XPath

1
XPath

• Navigating XML

2
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.

3
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
• axisnodetestpredicate
• 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

4
First a Few Terms

• Node
• Node-set
• Context Node
• Location Path

5
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

6
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)

7
Context-node

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

8
Location Path

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

9
Axis

• The axis determines which direction you want to
  move in the document
• Directions are like next node, preceding node,
  Parent node, Child node

10
Some Axis Directions
11
Axis Short Cut Syntax
12
Nodetest

• There are three kinds of node test
• Name testtests the names along the specified
  path
• Node typestests for the type of node along the
  specified path (comment, node, processing-instruct
  ion or text)
• Literal textlocates the literal text
• precedingprocessing-instruction(xmlstylesheet
  )

13
Predicate

• The predicate part is optional, but can give you
  more precise control
• //customer_at_name'John'/_at_name
• This has a predicate of _at_nameJohn which
  selects the order that has the name attribute
  value John

14
Xpath Function

• Xpath also contains many built in functions. Some
  are

15
An Example The XML File

• lt?xml version1.0?gtltordersgt ltcustomer
  nameJohn gt ltorder quantity5gt dinner
  specials lt/ordergt ltorder quantity2gt
  red wine lt/ordergt lt/customergtlt/ordersgt
• click here to see the whole file

16
Selecting one Customer

• lth3gtltxslvalue-of select"//customer_at_name'John'
  /_at_name"/gtlt/h3gt
• ltpgt
• ltxslfor-each select"//customer_at_name'John'/ord
  er"gt
• ltxslvalue-of select"_at_quantity" /gt
• ltxslvalue-of select"." /gt
• lt/xslfor-eachgt
• lt/pgt

17
Totaling the orders

• ltxslvalue-of select"sum(//order/_at_quantity)" /gt

18
Returning the Node Names

• ltxslfor-each select"//customer"gt
• ltxslvalue-of select"name()"/gt
• lt/xslfor-eachgt

19
Count of Nodes

• ltxslvalue-of select"count(customer)" /gt