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 predicate axis::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 child One step down the element tree parent One step up the element tree attribute Looks at the attributes of the context node ancestor Looks up the tree but doesn’t include context node itself descendent Reverse of ancestor following All the nodes after the context nodes preceding All the nodes before the context nodes namespace Gets all the namespace nodes for the current element self Just the context node itself

Axis Short Cut Syntax child::orderorder Child is the default Selects any child of order Selects any attribute of order order::attribute::quantity ntity Selects attribute quantity from order element descendant-or- self::order //order Any descendent of order or the 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  This has a predicate of which selects the order that has the name attribute value John

Xpath Function  Xpath also contains many built in functions. Some are: position() ceiling () last() floor () sum () round () count () substring ()

An Example: The XML File dinner specials red wine *click here to see the whole filehere

Selecting one Customer

Totaling the orders

Returning the Node Names

Count of Nodes