This is part four of my series on [[Physical Data Modeling AntiPatterns Series|Physical Data Modeling AntiPatterns]].
If you want to store data in XML for any (valid) reason, then by all means, do so. But if you are storing your data in XML in the RDBMS then I really question your design. There are many reasons to store data in XML (ease of interchange for instance), but if you also need to query that data (also known as shredding) then you need to re-evaluate the design. Yes, most RDBMS provide robust querying capabilities for declared XML data types. I've written tons about the performance implications of storing [[XML|XML in the database]]. If you need to query data, store it in a table. If you still need the XML representation then point to that from your data that is properly stored in your RDBMS tables.