Reference Data Values

Suppose that you want to display your company information and sales data in a format that is more readable than the default tree view in Internet Explorer. You can do this by creating the following XSLT file, Transform.xsl. This file transforms the heading data values in the Sales.xml file into a well structured HTML format. The basic operations involve retrieving the data values of the specified elements or attributes. In XSLT, you use XPath pattern matching to do this. This is illustrated in Transform.xsl by use of the match and select attributes of the xsl:template and xsl:value-of elements, respectively. Notice how XPath expressions are constructed, in bold below, to reference element content and an attribute value.

To create the Transform.xsl file

Use your HTML or text editor to create a new file. Copy the following code into that file.

<?xml version='1.0'?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   <xsl:output method="html"/>
   <xsl:template match="/">
      <html>
         <head>
            <!-- Referencing a data value as element content: -->
            <title><xsl:value-of select="//summary/heading"/></title>
         </head>
         <body>
            <h1><xsl:value-of select="//summary/heading"/></h1>
            <h2><xsl:value-of select="//summary/subhead"/></h2>
            <p><xsl:value-of select="//summary/description"/></p>    

            <DIV>
                 Region: <xsl:value-of 
                         select="//data/region[1]/name"/>
            </DIV>

            <!-- Referencing a data value as an attribute value: -->
            <DIV>
                 First quarter sales: <xsl:value-of 
              select="//data/region[1]/quarter/@books_sold[1]"/>
            </DIV>
         </body>
      </html>
   </xsl:template>
</xsl:stylesheet>

In the same folder in which you saved the Sales.xml file, save the current file as Transform.xsl.

To specify the XSLT file to use with the XML file

In your HTML or text editor, open the Sales.xml file (if not already opened).
Locate the following code:
```
<?xml version="1.0"?>
```
After this line, add the following code:
```
<?xml-stylesheet type="text/xsl" href="transform.xsl"?>
```
This processing instruction identifies Transform.xsl as the XSLT file to be used for transforming Sales.xml.
Save and close Sales.xml.

To view the transformation results

In Internet Explorer, press F5 to refresh Sales.xml. This shows how Transform.xsl formats the data in the <summary> element, as well as the first quarter results of the West Region.
If you installed the Internet Explorer Tools for Validating XML and Viewing XSLT Output, you can also right-click in the Internet Explorer window and select View XSL Output from the pop-up menu.

How the Transform Works

At the beginning of Transform.xsl, the xsl:stylesheet line declares that this is an XSLT file. The xsl:output line tells the XSLT processor to produce HTML output instead of the default output method of "xml".

The xsl:template and xsl:value-of lines use the XPath expressions to pick out the content of an element and an attribute value. For example, <xsl:template match="/"> defines a template rule for the root element of the source XML document and all of its children. <xsl:value-of select="//summary/heading"/> returns the content of the <heading> element contained in the <summary> element. The <xsl:value-of select="//data/region[1]/quarter/@books_sold[1]"/> returns the value of the books_sold attribute for the first quarter in the first region, as ordered in the source document. The HTML tags format the retrieved data values.

Now you know how to select a given element, its content, or its attribute value. The next exercise shows how to Use CSS in XSLT.