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Apache Web Server: Article

XML Heaven or XML Hell?

Why anti-XML sentiment is misguided

"With proper markup/logic separation, a POJO data model, and a refreshing lack of XML..." So begins the introduction to one of the current crop of open source Web application frameworks on its Web site. Sadly this seems to be a common sentiment within the Java framework development community; the phrase "XML Hell" is thrown around with the same vehemence once reserved for the "DLL Hell" so characteristic of early versions of Microsoft Windows. Is this wisdom genuine or apocryphal? In this article I will examine some of the reasons why anti-XML sentiment is misguided.

The Roots of the Myth
Where does this distaste for XML in the Java framework development community come from? Several factors immediately spring to mind.

First of all, XML's lack of tooling support is a significant issue. Let's use the XML-driven framework Apache Struts as an example. Though popular, Struts is often held up as an illustration of how XML-configured frameworks are bad (although many making this claim are competitors of Struts). In reality, I think the problem has nothing to do with XML; rather it's the fact that the Struts page-flow metadata represents a series of complex relationships. Of course the raw XML that describes these relationships is hard to understand, but that's not really a problem with the XML itself. Any textual description of a page flow, in code or metadata, is hard to understand. Put that same relationship map into the form of a diagram and the problem goes away. Indeed when mainstream development environments such as Oracle JDeveloper and Eclipse started to provide visual diagramming for Struts, the framework's popularity skyrocketed. An inability to understand something often translates into dislike - perhaps XML has been the innocent bystander in a bigger battle against perceived complexity.

Overuse also adds to the negative perception of XML. While great for describing complex relationships, XML can be viewed as overkill for simple framework configuration. Enterprise JavaBeans (EJB) are often held up as an example of how badly XML can be overused. Interestingly one of the key features of the latest version of the EJB specification (3.0) addressed the issue head on. In the latest version, although XML metadata is still a valid option for describing the entities, code annotations and "configuration by exception" are the norm for describing simpler relationships. XML is only used for the corner cases.

Are Annotations the Future?
After EJB adopted annotations as a configuration option, the floodgates opened and annotations seemed to be the one true path to framework configuration. New annotation-based frameworks such as Seam were developed, and old frameworks such as Struts were hastily retrofitted in a misguided attempt to gain favor.

More Stories By Duncan Mills

Duncan Mills is senior director of product management for Oracle's Application Development Tools - including the JDeveloper IDE, and the Oracle Application Development Framework. He has been in the IT industry for the past 19 years working with Oracle, Java, and a variety of more obscure programming languages and frameworks along the way. Duncan is the co-author of the Oracle Press book: Oracle JDeveloper 10g for Forms and PL/SQL Developers - a Guide to Web Development with Oracle ADF.

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Most Recent Comments
hkara 11/25/08 11:36:20 AM EST

Well, there is truth in this article, but there is
also truth in the developers that speak of
"XML hell". XML is great when computers speak to
computers, and it was made in great part for that :
to quickly write reliable and fast parsers for
structured documents. Unfortunately, just like when
Tim Berners Lee never thought that people would
actually *write* html using text editors, people
started writing xml with text editors.
Why ? Because there's nothing else, most of the
time. Imagine what would have happened if XML had
existed when relational databases were invented...
Imagine expressing SQL queries in XML (this actually
exists, but it's for machines).

When people are not in contact with XML directly,
XML isn't a problem. When we edit an SVG document
in Inkscape, when I change my preferences in Eclipe,
I use an XML document, but through a specialized
user interface that does not make the whole thing
cumbersome and painful. Yet the documents produced
have all the advandages of XML : portability, reliability, ease of parsing, etc. So I guess the
problem is more : how easy is it to configure the
system ? If you have to edit XML directly, chance
are that this is difficult. It may be powerful,
portable, etc, but it is still difficult.
I agree that annotations are not the right thing.
For me, the right thing is either a specialized
language using an LL or LR parser, or a specialized
editor that manipulates the XML for the user.

Besides that, I think that your article is hitting the right point.

Best regards,

Harry