W3CXML

XPath

Jaroslav Porubän2008

W3CXML XPath Overview

XPath is a language for addressing parts of an XML document

XPath gets its name from its use of a path notation as in URLs

XPath operates on the abstract structure of an XML document

XPath models an XML document as a tree of nodes

XPath does not exist in isolation

W3CXML XPath Overview

XPath in the context of XML technologies is a major element in the XSLT

standard XQuery and XPointer are both built on

XPath expressions XQuery 1.0 and XPath 2.0 share the

same data model and support the same functions and operators

XPath is not an XML language

W3CXML XPath Example

XML<people> <person> <name license="kill"> <first>James</first> <last>Bond</last> </name> <name> <first>Major</first> <last>Zeman</last> </name> </person></people>

XPath/people/person/name/people/person/name/@license/people/person/name[@license="kill"]

W3CXML XPath Nodes

Seven kind of tree nodes: root node element nodes attribute nodes text nodes namespace nodes processing-instruction nodes comment nodes

W3CXML Relationship of Nodes

Parent each element and attribute has one parent

Children element nodes may have one or more

children Siblings

nodes with the same parent Ancestors

node’s parent, parent of parent, ... Descendants

node’s children, children's children, ...

W3CXML Context Node

The context indicates the location of the node where a processor is currently situated – context node

Context includes a context position and a context size

Absolute location path starts with slash /

Relative location path is specified with context in mind

W3CXML XPath Expression

XPath expression consists of a sequence of location steps (separated by /)

Location step is made of Axis A node test An optional predicate

child::person[position()=2]Axis Node test Predicate

W3CXML XPath Axes (Directions)

child axis attribute axis ancestor axis ancestor-or-self axis descendant axis descendant-or-self axis following axis following-sibling axis preceding axis preceding-sibling axis parent axis self axis namespace axis (deprecated in XPath 2.0)

W3CXML child Axis (Default Axis)

Selects nodes that are immediate child nodes of the context node

Selects nodes with name personchild::personperson (abbreviated)

Select all element node (only element nodes have names)child::** (abbreviated)

W3CXML child Axis

Selects all nodes, including comment nodes, processing instruction nodes, and text nodeschild::node()node() (abbreviated)

Selects text nodes onlychild::text()text() (abbreviated)

Selects comment nodes onlychild::comment()comment() (abbreviated)

Selects processing instruction nodes onlychild::processing-instruction()processing-instruction() (abbreviated)

W3CXML attribute Axis

Selects the attribute nodes associated with an element node

Selects attributes with name licenseattribute::license@license (abbreviated)

Select all attribute nodes of the context nodeattribute::*@* (abbreviated)

W3CXML ancestor Axis

Selects the parent node of the context node and its parent up to the hierarchy till the root node of the document is selected

Selects all ancestor nodes of the context node with name personancestor::person

Selects all ancestor nodes of the context nodeancestor::*

W3CXML ancestor-or-self Axis

Selects the context node and its parent node and its parent up to the hierarchy till the root node of the document is selected

Selects context node and all ancestor nodes of the context node with name personancestor-or-self::person

Selects context node and all ancestor nodes of the context nodeancestor-or-self::*

W3CXML descendant Axis

Selects the child nodes of the context node, the child nodes of those child nodes down to the hierarchy

Selects the context node and all descendant nodes of the context node with name firstdescendant::first

Selects the context node and all descendant nodes of the context nodedescendant::*

W3CXML descendant-or-self Axis

Selects the context node and child nodes of the context node, the child nodes of those child nodes down to the hierarchy

Selects the context node and all descendant nodes of the context node with name firstdescendant-or-self::first//first (abbreviated)

Selects the context node and all descendant nodes of the context nodedescendant-or-self::*

W3CXML following Axis

Selects all nodes that come after the context node in document order, but excludes all descendant nodes and any attribute nodes and namespace nodes associated with the context node

Selects the following nodes of the context node with name firstfollowing::first

Selects following nodes of the context nodefollowing::*

W3CXML following-sibling Axis

Selects all sibling nodes that share their parent node with the context node

Selects the following sibling nodes of the context node with name firstfollowing-sibling::first

Selects following sibling nodes of the context node

following-sibling::*

W3CXML preceding Axis

Selects all nodes that come before the context node in document order, excluding nodes in the ancestor axis and attribute and namespace nodes

Selects the preceding nodes of the context node with name firstpreceding::first

Selects preceding nodes of the context nodepreceding::*

W3CXML preceding-sibling Axis

Selects those nodes that are in the preceding axis and that also share a parent node with the context node

Selects the preceding sibling nodes of the context node with name firstpreceding-sibling::first

Selects preceding sibling nodes of the context nodepreceding-sibling::*

W3CXML parent Axis

Selects the parent node of the context node

Selects the parent node with name person if existsparent::person

Selects the parent nodeparent::node().. (abbreviated)

W3CXML self Axis

Selects the context node

Selects the context nodeself::node(). (abbreviated)

W3CXML namespace Axis

Selects namespace nodes. An element node has a separate namespace node for each in-scope namespace.

Selects the namespace nodes of the context node with name firstxmml::first

W3CXML XPath Datatypes

An expression is evaluated to: node-set (an unordered collection of

nodes without duplicates) boolean (true or false) number (a floating-point number) string (a sequence of unicode

characters)

W3CXML XPath Operators

W3CXML XPath Functions

XPath 1.0 Functions Boolean Functions Node-Set Functions Numeric Functions String Functions

W3CXML Boolean XPath Functions

boolean(object)- takes an object as its argument and returns a boolean value

false()- returns the boolean value false true()- returns the boolean value true not(boolean)- returns true if the argument

evaluates to false, and false if the argument evaluates to true

lang(string) - returns true if the language of the context node is the language indicated by the string argument or one of its sublanguages

W3CXML Node-Set XPath Functions

count(node-set)- returns a number of nodes in the node-set

position()- returns a value equal to the context position

last()- returns a value equal to the context size id(object)- returns a node-set containing any

node that has an attribute of type ID equal to the function’s argument

local-name(node-set?)- returns the local part of the element name if it exists

name(node-set?)- returns the name of the node in prefix:localpart format

namespace-uri(node-set?) - returns the namespace URI

W3CXML Numeric XPath Functions

number(object?)- takes a string, boolean or node-set as its argument and returns a number

ceiling(number)- returns the smallest integer greater than this

floor(number)- returns the largest integer that is lower than this

round(number)- returns the integer that is closest to the number argument

sum(node-set)- returns the sum of the value of each individual node after converting the values to a numeric type if possible. Be careful when using sum()

W3CXML String XPath Functions

string(object?)- takes a boolean, node-set, or number as its argument and returns a string value

concat(string, string, string*)- returns the concatenation of its arguments

starts-with(string, string)- returns true if the first argument string starts with the second argument string, and otherwise returns false

contains(string, string)- returns true if the first argument string contains the second argument string, and otherwise returns false

substring(string, number, number?)- returns the substring of the first argument starting at the position specified in the second argument with length specified in the third argument.

W3CXML String XPath Functions

substring-after(string, string)- returns the substring of the first argument string that follows the first occurrence of the second argument string in the first argument string, or the empty string if the first argument string does not contain the second argument string.

substring-before(string, string)- function returns the substring of the first argument string that precedes the first occurrence of the second argument string in the first argument string, or the empty string if the first argument string does not contain the second argument string

string-length()- number of characters in the string

W3CXML String XPath Functions

normalize-space(string?)- returns the argument string with whitespace normalized by stripping leading and trailing whitespace and replacing sequences of whitespace characters by a single space

translate(string, string, string)- returns the first argument string with occurrences of characters in the second argument string replaced by the character at the corresponding position in the third argument string

W3CXML XPath Predicates

Predicates are used to filter node-sets selected using an axis and location step

A predicate is optional in each location step of an XPath expression

There can be more than one predicate in any one location step.

/people/person[@licence="kill"]//person[@licence="kill"][@weapon="wisdom"]

W3CXML XPath User Functions

Set of predefined functions can be extended by user defined functions if needed

User XPath functions are implemented in the context of XPath processor