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Introduction of XPath

XPath is the solution to finding information in an XML document. XPath uses expressions to find elements, attributes, and other information in your XML.

XML documents have a tree structure

  1. XPath allows you to concisely describe sets of XML elements and attributes in this tree.
  2. Analogy to file system paths.
  3. A file system hierarchy is a tree of directories and files.
  4. A filesystem path describes how to reach a specific file, starting either from the root, or the current working directory.
  5. XPath exploits this intuitive notion of a path, and extends it to XML documents.
Nodes of XPath

In the XML tree available for XPath expressions, there are 7 node types

  1. The root node (one per document)
  2. Element nodes
  3. Attribute nodes
  4. Text nodes
  5. Comment nodes
  6. Processing instruction nodes
  7. Namespace nodes
Simple Example

<?xml version="1.0" encoding="ISO-8859-1"?>


  <title lang="eng">Harry Potter</title>

  <title lang="eng">Learning XML</title>


Some Expression How to Locate path
Expression Description
/Selects from the root node
//Selects nodes in the document from the current node that match the selection no matter where they are
.Selects the current node
..Selects the parent of the current node
@Selects attributes
Path Expression Result
/bookstoreSelects the root element bookstore
bookstore/bookSelects all book elements that are children of bookstore
//bookSelects all book elements no matter where they are in the document
bookstore//bookSelects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
//@langSelects all attributes that are named lang
Advantage of XPath
  1. Flexible expression- The user may use whatever tags/attributes seem intuitive when designing the schema
  2. latent semantics- Many users prefer to figure out the semantics when/if necessary
  3. Application Specific Constraint Checking
  4. Core Technology- XSLT/XPath is a "core technology" which is well supported, well understood, and with lots of material written on it.
  5. Expressive Power- XSLT/XPath is a very powerful language. Most, if not every, constraint that you might ever need to express can be expressed using 6.XSLT/XPath. Thus you don't have to learn multiple schema languages to express your additional constraints
  6. Long Term Support- XSLT/XPath is well supported, and will be around for a long time.
Disadvantage of XPath
  1. Separate Documents- With this approach you will write your XML Schema document, then you will write a separate XSLT/XPath document to express additional constraints. Keeping the two documents in synch needs to be carefully managed
  2. Efficiency is access limited
XPATH Tutorials
XPATH Examples
XPATH Interview Materials