Debugging XML Applications
By Michael Floyd
When developing XML applications, it's often necessary to use several technologies to manage data. As a developer, you must first design schema to represent the data, use markup to describe it, DTDs to validate it, XSL to transform and present it, and the DOM to access and modify it programmatically. In a client-server arrangement, you also have to deal with the technologies of the existing infrastructure.
Because there are so many factors in a single XML application, it's not always easy to tell where things went wrong when a document doesn't display correctly. This is particularly true when generating XML dynamically from a server, because you never see the XML that's being generated. It's possible to spend hours debugging the program. So what can you do to locate the problem quickly and solve it?
Debugging Strategies
Debugging a static XML document is relatively straightforward. All you need do is run the document through a parser, which will show you where there are formatting errors. However, when debugging applications that generate XML on the fly, your chances of finding the errors in the document are slim. Because the document lives (and dies) in memory, you never actually get to see the XML that's being generated. There's no physical XML file to run through a parser.
In this case—actually, in any case—the first thing you want to do is ensure that your XML document is well formed. If the data being generated isn't well formed, the parser fails to generate any output, and if your application is supposed to produce a resulting HTML document you'll typically end up with a blank screen instead.
