In a post entitled My comments on the Infoworld article "Databases flex their XML" Michael Rys writes
Sean McCown wrote this analysis (PDF version) in Apr 2004. In the article, he compares the XML capabilities of the 4 major relational database systems (comparing publicly available versions) both in terms of functionality, ease, flexibility and speed, and adds a sidebar on Yukon. Before I start giving my comments on the article, let me disclose that I talked to Sean during his research for the article and answered his questions on SQL Server 2000 and Yukon. Thus, some of the comments below are just my attempts to make Sean's translation of my answers clearer, because I was not answering his questions clear enough :-).
Michael then goes on to clarify various points around the terminology used in the article, XQuery and SQL Server. Both Sean's article and Michael's followup are excellent reading for anyone interested in the growing trend of XML-enabled relational databases and how the big 3 relational database vendors stack up.