XPath - Expression

An XPath expression generally defines a pattern in order to select a set of nodes. These patterns are used by XSLT to perform transformations or by XPointer for addressing purpose.

XPath specification specifies seven types of nodes which can be the output of execution of the XPath expression.

Root
Element
Text
Attribute
Comment
Processing Instruction
Namespace

XPath uses a path expression to select node or a list of nodes from an XML document.

Following is the list of useful paths and expression to select any node/ list of nodes from an XML document.

S.No.	Expression & Description
1	node-name Select all nodes with the given name "nodename"
2	/ Selection starts from the root node
3	// Selection starts from the current node that match the selection
4	. Selects the current node
5	.. Selects the parent of the current node
6	@ Selects attributes
7	student Example − Selects all nodes with the name "student"
8	class/student Example − Selects all student elements that are children of class
9	//student Selects all student elements no matter where they are in the document

Example

In this example, we've created a sample XML document, students.xml and its stylesheet document students.xsl which uses the XPath expressions under select attribute of various XSL tags to get the values of roll no, firstname, lastname, nickname and marks of each student node.

students.xml

<?xml version = "1.0"?>
<?xml-stylesheet type = "text/xsl" href = "students.xsl"?>
<class>
   <student rollno = "393">
      <firstname>Dinkar</firstname>
      <lastname>Kad</lastname>
      <nickname>Dinkar</nickname>
      <marks>85</marks>
   </student>
   <student rollno = "493">
      <firstname>Vaneet</firstname>
      <lastname>Gupta</lastname>
      <nickname>Vinni</nickname>
      <marks>95</marks>
   </student>
   <student rollno = "593">
      <firstname>Jasvir</firstname>
      <lastname>Singh</lastname>
      <nickname>Jazz</nickname>
      <marks>90</marks>
   </student>
</class>

students.xsl

<?xml version = "1.0" encoding = "UTF-8"?>
<xsl:stylesheet version = "1.0"
   xmlns:xsl = "http://www.w3.org/1999/XSL/Transform">  

   <xsl:template match = "/">
      <html>
         <body>
            <h2>Students</h2>
            <table border = "1">
               <tr bgcolor = "#9acd32">
                  <th>Roll No</th>
                  <th>First Name</th>
                  <th>Last Name</th>
                  <th>Nick Name</th>
                  <th>Marks</th>
               </tr>
               <xsl:for-each select = "class/student">
                  <tr>
                     <td> <xsl:value-of select = "@rollno"/></td>
                     <td><xsl:value-of select = "firstname"/></td>
                     <td><xsl:value-of select = "lastname"/></td>
                     <td><xsl:value-of select = "nickname"/></td>
                     <td><xsl:value-of select = "marks"/></td>
                  </tr>
               </xsl:for-each>
            </table>
         </body>
      </html>
   </xsl:template>

</xsl:stylesheet>

Verify the output