the data model supports the following classes of XML documents:

Well-formed documents conforming to or .

DTD-valid documents conforming to or , and

W3C XML Schema-validated documents.

This document describes how to construct an instance of the data model from an or a Post Schema Validation Infoset (PSVI), the augmented infoset produced by an XML Schema validation episode.

An instance of the data model can also be constructed directly through application APIs, or from non-XML sources such as relational tables in a database.

The data model supports some kinds of values that are not supported by . Examples of these are document fragments and sequences of &documentNode;s. The data model also supports values that are not nodes. Examples of these are sequences of atomic values, or sequences mixing nodes and atomic values. These are necessary to be able to represent the results of intermediate expressions in the data model during expression processing.

Direct Construction

Although this document describes construction of an instance of the data model in terms of infoset properties, an infoset is not an absolutely necessary precondition for building an instance of the data model.

There are no constraints on how an instance of the data model may be constructed directly, save that the resulting instance must satisfy all of the constraints described in this document.

 Construction from an Infoset

An instance of the data model can be constructed from an that satisfies the following general constraints:

All general and external parsed entities must be fully expanded. The Infoset must not contain any unexpanded entity reference information items.

The infoset must provide all of the properties identified as required in this document. The properties identified as optional may be used, if they are present. All other properties are ignored.

An instance of the data model constructed from an information set must be consistent with the description provided for each node kind.

 Construction from a PSVI

An instance of the data model can be constructed from a PSVI, whose element and attribute information items have been strictly assessed, laxly assessed, or have not been assessed. Constructing an instance of the data model from a PSVI must be consistent with the description provided in this section and with the description provided for each node kind.

Data model construction requires that the PSVI provide unique names for all anonymous schema types.

does not require all schema processors to provide unique names for anonymous schema types. In order to build an instance of the data model from a PSVI produced by a processor that does not provide the names, some post-processing will be required in order to assure that they are all uniquely identified before construction begins.

An incompletely validated document is an XML document that has a corresponding schema but whose schema-validity assessment has resulted in one or more element or attribute information items being assigned values other than 'valid' for the validity property in the PSVI.

The data model supports incompletely validated documents. Elements and attributes that are not valid are treated as having unknown schema types.

The most significant difference between Infoset construction and PSVI construction occurs in the area of schema type assignment. Other differences can also arise from schema processing: default attribute and element values may be provided, white space normalization of element content may occur, and the user-supplied lexical form of elements and attributes with atomic schema types may be lost.

Mapping PSVI Additions to Type Names

A PSVI element or attribute information item may have a validity property. The validity property may be valid, invalid, or notKnown and reflects the outcome of schema-validity assessment. In the data model, precise schema type information is exposed for Element and &attributeNode;s that are valid. Nodes that are not valid are treated as if they were simply well-formed XML and only very general schema type information is associated with them.

Element and Attribute Node Type Names

The precise definition of the schema type of an element or attribute information item depends on the properties of the PSVI. In the PSVI, only guarantees the existence of either the type definition property, or the type definition namespace, type definition name and type definition anonymous properties. If the type definition refers to a union type, there are further properties defined, that refer to the type definition which actually validated the item's normalized value. These properties are not used to determine the schema type of the node.

If the validity and validation attempted properties exist and have the values valid and full, respectively, the schema type of an element or attribute information item is represented by an expanded-QName whose namespace and local name correspond to the first applicable items in the following list:

If the type definition property exists:

If the {name} property is not absent, the {target namespace} and {name} properties of the type definition property;

Otherwise, the namespace and local name of the appropriate anonymous type name.

If type definition anonymous exists:

If it is false: the type definition namespace and the type definition name properties;

Otherwise, the namespace and local name of the appropriate anonymous type name.

If the validity property does not exist or is not valid, or the validition attempted property does not exist or is not full, the schema type of an element is xdt:untyped and the type of an attribute is xdt:untypedAtomic.

 Atomic Value Type Names

The typed value of &attributeNode;s and some &elementNode;s is an atomic value. (Elements that have a complex type with element-only content do not contain atomic values; such nodes have no typed value and this section does not apply to them.)

The schema type of each item in the typed value of an Element or &attributeNode; depends on the schema type of the node and may be further refined. The type must be further refined when the Element or &attributeNode; has a list or union type.

If the schema type definition of a node refers to a union type, the PSVI will contain properties that refer to the type definition which actually validated the item's normalized value. These properties are either the member type definition, or the member type definition namespace, member type definition name and member type definition anonymous properties. If these are available, the schema type of the typed value of an element or attribute will be the member type that actually validated the schema normalized value.

The schema type of the typed value is represented by an expanded-QName whose namespace and local name correspond to the first applicable items in the following list:

If the schema type of the node (as defined in ) is xdt:untyped or xdt:untypedAtomic, the namespace and local name of xdt:untypedAtomic.

If member type definition exists:

If the {name} property is not absent, the {target namespace} and {name} properties of the member type definition property;

Otherwise, the namespace and local name of the appropriate anonymous type name.

If member type definition anonymous exists:

If it is false: the member type definition namespace and the member type definition name properties;

Otherwise, the namespace and local name of the appropriate anonymous type name.

Otherwise, the namespace and local name of the node’s schema type.

The {variety} of the resulting type will be either atomic or list. If the {variety} is atomic, that is the type of the atomic value.

If the {variety} is list, each member of the list must be examined to determine its atomic value. The schema normalized value of the node is a space-separated list of lexical forms. These lexical forms can be used to create a list of strings, where each string represents one member of the list of atomic values.

For each string in the list, the nominal type of each member of the list is identified by the {item type definition} of the type identified above.

If the {variety} of the nominal type is atomic, if the string is castable to that type, then the atomic value is the result of casting the string to that type.

If the {variety} of the nominal type is union, then each type listed in the {member type definitions} must be considered in turn as a nominal type.

If the {variety} of the nominal type is list, then the {item type definition} must be considered as the nominal type.

Note that this process is recursive: the member type of a union may be a list which may have an item type that is a union. The process is guaranteed to terminate because (1) it terminates immediately if the initial {variety} is atomic and (2) the initial {variety} can only be non-atomic if validation succeeded.

 Mapping xsi:nil on &elementNode;s

introduced a mechanism for signaling that an element should be accepted as valid when it has no content despite a content type which does not require or even necessarily allow empty content. That mechanism is the xsi:nil attribute.

The data model exposes this special semantic in the &dm.prop.nilled; property. (It also exposes the attribute, irrespective of whether or not schema processing has been performed.)

If the validity property exists on an &elementNode; and is valid then if the nil property exists and is true, then &dm.prop.nilled; property is true. In all other cases, including all cases where schema validity assessment was not attempted or did not succeed, the &dm.prop.nilled; property is false.

 Dates and Times

The date and time types require special attention. The following sections apply to xs:dateTime, xs:date, and xs:time types and types derived from them.

Storing xs:dateTime, xs:date, and xs:time Values in the Data Model

permits xs:dateTime, xs:date, and xs:time values both with and without timezones and therefore only specifies a partial ordering between date and time values. In the data model, it is necessary to preserve timezone information.

In order to achieve this goal, xs:dateTime, xs:date, and xs:time values must be stored with care. If the lexical representation of the value includes a timezone, it is converted to UTC as defined by and the timezone in the lexical representation is converted to a xdt:dayTimeDuration value (as an offset from UTC). Implementations must keep track of both these values for each xs:dateTime, xs:date, and xs:time stored.

Lexical representations that do not have a timezone are assumed to be in UTC for the purposes of normalization only. An empty sequence is used for their timezone.

Thus, for the purpose of validation, 2003-01-02T11:30:00-05:00 is converted to 2003-01-02T16:30:00Z, but in the data model it must be stored as as (2003-01-02T16:30:00Z, -PT5H0M). The value 2003-01-16T16:30:00 is stored as (2003-01-16T16:30:00Z, ()) because it has no timezone.

Retreiving the Typed Value of xs:dateTime, xs:date, and xs:time Values

For xs:dateTime, xs:date and xs:time, the typed value is the atomic value that is determined from its stored form as follows:

If the timezone component is not the empty sequence (the timezone was specified), then the value contains the time component, normalized to the timezone specified by the timezone component, as well as the timezone component. The stored values "(2003-01-02T16:30:00Z, -PT5H0M)" produce the value "2003-01-02T11:30:00-05:00".

If the timezone component is the empty sequence (the timezone was not specified), then the time component without any indication of timezone. The stored values "(2003-01-02T16:30:00Z, ())" produce the value "2003-01-02T16:30:00".

 String and Typed Values

The string-value and typed-value of &documentNode;s, &elementNode;s, and &attributeNode;s are defined in terms of &dm.prop.string-value; and &dm.prop.typed-value; properties. This specification describes how values are computed for those properties when constructing an instance of the data model from an Infoset or a PSVI.

This is a formalism used to simplify the explanations in this specification, it is not a constraint on implementations. In practice, implementations are free to adopt any strategy they wish, provided that the results are indistinguishable in every significant respect from the results that would be obtained by following precisely the algorithms described in this specification.

In practice, some implementations, particularly those constructing instances of the data model from sources other than Infosets or PSVIs, may have access to only the string or typed values and not both. In order to support these implementations, this specification explicitly identifies some variations in the string value of a node as insignificant. Implementations that do not have access to, or cannot retain, the original string value of a node may reconstruct it from the typed value. In this case, the string value may differ from the string value that would be returned by an implementation that preserved the original lexical form.

Consider the following node:

<offset xsi:type="xs:integer">0030</offset>

Assuming that the node is valid, it has a typed value of “30” as an xs:integer. Some implementations will return “0030” as the string value and some will return “30”. In this regard, any string value that is a lexical representation of the typed value is acceptable.

Applications that care about the original lexical forms must choose an appropriate implementation.

Consistent with XML Schema Validation

Validity assessment only assures that the lexical forms present in the Infoset or PSVI are within the lexical space of the required schema type. So while such assessment can determine that “0030” is a valid integer, it does not produce a typed integer value.

The data model contains not only the string value of each node, it also contains the typed value. In other words, the process of constructing an instance of the data model does, in principle, require that an implementation produce the typed integer value “30” from the lexical value “0030”.

The phrase “derived from the string-value of the node and its type in a way that is consistent with XML Schema validation” is used to describe this process. It is impossible to define precisely what this means as implementations may choose different internal representations for typed values. However, it is a constraint on the data model that string values and typed values must be consistent. Although variations in string value are allowed, the string value must always be a valid lexical representation of the typed value.

Pattern Facets

Creating a subtype by restriction generally reduces the value space of the original schema type. For example, expressing a hat size as a restriction of decimal with a minimum value of 6.5 and maximum value of 8.0 creates a schema type whose legal values are only those in the range 6.5 to 8.0.

The pattern facet is different because it restricts the lexical space of the schema type, not its value space. Expressing a three-digit number as a restriction of integer with the pattern facet “[0-9]{3}” creates a schema type whose legal values are only those with a lexical form consisting of three digits.

The pattern facet is not reversible in practice; given an arbitrary pattern, there’s no practical way to determine how the lexical form of a typed value must be constructed so that the result will satisfy that pattern.

As a consequence, pattern facets are not respected during serialization and values in the data model that were originally valid with respect to a schema that contains pattern-based restrictions may not be valid after serialization.

 Undefined Values

Some typed values in the data model are undefined. Attempting to access an undefined property always raises an error.

 Data Model Serialization

Serialization of an instance of the data model is governed by .

 Infoset Mapping

This specification describes how to map each kind of node to the corresponding information item. This mapping produces an Infoset, it does not and cannot produce a PSVI. Validation must be used to obtain a PSVI for a (portion of a) data model instance.

Accessors

A set of accessors is defined on all seven kinds of nodes, see . Some accessors return a constant empty sequence on certain node kinds. The unparsed-entity-system-id, unparsed-entity-public-id, and document-uri accessors, which are only available on &documentNode;s, and the in-scope-namespaces accessor, which is only available on &elementNode;s are not included in this summary.

In order for processors to be able to operate on instances of the data model, the model must expose the properties of the items it contains. The data model does this by defining a family of accessor functions. These are not functions in the literal sense, they are not available for users or applications to call directly, rather they are descriptions of the information that an implementation of the data model must expose to applications. Functions and operators available to end-users are described in .

base-uri Accessor

The base-uri accessor returns the base URI of a node as a sequence containing zero or one URI reference. For more information about base URIs, see .

It is defined on all seven node kinds.

 node-name Accessor

The node-name accessor returns the name of the node as a sequence of zero or one xs:QNames.

It is defined on all seven node kinds.

 parent Accessor

The parent accessor returns the parent of a node as a sequence containing zero or one nodes.

It is defined on all seven node kinds.

 string-value Accessor

The string-value accessor returns the string value of a node.

It is defined on all seven node kinds.

 typed-value Accessor

The typed-value accessor returns the typed-value of the node as a sequence of zero or more atomic values.

It is defined on all seven node kinds.

 type-name Accessor

The type-name accessor returns the name of the schema type of a node as a sequence of zero or one xs:QNames.

It is defined on all seven node kinds.

 children Accessor

The children accessor returns the children of a node as a sequence containing zero or more nodes.

It is defined on all seven node kinds.

 attributes Accessor

The attributes accessor returns the attributes of a node as a sequence containing zero or more &attributeNode;s. The order of &attributeNode;s is stable but implementation dependent.

It is defined on all seven node kinds.

 namespaces Accessor

The namespaces accessor returns the namespaces associated with a node as a sequence containing zero or more &namespaceNode;s. The order of &namespaceNode;s is stable but implementation dependent.

It is defined on all seven node kinds.

 nilled Accessor

The nilled accessor returns true if the node is nilled, see .

It is defined on all seven node kinds.

 Nodes

The seven distinct kinds of Node: document, element, attribute, text, namespace, processing instruction, and comment, are defined in the following subsections.

All nodes must satisfy the following general constraints:

Every node must have a unique identity, distinct from all other nodes.

The &dm.prop.children; property of a node must not contain two consecutive &textNode;s.

The &dm.prop.children; property of a node must not contain any empty &textNode;s.

The sequence of nodes in the &dm.prop.children; property of a node is ordered and must be in document order.

The &dm.prop.children; and &dm.prop.attributes; properties of a node must not contain two nodes with the same identity.

 &Document; ∈ &Attribute; &Namespace; &ProcessingInstruction; &Comment; &Text; Conformance

The data model is intended primarily as a component that can be used by other specifications. Therefore, the data model relies on specifications that use it (such as , , and ) to specify conformance criteria for the data model in their respective environments. Specifications that set conformance criteria for their use of the data model must not relax the constraints expressed in this specification.

Authors of conformance criteria for the use of the data model should pay particular attention to the following features of the data model:

Support for DTD processing (both validation and unparsed entities).

Support for W3C XML Schema processing.

Support for the normative construction from an infoset described in .

Support for the normative construction from a PSVI described in .

Support for XML 1.0 and XML 1.1.

XML Information Set Conformance

This specification conforms to the XML Information Set . The following information items must be exposed by the infoset producer to construct a data model unless they are explicitly identified as optional:

The Document Information Item with base URI and children properties.

Element Information Items with base URI, children, attributes, in-scope namespaces, local name, namespace name, parent properties.

Attribute Information Items with namespace name, local name, normalized value, attribute type, and owner element properties.

Character Information Items with character code and parent properties.

Processing Instruction Information Items with base URI, target, content and parent properties.

Comment Information Items with content and parent properties.

Namespace Information Items with prefix (optional) and namespace name properties.

Other information items and properties made available by the Infoset processor are ignored. In addition to the properties above, the following properties are required from the PSVI if the data model is constructed from a PSVI:

validity, type definition, type definition namespace, type definition name, type definition anonymous, member type definition, member type definition namespace, member type definition name, member type definition anonymous and schema normalized value properties on Element Information Items.

validity, type definition, type definition namespace, type definition name, type definition anonymous, member type definition, member type definition namespace, member type definition name, member type definition anonymous and schema normalized value properties on Attribute Information Items.

 Error Summary

This error is raised whenever an accessor is called for a property that is undefined.

 References Normative References Other References XML Query Data Model, Mary Fernández and Jonathan Robie, Editors. World Wide Web Consortium, 15 Feb 2001. XML Query Working Group, World Wide Web Consortium. Home page: http://www.w3.org/XML/Query XSL Working Group, World Wide Web Consortium. Home page: http://www.w3.org/Style/XSL/ ISO (International Organization for Standardization). Representations of dates and times, 2000-08-03. Available from: http://www.iso.ch/ Glossary Example This appendix does not exactly reflect the current state of the documents. It will be updated before the next publication.

The following XML document is used to illustrate the information contained in a data model:

&dm-example.xml;

The document is associated with the URI http://www.example.com/catalog.xml, and is valid with respect to the following XML schema:

&dm-example.xsd;

This example exposes the data model for a document that has an associated schema and has been validated successfully against it. In general, an XML Schema is not required, that is, the data model can represent a schemaless, well-formed XML document with the rules described in .

The XML document is represented by the nodes described below. The value D1 represents a &documentNode;; the values E1, E2, etc. represent &elementNode;s; the values A1, A2, etc. represent &attributeNode;s; the values N1, N2, etc. represent &namespaceNode;s; the values P1, P2, etc. represent &processingInstructionNode;s; the values T1, T2, etc. represent &textNode;s.

For brevity:

&textNode;s in the data model that contain only white space are not shown.

Literal strings are shown in quotes without the xs:string() constructor

Literal decimals are shown without the xs:decimal() constructor

Nodes are referred to using the syntax [nodeID]

xs:QNames are used with the following prefixes:

xshttp://www.w3.org/2001/XMLSchema
xsihttp://www.w3.org/2001/XMLSchema-instance
cathttp://www.example.com/catalog
xlinkhttp://www.w3.org/1999/xlink
htmlhttp://www.w3.org/1999/xhtml

The abbreviation \n is used in string literals to represent a newline character; this isn't supported in XPath, but it makes this presentation clearer.

Accessors that return the empty sequence have been omitted.

To simplify the presentation, we’re assuming an implementation that does not expose the namespace axis. Therefore, &namespaceNode;s are shared across multiple elements. See .

 &dm-example.tbl;

A graphical representation of the data model for the preceding example is shown below. Document order in this representation can be found by following the traditional in-order, left-to-right, depth-first traversal; however, because the image has been rotated for easier presentation, this appears to be in-order, bottom-to-top, depth-first order.

Graphic representation of the data model. [large view, SVG]