XSLT `xsl:key` Element: Creating Keys for Efficient Node Selection in XML Transformations

Learn how to use XSLT's `xsl:key` element to create keys for efficient node lookup in your XML transformations. This tutorial demonstrates defining keys and using the `key()` function in XPath expressions for faster and more efficient selection of specific nodes based on defined values.

Using the XSLT `xsl:key` Element

The XSLT `xsl:key` element is used to define a key that associates a value with a node in the XML document. This key can then be used with the `key()` function in XPath expressions to efficiently locate specific nodes. This is a powerful mechanism for creating indexes within your XML data, enabling faster access to specific elements.

`xsl:key` Element Syntax and Attributes


<xsl:key name="keyName" match="pattern" use="xpath_expression"/>

The attributes are:

  • name: The name of the key. This name is used to refer to the key in XPath expressions using the `key()` function.
  • match: An XPath pattern that specifies which nodes the key is applied to.
  • use: An XPath expression that determines the key's value (what will be used to identify the nodes).

Example: Creating a Key on Employee Names

(Note: This example requires an XML file named `employee.xml` and an XSLT stylesheet named `employee.xsl`. Screenshots from the original text are not included here. Please refer to the original document for visual verification of the example and XSLT output. The descriptions below aim to convey the information present in those screenshots.)

This example demonstrates creating an XSLT key to find employees by their first name. The XML data would be in an `employee.xml` file, and an XSLT stylesheet (`employee.xsl`) would use this key to select and display employee data.

`employee.xml` (Example XML Data)


<employees>
  <employee>
    <firstName>Aryan</firstName>
    <lastName>Gupta</lastName>
    <nickName>Raju</nickName>
    <salary>60000</salary>
  </employee>
  <!-- ... more employee elements ... -->
</employees>

`employee.xsl` (XSLT Stylesheet)

(The original content includes the content of the `employee.xsl` file. Since we cannot display the file here, please refer to the original document for the file content.)

Test it Now

(The original content includes a screenshot showing the output. Since we cannot display images, please refer to the original document for the visual representation of the output.)

The output demonstrates that the XSLT successfully retrieves and displays the employee details using the key created for efficient searching.