Glossary

This glossary gathers together some of the more common technical terms used in this book. Most of these terms are defined in the XSLT or XPath specifications, but some of them are borrowed from XML or other standards in the XML family, and one or two have been invented for the purposes of this book. So for each definition, I also tell you where the term comes from.

The definitions in all cases are my own; in some cases the original specifications have a much more formal definition, but in other cases they are surprisingly vague.

Where a definition contains references to other terms defined in the glossary, these terms are written in italic.

A-C

ANCESTOR AXIS (XPATH)

The ancestor axis selects the parent of the context node, its parent, and so on, up to and including the root node. This axis is a reverse axis.

ANCESTOR-OR-SELF AXIS (XPATH)

The ancestor-or-self axis selects the context node followed by all the nodes on the ancestor axis. This axis is a reverse axis.

ARITY (XPATH)

The arity of a function is the number of parameters defined in the function signature: for example the arity of the function true() is zero, while the two versions of the contains() function have arity two and three respectively.

ATOMIC VALUE (XPATH)

An atomic value is an item such as an integer, a string, a date, or a boolean. Specifically, it is an instance of the class xdt:anyAtomicType , which includes all simple types (as defined in XML Schema) that are not list types or union types.

ATOMIZATION (XPATH)

Atomization is a process that takes an arbitrary sequence, containing a mixture of nodes and atomic values, and creates a new sequence in which each of the nodes is replaced by its typed value. Atomic values appearing in the input sequence are retained in the result sequence unchanged.

ATTRIBUTE ( XML )

A name =value pair appearing in an element 's start tag, for example «category="grocery" » .

ATTRIBUTE AXIS (XPATH)

The attribute axis selects all the attributes of the context node. If the context node is not an element, the axis will be empty.

ATTRIBUTE DECLARATION (SCHEMA)

An attribute declaration is a schema component corresponding to an <xs:attribute> element in a schema: it defines constraints on the values of attributes having a particular name. It may be a global attribute declaration (if it is defined at the top level of a schema) or a local attribute declaration (if defined within the structure of a complex type ).

ATTRIBUTE NODE (XPATH)

A node in a tree that represents an attribute in an XML document. There will be an attribute node attached to an element node for each attribute defined in the start tag of the corresponding element in the original XML document, other than an attribute acting as a namespace declaration. There will also be attribute nodes for attributes given a default value in the document type definition. The string value of the node is the value of the attribute; its typed value is the result of validating the string value against the relevant type definition in a schema.

ATTRIBUTE SET ( XSLT )

A named collection of <xsl:attribute> instructions, which when invoked using the use-attribute-sets attribute of <xsl:element> or <xsl:copy> , or the xsl:use-attribute-sets attribute of a literal result element, generates a set of attribute nodes to be added to the result sequence.

ATTRIBUTE VALUE TEMPLATE ( XSLT )

An attribute value template is an attribute in the stylesheet that can contain both fixed and variable parts. The fixed parts are written as ordinary characters , while the variable parts are written between curly braces: for example, «file="{$dir}/{$fname}.html" » would evaluate to «file="out/page.html" » if the variables $dir and $fname have the values «out » and «page » respectively. Attribute value templates can be used for any attribute of a literal result element, but on XSLT elements they can be used only for those attributes that explicitly allow them.

AXIS ( XPATH )

An axis is a direction of travel through the tree. Starting from a particular context node, an axis defines a list of nodes reached from that origin. For example, the ancestor axis returns the parent, grandparent, and so on up to the root of the tree, while the following sibling axis returns all the nodes that appear after the context node and share the same parent.

BASE URI ( XPATH )

Every node has an associated base URI. For an element, this is the absolute URI of the XML external entity containing the element's start and end tags (most often, of course, this will be the document entity). For other node types, it is defined by reference to an associated element node, typically its parent. The base URI of an element can also be set explicitly by using the xml:base attribute. The base URI of a node is used when expanding a relative URI defined in that node, for example a relative URI in an href attribute is considered to be relative to the base URI of the parent element.

Every XPath expression also has a base URI defined as part of its static context. For an XPath expression contained in a stylesheet, this is the base URI of the stylesheet element containing the XPath expression. In non-XSLT contexts, it's up to the host environment to specify a base URI for the expression.

BOOLEAN (XPATH)

One of the allowed data types for the value of an XPath expression. It takes the value true or false.

BUILT-IN TEMPLATE RULE ( XSLT )

A template rule that is not explicitly defined in the stylesheet, but that is implicitly available to process a node if there is no explicit template rule that matches it.

BUILT-IN TYPE (SCHEMA)

The XML Schema specification defines a number of built-in simple types that are available for use, without any need to declare them in a schema. These include 19 primitive types (such as xs:string and xs:date ), 20 built-in derived atomic types (including xs:integer and xs:ID ), and 3 built-in list types ( xs:NMTOKENS , xs:IDREFS , and xs:ENTITIES ).

CAST ( XPATH )

An expression that converts an atomic value of one type to an atomic value of a different type.

CDATA SECTION ( XML )

A sequence of characters in an XML document enclosed between the delimiters «![CDATA[ » and «] ]> » ; within a CDATA section all characters represent text content rather than markup, except for the sequence «] ]> » .

CHARACTER REFERENCE ( XML )

A representation of a character using its decimal or hexadecimal Unicode value, for example «&#10; » or «&#x21A4; » . Normally used for characters that are difficult or impossible to enter directly at the keyboard. Character references appear in lexical XML documents, but in the XPath data model they are replaced by the characters that they represent.

CHILD AXIS (XPATH)

The child axis selects all the immediate children of the context node. These can include elements, text nodes, comments, and processing instructions, but not attributes or namespace nodes. This is a forwards axis.

CODEPOINT (UNICODE)

A numeric value identifying a Unicode character.

CODEPOINT COLLATION (XPATH)

A collation that compares and sorts strings strictly according to the numeric values of the codepoints making up the characters of the string.

COLLATION (XPATH)

A set of rules for comparing strings. A collation can be used to decide whether two strings are equal, to decide how they should be ordered, and to decide whether one string is a substring of another. Different collations are needed to satisfy the needs of different languages or different applications. In XPath and XSLT a collation is identified by a URI. Except for the codepoint collation, the URIs used to identify collations are defined by the implementation.

COMMENT (XML)

Markup in an XML document that is conventionally used to carry extraneous information that is not part of the document proper. Written between the delimiters «<!-- » and «--> » .

COMMENT NODE (XPATH)

A node in a tree representing an XML comment. The string value of the node is the text of the comment.

COMPLEX TYPE (SCHEMA)

A schema type that describes the structure of elements that may have child elements or attributes. If the type permits attributes but not child elements, it is referred to as a complex type with simple content.

CONSTRUCTOR FUNCTION (XPATH)

A function that constructs an atomic value of a particular type. The function has the same name as the target atomic type, and always takes a single argument. A constructor function is created automatically for every atomic type, including user -defined atomic types. An example of a call on a constructor function is «xs:date("2004-02-29") » . The semantics of constructor functions are defined by reference to the rules for cast expressions.

CONTEXT ITEM ( XPATH )

The item currently being processed ; part of the dynamic context. Certain XSLT instructions and XPath expressions place a new context item on the stack, and revert to the previous context item when the instruction or expression has been evaluated. The XSLT instructions <xsl:apply-templates> and <xsl:for-each> change the context item, as do the XPath expressions «E1/E2 » and «E1[E2] » . The context item can be retrieved using the expression «. » .

CONTEXT NODE (XPATH)

If the context item is a node, then the context node is the same thing as the context item. If the context item is not a node, then the context node is undefined.

CONTEXT POSITION ( XPATH )

When a sequence of items is processed in an expression of the form «E1/E2 » or «E1[E2] » , or by an <xsl:for-each> or <xsl:apply-templates> instruction in XSLT, each item in the sequence in turn becomes the context item, and the context position identifies the position of the context item in the sequence being processed. The context position determines the value of the position() function, and is also used in evaluating a numeric predicate such as «[1] » .

CONTEXT SIZE (XPATH)

When a sequence of items is processed in an expression of the form «E1/E2 » or «E1 [E2] » , or by an <xsl:for-each> or <xsl:apply-templates> instruction in XSLT, each item in the sequence in turn becomes the context item, and the context size identifies the number of items in the sequence being processed. The context size determines the value of the last() function.

CURRENT MODE ( XSLT )

When a template rule is invoked, the mode used in the <xsl:apply-templates> instruction that invoked it is called the current mode. A further call of <xsl:apply-templates> within this template rule can specify «mode="#current" » to continue processing in the current mode.

CURRENT TEMPLATE RULE ( XSLT )

When <xsl:apply-templates> selects a template rule to process a particular node, that template rule becomes the current template rule. It remains the current template rule through calls of <xsl:call-template> , but not through calls of <xsl:for-each> . The current template rule is used only in deciding which template rule to invoke when <xsl: apply-imports > is called.