Hats off and a standing ovation to Don! You are so right in everything you write in the article. Some comments to the other comments you have received so far:
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Hierarchal data is a pain to manage and administer but it's main advantage is speed. I've read that there are people out there who have databases so large that RDBMS technology struggles to perform all the overnight processing.
First of all, the primary function of a database is not speed, but integrity. Second, the relational model can not be blaimed for inefficient implementations of it. Performance is a determined by the physical implementation of a database, the relational model is purely logical.
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Because an XML document is usually a text file it can be read by almost any OS. Yes, other formats are faster but that limits cross platform compatibility.
Why would this limit cross platform compatibility? Any platform can read a text file, no matter how the contents of it is formatted. XML in itself have absolutely no advantage to say a csv-file, it is the fact that it has become a de-facto standard that makes people choose xml over any other formatting. But, as Don points out in his article, it is definitely not an entirely wise choice, it has several major drawbacks. But this is just speaking about xml as a format for transferring data. Regarding data management and using xml as a data storage, there is absolutely no advantage at all over a relational database.
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The data is a complex relational set and could not be distributed (In real time) any other way. We couldn't pass a series of CSV files for the related data, XML was the only way to go.
How can a hierarchical xml file store complex relational sets?
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I think the conclusion I draw is that XML data services using an RDBMS as a backend have their places and uses.
Yes, you are right, I wouldn't argue that this is entirely wrong, if you stay with using xml as a data transport between applications. But I think that even though Don (and I agree with him fully) does not believe xml to be the definitive answer, what he is really saying in this article (especially since it is actually published at a SQL Server specific site) is that xml has no place inside SQL Server. And that is a very important message! We as developers and DBAs can do our part by not using these features and by continuing to request more important features and functionality, especially a better implementation of the relational model.
I'll finish off by seconding the book recommandtions in the article. I guarantee you, when you've read these books you will not continue argumenting for xml.
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Chris Hedgate @ Apptus Technologies (http://www.apptus.se)