At a SGML user conference in The Hague last december, I had a talk with the people of Software AG and one of the questions was if Tamino wasn't just a SQL database with only memo fields.
They said that was making it to simple, but from their reaction I should say we weren't far off.
I don't see the advantage (yet) of a native xml database over a Oracle or MS SQL server database, which both support xml queries.
Jordi Reineman