Extensible Stylesheet Language (XSL) is a technology closely related to XML which is used to transform XML data. XML file are used to set out the ground-rules for a given body of data and to describe the data itself. XSL allows us to take the original XML data and convert it into information which can be displayed in a web browser window or opened with a text editor. XSL can also be used to create an XML file which is a modified version of an original XML file.

When displaying XML elements in a browser window, the XSL elements which enable looping through an XML tree and decision-making really come into their own. One of the key methods used in XSL for looping through elements in an XML file is the the "For-each" element. This requires the "select" attribute to specify which element is to be used in the loop. The "For-each" element normally requires both an opening and a closing tag and any lines of markup placed between the opening and closing tags will be repeated each time the element specified in the "select" attribute is encountered in the XML file.

For example, let's say we have an XML file containing a list of companies and the addresses of their websites. Let's also say that the element which we will be targeting in the XSL "For-each" statement is called "company" and that, within each company element, we have a "name", "telephone" and "website" element. Before beginning our "For-each" loop, we could place the opening tag of an HTML "ul" element (an unordered or bulleted list).

Inside the "For-each" loop, we could output an HTML "li" element and, between its opening and closing tags, output the contents of the "name" and "telephone" elements from the XML file. The data in the "website" element in the input XML could be used to convert the "name" into a clickable link.

As regards the appearance of the data in the resulting HTML output, this would be controlled by a linked CSS file. CSS can be used to format the output in any way we desire, so our bulleted list can take on pretty much any appearance we care to give it.

The writer of this article is a developer and trainer with Macresource Computer Training, a UK IT training company offering XML, XSLT, XPATH, XQuery and XSL-FO training courses in London and throughout the UK.