Remember the thrill of watching your first HTML form work? Perhaps you simply e-mailed the contents of the form to yourself or displayed another HTML page with whatever information the user entered. Whatever you did, you created what an information architect would call a two tiered or client/server system. With just a little additional work, the input gathered from a Web form can be stored in a database. In this way, multiple clients can interact with a single database using only their browser. The information stored in the database can be formatted into an appropriate HTML display on demand by CGI scripts. A typical Web application that uses this sort of architecture is a Weblog like SlashDot (see Resources). The code that generates the HTML page is called the front end and the part that contains the database and business logic is called the back end.

This system works very well until either your database or your Web server can no longer handle the traffic. If the bottleneck lies with your Web server, you may decide to simply add more Web machines to your network. If you connect to your database with native Application Programming Interface (API) calls in your front end, it becomes difficult to change the back end implementation. Switching database vendors or trying to cluster the database servers would mean changing all your front end code. The solution is to separate the presentation logic of the front end from the business logic of the back end, but they still need to be connected. The software that provides the conduit between the front end and the back end is called middleware. And one very simple, open architecture middleware protocol that works well in Web applications is XML-RPC.

In this article we'll show you how to turn your HTML files into mini databases by embedding XML tags within your Web pages to describe the enclosed content. We'll then build a Web-based Perl client that queries and displays the contents of these embedded XML tags. Finally, we'll extend what we've learned by developing a script that builds a top-news summary for http://www.internetnews.com.

The introduction and adoption of XML, a simplified version of SGML, is poised to make a monumental, yet fundamental advancement in how we store, share, and interact with data. Thanks in part to its simplicity, the Web has created a global information revolution that has redefined communication and human interaction. As a result, these global information repositories on the Web are becoming large and unmanageable. Even worse, HTML does not contain methods for organizing or classifying data. This makes it difficult for users to find pertinent information.

XML, on the other hand, is capable of independently defining and describing data in an easy to understand human and machine readable format. This frees the data from proprietary formats, which limit the scope, effectiveness, and longevity of information.

But how can we use XML in our sites today? After all, HTML is incompatible with XML. Read on and you'll find out