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Friday, August 13, 2010

The XML Example


Selecting Nodes

XPath uses path expressions to select nodes in an XML document. The node is selected by following a path or steps. The most useful path expressions are listed below:
ExpressionDescription
nodenameSelects all child nodes of the named node
/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
In the table below we have listed some path expressions and the result of the expressions:
Path ExpressionResult
bookstoreSelects all the child nodes of the bookstore element
/bookstoreSelects the root element bookstore
Note: If the path starts with a slash ( / ) it always represents an absolute path to an element!
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



Predicates

Predicates are used to find a specific node or a node that contains a specific value.
Predicates are always embedded in square brackets.
In the table below we have listed some path expressions with predicates and the result of the expressions:
Path ExpressionResult
/bookstore/book[1]Selects the first book element that is the child of the bookstore element.
Note: IE5 and later has implemented that [0] should be the first node, but according to the W3C standard it should have been [1]!!
/bookstore/book[last()]Selects the last book element that is the child of the bookstore element
/bookstore/book[last()-1]Selects the last but one book element that is the child of the bookstore element
/bookstore/book[position()<3]Selects the first two book elements that are children of the bookstore element
//title[@lang]Selects all the title elements that have an attribute named lang
//title[@lang='eng']Selects all the title elements that have an attribute named lang with a value of 'eng'
/bookstore/book[price>35.00]Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00
/bookstore/book[price>35.00]/titleSelects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00

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