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Development tools for XML applications: do we need 3GL-like XML development environments? XML is object without source. There can be no development tools for XML until we find a way of creating source code.

Article Excerpt
"There's no such thing as an XML application." A strong statement, perhaps, but what do we mean when we talk about an XML application? Is a publishing system that relies on XML to do its work an XML application? Can we apply the term to a B2B marketplace where all the processes in a transaction can be defined by DTDs and all data flowing around the system is in XML? Is a content syndication system an XML application? Or a foreign exchange business line in an investment bank?

Typically, all of the above use XML extensively. But what do they have in common? And how do we "develop" these systems? Do we "develop" the XML parts, or do they fall out of the development of other parts? After all, XML isn't a programming language. XML applications are built in C++, Java, or Visual Basic (for example).

The Common Ingredient

The common ingredient in all XML applications is, of course, the XML. The data flowing around in the system is in an XML format. As such, I would argue that people don't currently develop XML applications. They develop software systems that use XML to achieve certain aims.

For example, XML is the glue in EAI (enterprise application integration), gluing together pieces of software that probably have nothing to do with XML. Publishing systems use XML to provide single-source to multiple-output formats, but the systems themselves aren't "developed" in XML, nor do they care very much how the XML has been defined. Publishing systems are usually built using a combination of technologies that can store, communicate, and manipulate XML, but that aren't intrinsically XML technologies.

Why Do We Need XML Application Development Tools?

Why do we care about XML application development? We care because putting an industrial-strength XML-based application together is complex and error-prone. The veterans of this industry will say that they do everything in vi or Notepad -- and the implication is that development tools don't add much value, and perhaps can't even be trusted.

Explosion of Complexity

I disagree. XML allows you to develop sophisticated systems very rapidly, even if you do it all in vi (presuming you're working with a clean sheet). But once the system starts to take shape, you need help in the form of powerful software to build the XML pieces. This is because when you choose to use XML in your application, you're effectively taking single objects that are important to your organization, such as a Transaction ID, and referring to them in dozens, hundreds, or even thousands of places by the time you've put the system together (see Figure 1).

[FIGURE 1 OMITTED]

This is denormalization to a dangerous degree. The Transaction ID will find its way into schema fragments, be passed to Java classes, be described in stylesheets, be transformed by XSLT, and so on. Clearly, unless you get it right the first time...

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