Apache: The Definitive Guide, 3rd Edition

XML, XSLT, and Web Applications

Extensible Markup Language (XML) has taken off in the last few years as a generic format for storing information. XML looks much like HTML, with a similar combination of elements and attributes for marking up text, but it lets developers create their own vocabularies. Some XML is shared directly over the Web; some XML is used by web services applications; and some XML is used as a foundation for web sites that need to present information in multiple forms. Serving XML documents is just like serving any other files in Apache, requiring only putting the files up and setting a MIME type identifier for them. Web services generally require the installation of modules specific to a particular web-service protocol, which then act as a gateway between the web server and application logic elsewhere on the computer.

The last option — using XML as a foundation for information the Apache server needs to be able to present in multiple forms — is growing more common and fits well in more typical web-server applications. In this case, XML typically provides a format for storing information separate from its presentation details. When the Apache server gets a request for a particular file, say in HTML, it passes it to a tool that deals with the XML. That tool typically loads the XML document, generates a file in the format requested, and passes it back to Apache, which then transmits it to the user. (The XML processor may pull the file from a cache if the file has ...