XPath (http://www.w3school.com.cn/xpath/xpath_syntax.asp)

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• The most useful path expressions are listed below:
• Instance
• Instance
• Instance
• Instance

XPath uses path expressions to select nodes or node sets in XML documents. Nodes are selected by following the path or step (steps.

XML instance document

We will use this XML document in the following example.

 
<? XML version = "1.0" encoding = "ISO-8859-1"?> <Bookstore> <book> <title lang = "eng"> Harry Potter </title> <price> 29.99 </price> </book> <title lang =" eng "> learning XML </title> <price> 39.95 </price> </book> </bookstore>
 

Select Node

XPath uses path expressions to select nodes in XML documents. Nodes are selected by following the path or step.

The most useful path expressions are listed below:

Expression	Description
Nodename	Select all child nodes of this node
/	Select from Root Node
//	Select the nodes in the document from the current node that matches the selected node, regardless of their location
.	Select current node
..	Select the parent node of the current node
@	Select attributes

Instance

In the following table, we have listed some path expressions and expression results:

Path expression	Result
Bookstore	Select All subnodes of the bookstore Element
/Bookstore	Select the root element bookstore Note: If the path starts with a forward slash (/), the path always represents the absolute path to an element!
Bookstore/book	Select the book elements of all the sub-elements of the bookstore.
// Book	Select All book child elements regardless of their location in the document.
Bookstore // book	Select the book elements of all future generations of the bookstore elements, regardless of their location under the bookstore.
// @ Lang	Select all properties named Lang.

Predicates)

It is used to find a specific node or a node that contains a specified value.

The predicates are embedded in square brackets.

Instance

In the following table, we list some path expressions with predicates and the results of the expressions:

Path expression	Result
/Bookstore/book [1]	Select the first book element that belongs to the bookstore sub-element.
/Bookstore/book [last ()]	Select the last book element that belongs to the bookstore sub-element.
/Bookstore/book [last ()-1]	Select the penultimate book element that belongs to the bookstore sub-element.
/Bookstore/book [position () <3]	Select the first two bookstore sub-elements.
// Title [@ Lang]	Select all the title elements with the lang attribute.
// Title [@ lang = 'eng']	Select All title elements and these elements have the lang attribute whose value is Eng.
/Bookstore/book [price> 35.00]	Select the book element of all the bookstore elements, and the value of the price element must be greater than 35.00.
/Bookstore/book [price> 35.00]/Title	Select the title element of the book element in all the bookstore elements, and the value of the price element must be greater than 35.00.

Select unknown Node

The XPath wildcard can be used to select unknown XML elements.

Wildcard	Description
*	Match any element node
@*	Match any attribute node
Node ()	Match any type of Node

Instance

In the following table, we list some path expressions and the results of these expressions:

Path expression	Result
/Bookstore /*	Select All subnodes of the bookstore Element
//*	Select all elements in the document
// Title [@ *]	Select All title elements with attributes.

Select several paths

You can select several paths by using the "|" operator in the path expression.

Instance

In the following table, we list some path expressions and the results of these expressions:

path expression	result
// book/Title | // book/price	select the title and price elements of all book elements.
// Title | // price	select the title and price elements in all documents.
/bookstore/book/Title | // price	select the title element of all the book elements that belong to the bookstore element, and