permits xs:dateTime, xs:date, and xs:time values both with and without timezones. In the context of validation, this is a purely lexical distinction. In order to compare dates and times, an XML Schema validator converts all times to Coordinated Universal Time (UTC or timezone Z). But 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 are represented as tuples in the data model: a time value normalized to UTC and a timezone represented as a xdt:dayTimeDuration.

The lexical representation of the value is converted to UTC as defined by and the timezone in the lexical representation is converted to a xdt:dayTimeDuration value. These two values are stored in the tuple.

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

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

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.

If the validity property exists on an element node and is "valid" then &dm.prop.nilled; may be set. The &dm.prop.nilled; property is never set for nodes that have not been successfully schema validated.

If the element is valid and has a PSVI nil property and that property is true, then &dm.prop.nilled; is true. In all other cases, &dm.prop.nilled; is false.

The base-uri accessor returns a sequence containing zero or one uri references.

Document, element, and processing-instruction nodes have a base-uri property. The base-uri of all other node types is the empty sequence.

If the base-uri property of a document, element, or processing-instruction node is non-empty, its value is returned.

If the accessor is called on a node that does not have a base-uri property, or whose base-uri property is empty, the base-uri of that node's parent is returned. If the node has no parent, the empty sequence is returned.

The node-kind accessor returns a string value identifying the kind of node on which the accessor was called. One of the following values is returned:

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

The parent accessor returns a sequence containing zero or one nodes.

For nodes that have a parent, parent returns the parent node. For all other nodes, it returns the empty sequence.

If the return value is not the empty sequence, it will always be either an element node or a document node.

Every node has a string value; the way in which the string value of a node is computed is different for each kind of node and is specified in the sections on nodes below.

The string value of an atomic value is computed by casting it to an xs:string as per the rules described in .

The typed-value accessor returns the typed-value of the node, which is a sequence of zero or more atomic values derived from the string-value of the node and its type in such a way as to be consistent with validation.

For detailed semantics see .

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

The type accessor returns the name of the type of a node.

For element nodes and attribute nodes, type returns the name of the type of the node (as an xs:QName) if it has one. If the type is anonymous, or if no type information exists, the name returned will be unique but implementation defined.

For text nodes, type returns xdt:untypedAtomic.

For other node kinds, it always returns the empty sequence.

The children accessor returns a sequence containing zero or more nodes.

For document and element nodes, it returns the nodes that are the children of that node in document order. It returns the empty sequence for document and element nodes that have no children. If children exist, they will always consist exclusively of element, processing-instruction, comment, and text nodes. Attribute, namespace, and document nodes can never appear as children.

For all other nodes, it always returns the empty sequence.

A document node or an element node is the parent of each of its child nodes. Nodes never share children: if two nodes have distinct identities, then no child of one node will be a child of the other node.

The sequence of children will never contain adjacent text nodes.

The attributes accessor returns a sequence containing zero or more attribute nodes.

For element nodes, these are the attributes of the node. For all other nodes, it always returns the empty sequence.

The namespaces accessor returns a sequence containing zero or more namespace nodes.

For element nodes, these are the namespaces of the node. For all other nodes, it always returns the empty sequence.

The nilled accessor returns the setting of the &dm.prop.nilled; property of an element node. See .

For all other nodes, it always returns the emtpy sequence.

Document nodes encapsulate XML documents. Documents have the following properties:

Document nodes must satisfy the following constraints.

In a well-formed document, the children of the document node must not be empty and consist exclusively of element nodes, processing-instruction nodes, and comment nodes, and exactly one of these children is an element node. A document node in the data model is more permissive: it may be empty and it allows more than one element node as a child and also permits text nodes as children.

Implementations that support DTD processing and access to the unparsed entity accessors, use the unparsed-entities property to associate information about an unordered collection of unparsed entities with a document node.

Three additional accessors are defined on document nodes:

The unparsed-entity-system-id accessor returns the system identifier of an unparsed external entity declared in the specified document. If no entity with the name specified in $entityname exists, or if the entity is not an external unparsed entity, the empty sequence is returned.

The unparsed-entity-public-id accessor returns the public identifier of an unparsed external entity declared in the specified document. If no entity with the name specified in $entityname exists, or if the entity is not an external unparsed entity, or if the entity has no public identifier, the empty sequence is returned.

The document-uri accessor returns the absolute URI of the resource from which the document node was constructed, if the absolute URI is available. If there is no URI available, or if it cannot be made absolute when the data model is constructed, the empty sequence is returned.

For example, if a collection of documents is returned by the fn:collection function, the document-uri may serve to distinguish between them even though each has the same base-uri.

When a data model fragment is created from the PSVI, a document information item is mapped to a Document Node. The precise transformation is described by specifying the PSVI property corresponding to each property of a document node.

To construct the value of the &dm.prop.children; property, for each element, processing instruction, comment, and maximal sequence of adjacent character information items found in the children property, a corresponding Element, Processing Instruction, Comment, and Text node is constructed and that sequence of nodes is used as the value. If present among the children, the document type declaration information item is ignored.

The mapping of the data model to the XML Information Set maps a Document Node to a document information item. The properties of the document information item are constructed as follows:

Element nodes encapsulate XML elements. Elements have the following properties:

Element nodes must satisfy the following constraints.

The data model does not enforce a constraint that the namespaces of an element must be a superset of the namespaces of its parent, nor does it enforce a constraint that the namespaces of an element must include namespace nodes for each of the namespace URIs used in the element name and the names of its attributes, or of namespace URIs used in the content of elements and attributes of type xs:QName. Applications of the data model (such as XSLT and XQuery) may enforce such constraints in particular circumstances, but these constraints are not part of the data model.

The base-uri accessor returns the &dm.prop.base-uri; property of the element node, if it exists. If it does not exist, the base URI of the element's parent is returned.

The accessors namespaces and attributes return the same set of namespace and attribute nodes (respectively) associated with the element. They are not constrained to return them in any particular order.

The parent accessor returns the empty sequence if the element has no parent.

If the element node's type is xs:anyType, the typed-value accessor returns the node's string value as xs:anySimpleType. If the type is a complex type with complex content, invoking typed-value raises an error.

The typed-value accessor returns the typed-value of the node, which is a sequence of zero or more atomic values. The typed-value is closely related to the node's string-value and its type. For example:

In fact, when the type is an atomic type, typed-value is always the atomic-value constructed from the string-value and the type.

In the general case, typed-value constructs a sequence of atomic values. These values are derived from the string-value of the element and its type, in such a way as to be consistent with validation.

One additional accessors is defined on element nodes:

The element-declaration accessor returns the xs:QName of the global element declaration associated with this element. If the element declaration is local, it returns a sequence consisting of the xs:QName of the local element declaration and the SchemaGlobalContext of the declaration.

This declaration can be used by implementations to identify substitution groups, nillability, and other aspects of the declaration.

When a data model fragment is created from the PSVI, an element information item is mapped to an Element Node. The precise transformation is described by specifying the PSVI property corresponding to each property of an element node.

The mapping of the data model to the XML Information Set maps an Element Node to an element information item. The properties of the element information item are constructed as follows:

An implementation must construct the value of the prefix property as if the following algorithm was applied: if the element has at least one namespace node whose namespace URI is the same as the namespace name of the xs:QName returned by the node-name accessor, it returns the local part of the name of that namespace node or the empty string if the namespace node has no name. If there are several such namespace nodes, it chooses one of them arbitrarily. If there is no such namespace node, it generates an arbitrary prefix that is distinct from the node-name of any of the element's namespaces. The prefix is the empty string if the element has an empty namespace name (if it is in the null namespace).

If a new prefix is generated, a corresponding namespace information item must be added to the in-scope namespaces property of the element information item. The namespace information item must associate the generated prefix with the namespace name of the xs:QName returned by the element's node-name accessor.

The namespace attributes property is computed so that it contains the smallest possible set of namespace attributes. For example, suppose that the namespaces accessor for this element returns namespace nodes for the foo, bar, and baz namespaces and the namespaces accessor for this element's parent returns namespace nodes for the foo and bar namespaces. In this case, the namespace attributes property will contain a single namespace information item for the baz namespace.

Attribute nodes encapsulate XML attributes. Attributes have the following properties:

Attribute nodes must satisfy the following constraints.

For convenience, the element node that owns this attribute is called its "parent" even though an attribute node is not a "child" of its parent element.

If the attribute node's type is xs:anySimpleType, the typed-value accessor returns the node's string value as xdt:untypedAtomic.

The typed-value accessor returns the typed-value of the node, which is a sequence of zero or more atomic values. The typed-value is closely related to the node's string-value and its type. For example:

In fact, when the type is an atomic type, typed-value is always the atomic-value constructed from the string-value and the type.

In the general case, typed-value constructs a sequence of atomic values. These values are derived from the string-value of the element and its type, in such a way as to be consistent with validation.

When a data model fragment is created from the PSVI an attribute information item is mapped to an Attribute Node. The precise transformation is described by specifying the PSVI property corresponding to each property of an attribute node.

The mapping of the data model to the XML Information Set maps an Attribute Node to an attribute information item. The properties of the corresponding attribute information item are constructed as follows:

An implementation must construct the value of the prefix property in the following way: if the attribute has a parent, in the same way that a prefix would be constructed for that element, otherwise a non-empty prefix is chosen arbitrarily, and no attempt is made to associate the prefix with the namespace URI.

Namespace nodes encapsulate XML namespaces. Namespaces have the following properties:

Namespace nodes must satisfy the following constraints.

In XPath 1.0, namespace nodes were directly accessible by applications, by means of the namespace axis. In XPath 2.0 the namespace axis is deprecated, and it is not available at all in XQuery 1.0. XPath 2.0 implementations are not required to expose the namespace axis, though they may do so if they wish to offer backwards compatibility. The information held in namespace nodes is instead made available to applications using two functions defined in , namely fn:get-in-scope-namespaces and fn:get-namespace-uri-for-prefix. Certain properties of namespace nodes are not exposed by these functions: in particular, properties related to the identity of namespace nodes, their parentage, and their position in document order. Implementations that do not expose the namespace axis can therefore avoid the overhead of maintaining this information.

When a data model fragment is created from the PSVI a namespace information item is mapped to a Namespace Node. The precise transformation is described by specifying the PSVI property corresponding to each property of a namespace node.

The mapping of the data model to the XML Information Set maps a Namespace Node to a namespace information item. The properties of the namespace information item are constructed as follows:

Processing instruction nodes encapsulate XML processing instructions. Processing instructions have the following properties:

Namespace nodes must satisfy the following constraints.

When a data model fragment is created from the PSVI, a processing instruction information item is mapped to a Processing Instruction Node. The precise transformation is described by specifying the PSVI property corresponding to each property of a processing instruction node.

There are no processing instruction nodes for processing instructions that are children of a document type declaration information item.

The mapping of the data model to the XML Information Set maps a Processing Instruction Node to a processing instruction information item. The properties of the processing instruction information item are constructed as follows:

Comment nodes encapsulate XML comments. Comments have the following properties:

Comment nodes must satisfy the following constraints.

When a data model fragment is created from the PSVI a comment information item is mapped to a Comment Node. The precise transformation is described by specifying the PSVI property corresponding to each property of a comment node.

There are no comment nodes for comments that are children of a document type declaration information item.

The mapping of the data model to the XML Information Set maps a Comment Node to a comment information item. The properties of the corresponding comment information item are constructed as follows:

Text nodes encapsulate XML character content. Text has the following properties:

Text nodes must satisfy the following constraint:

In addition, document and element nodes impose the constraint that two consecutive text nodes can never occur as adjacent siblings.

When a data model fragment is created from the PSVI a maximal sequence of consecutive character information items are mapped to a Text Node. The precise transformation is described by specifying the PSVI property corresponding to each property of a text node.

The mapping of the data model to the XML Information Set maps a Text Node to a sequence of character information items. The properties of the corresponding character information items are constructed as follows: