Navigating XML

Overview

Xpath is a non-xml syntax to be used with XSLT and Xpointer. Its purpose according to the W3.org is to address parts of an XML document. In support of

this primary purpose, it also provides basic facilities for manipulation of strings, numbers and booleans. XPath uses a compact, non-XML syntax to facilitate use of XPath within URIs and XML attribute values. XPath operates on the abstract, logical structure of an XML document, rather than its surface syntax. XPath gets its name from its use of a path notation as in URLs for navigating through the hierarchical structure of an XML document.

The Xpath Expression

An Xpath expression consists of a location path and one or more location steps.

Each location step consists of an axis, a node test and a predicateaxis::nodetest[predicate]

One or more of these elements may be absent but if both axis and nodetest are present they must be separated by :: and if the predicate is present it must be in [ ]

First a Few Terms

Node Node-set Context Node Location Path

Node

There are seven types of nodes The document as a whole Element nodes (one for each element in

a document) Attribute nodes Comment nodes Processing instructions Namespace nodes Text nodes

Node-set

A node-set is a group of nodes returned by a single xpath expression

(This has important implications for Xpointers where sets of information could be returned from a remote document and embedded in a new or current document)

Context-node

The context node identifies where in the document to start applying a given set of instructions

Location Path

The location path is simply the path or instructions for getting to a particular point in a document

Axis

The axis determines which direction you want to move in the document

Directions are like “next node”, preceding node”, “Parent node”, “Child node”

Some Axis Directions

childchild One step down the element treeOne step down the element tree

parentparent One step up the element treeOne step up the element tree

attributeattribute Looks at the attributes of the context nodeLooks at the attributes of the context node

ancestorancestor Looks up the tree but doesn’t include Looks up the tree but doesn’t include context node itselfcontext node itself

descendentdescendent Reverse of ancestorReverse of ancestor

followingfollowing All the nodes after the context nodesAll the nodes after the context nodes

precedingpreceding All the nodes before the context nodesAll the nodes before the context nodes

namespacenamespace Gets all the namespace nodes for the Gets all the namespace nodes for the current elementcurrent element

selfself Just the context node itselfJust the context node itself

Axis Short Cut Syntax

child::orderchild::order orderorder Child is the defaultChild is the default

order/*order/*

order/@order/@

Selects any child of orderSelects any child of order

Selects any attribute of Selects any attribute of orderorder

order::attribute::order::attribute::

quantityquantity

order/order/@quantity@quantity

Selects attribute quantity Selects attribute quantity from order elementfrom order element

descendant-or-descendant-or-self::orderself::order

//order//order Any descendent of order or Any descendent of order or the order element itselfthe order element itself

Nodetest

There are three kinds of node test Name test—tests the names along the

specified path Node types—tests for the type of node along

the specified path (comment, node, processing-instruction or text)

Literal text—locates the literal text

preceding::processing-instruction(“xml:stylesheet”)

Predicate

The predicate part is optional, but can give you more precise control

//customer[@name='John']/@name This has a predicate of

[@name=‘John’] which selects the order that has the name attribute value John

Xpath Function

Xpath also contains many built in functions. Some are:

position()position() ceiling ()ceiling ()

last()last() floor ()floor ()

sum ()sum () round ()round ()

count ()count () substring ()substring ()

An Example: The XML File

<?xml version=“1.0”?><orders> <customer name=“John” > <order quantity=“5”> dinner specials </order> <order quantity=“2”> red wine </order> </customer></orders>

*click here to see the whole file

Selecting one Customer

<h3><xsl:value-of select="//customer[@name='John']/@name"/></h3>

<p><xsl:for-each select="//customer[@name='John']/order">

<xsl:value-of select="@quantity" /><xsl:value-of select="." /></xsl:for-each> </p>

Totaling the orders

<xsl:value-of select="sum(//order/@quantity)" />

Returning the Node Names

<xsl:for-each select="//customer">

<xsl:value-of select="name()"/>

</xsl:for-each>

Count of Nodes

<xsl:value-of select="count(customer)" />