14.2. An Introduction to XML

XML is useful because it provides an industry standard way of describing data. In addition, XML accomplishes this feat in a style similar to HTML, which thousands of developers are already familiar with. CGI programs that speak XML will be able to deliver to and retrieve data from any XML-compliant Perl script or Java applet.

It is possible to use CGI as middleware without a data description language such as XML. The success of libraries such as LWP for Perl demonstrates this. However, most web pages still deliver data as plain HTML. Using LWP to grab these pages and the HTML::Parser to parse them leaves much to be desired. Although HTML has to be produced in order for a web browser to consume the data even when XML is used, the HTML itself is likely to change depending on how the web designer wants the page to look, even if the data described in XML would still remain the same. For this reason, writing a parser for an HTML document can be problematic because the HTML parser will break as soon as the structure of how the data is displayed is changed.