July 2, 2008
@ 01:56 PM

Jeff Atwood recently published two anti-XML rants in his blog entitled XML: The Angle Bracket Tax and Revisiting the XML Angle Bracket Tax. The source of his beef with XML and his recommendations to developers are excerpted below

Everywhere I look, programmers and programming tools seem to have standardized on XML. Configuration files, build scripts, local data storage, code comments, project files, you name it -- if it's stored in a text file and needs to be retrieved and parsed, it's probably XML. I realize that we have to use something to represent reasonably human readable data stored in a text file, but XML sometimes feels an awful lot like using an enormous sledgehammer to drive common household nails.

I'm deeply ambivalent about XML. I'm reminded of this Winston Churchill quote:

It has been said that democracy is the worst form of government except all the others that have been tried.

XML is like democracy. Sometimes it even works. On the other hand, it also means we end up with stuff like this:

<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" 
    <m:GetLastTradePrice xmlns:m="Some-URI">

You could do worse than XML. It's a reasonable choice, and if you're going to use XML, then at least learn to use it correctly. But consider:
  1. Should XML be the default choice?
  2. Is XML the simplest possible thing that can work for your intended use?
  3. Do you know what the XML alternatives are?
  4. Wouldn't it be nice to have easily readable, understandable data and configuration files, without all those sharp, pointy angle brackets jabbing you directly in your ever-lovin' eyeballs?

I don't necessarily think XML sucks, but the mindless, blanket application of XML as a dessert topping and a floor wax certainly does. Like all tools, it's a question of how you use it. Please think twice before subjecting yourself, your fellow programmers, and your users to the XML angle bracket tax. <CleverEndQuote>Again.</CleverEndQuote>

The question of if and when to use XML is one I am intimately familiar with given that I spent the first 2.5 years of my professional career at Microsoft working on the XML team as the “face of XML” on MSDN.

My problem with Jeff’s articles is that they take a very narrow view of how to evaluate a technology. No one should argue that XML is the simplest or most efficient technology to satisfy the uses it has been put to today. It isn’t. The value of XML isn’t in its simplicity or its efficiency. It is in the fact that there is a massive ecosystem of knowledge and tools around working with XML.

If I decide to use XML for my data format, I can be sure that my data will be consumable using a variety off-the-shelf tools on practically every platform in use today. In addition, there are a variety of tools for authoring XML, transforming it to HTML or text, parsing it, converting it to objects, mapping it to database schemas, validating it against a schema, and so on. Want to convert my XML config file into a pretty HTML page? I can use XSLT or CSS. Want to validate my XML against a schema? I have my choice of Schematron, Relax NG and XSD. Want to find stuff in my XML document? XPath and XQuery to the rescue. And so on.

No other data format hits a similar sweet spot when it comes to ease of use, popularity and breadth of tool ecosystem.

So the question you really want to ask yourself before taking on the “Angle Bracket Tax” as Jeff Atwood puts it, is whether the benefits of avoiding XML outweigh the costs of giving up the tool ecosystem of XML and the familiarity that practically every developer out there has with the technology? In some cases this might be true such as when deciding whether to go with JSON over XML in AJAX applications (I’ve given two reasons in the past why JSON is a better choice).  On the other hand, I can’t imagine a good reason to want to roll your own data format for office documents or application configuration files as opposed to using XML.

  • The XML Litmus Test - Dare Obasanjo provides some simple guidelines for determining when XML is the appropriate technology to use in a software application or architecture design. (6 printed pages)
  • Understanding XML - Learn how the Extensible Markup Language (XML) facilitates universal data access. XML is a plain-text, Unicode-based meta-language: a language for defining markup languages. It is not tied to any programming language, operating system, or software vendor. XML provides access to a plethora of technologies for manipulating, structuring, transforming and querying data. (14 printed pages)

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