Introduction to XPath

Introduction to XPath - Getting Elements
(Page 3 of 4 )

You can use indexing of elements to give you results similar to arrays. The /book expression selects both <book> elements. To get the first <book> element use /book[1]. Similarly, for the second <book> element use /book[2] or/book[last()]. The last() function identifies the last element.

/book[last()]

<bookstore>
  <book>
    <title id='1'>XPath Tutorial</title>
    <author>Mamun Zaman</author>
    <year>2007</year>
    <price>00.99</price>
  </book>
  <book>
    <title id='2'>AJAX Tutorial</title>
    <author>Charles</author>
    <year>2007</year>
    <price>03.45</price>
  </book>
</bookstore>

Attributes are specified by the @ prefix. The /book/title/@id expression selects only the attribute as mentioned below.

<bookstore>
  <book>
    <title id='1'>XPath Tutorial</title>
    <author>Mamun Zaman</author>
    <year>2007</year>
    <price>00.99</price>
  </book>
  <book>
    <title id='2'>AJAX Tutorial</title>
    <author>Charles</author>
    <year>2007</year>
    <price>03.45</price>
  </book>
</bookstore>

//B[@id] selects B elements which have the id attribute in the following XML.

  <A>
          <B id = "b1"/>
          <B id = "b2"/>
          <B name = "bname"/>
          <B/>

  </A>

//B[@id='b1'] selects B elements which have the id attribute with a value of b1.

     <A>
          <B id = "b1"/>
          <B name = " xyz "/>
          <B name = "bbb"/>
     </A>

The name() function returns the name of the element. Some other functions for selections are starts-with() and contains(). The //*[starts-with(name(),'B')] expression selects all elements whose names start with 'B'. The//*[contains(name(),'C')] expression selects all elements whose names contain 'C'. The string-length() function returns the length of the input string. The //*[string-length(name())>5] expression selects all the elements whose names are five or more letters long.

Several paths can be combined with the pipe ( | ) separator. The //year | //price expression selects all year and price elements.

<bookstore>
  <book>
    <title id='1'>XPath Tutorial</title>
    <author>Mamun Zaman</author>
    <year>2007</year>
    <price>00.99</price>
  </book>
  <book>
    <title id='2'>AJAX Tutorial</title>
    <author>Charles</author>
    <year>2007</year>
    <price>03.45</price>
  </book>
</bookstore>

To find a node of type text use the text() function. To get the year value use //year/text().

<bookstore>
  <book>
    <title id='1'>XPath Tutorial</title>
    <author>Mamun Zaman</author>
    <year>2007</year>
    <price>00.99</price>
  </book>
  <book>
    <title id='2'>AJAX Tutorial</title>
    <author>Charles</author>
    <year>2007</year>
    <price>03.45</price>
  </book>
</bookstore>

XPath defines four data types: node-sets, strings, numbers and Booleans.

The available operators are:

• The "/", "//" and "[...]" operators, used in path expressions=.
• A union operator, "|", which forms the union of two node-sets.
• Boolean operators "and" and "or", and a function "not()"
• Arithmetic operators "+", "-", "*", "div" (divide), and "mod"
• Comparison operators "=", "!=", "<", ">", "<=", ">="

The function library includes:

• Functions to manipulate strings: concat(), substring(), contains(), substring-before(), substring-after(), translate(), normalize-space(), string-length()
• Functions to manipulate numbers: sum(), round(), floor(), ceiling()n>
• Functions to get properties of nodes: name(), local-name(), namespace-uri()
• Functions to get information about the processing context: position(), last()
• Type conversion functions: string(), number(), boolean()

Some of the more common and useful functions are detailed in the next section. For a complete description, see the W3C Recommendation document. W3Schools also has some nice XPath articles.

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