There's one approach to OO databases which is seems interesting to me. It's called SBA (Stack Based Approach) and the corresponding query language is called SBQ

There's one approach to OO databases which is seems interesting to me. It's called SBA (Stack Based Approach) and the corresponding query language is called SBQL. It's been a subject of academic research in Poland for quite a while now, they've published a number of papers and a book on the subject, but only recently they actually got to implementing the thing. The project's web page is http://loxim.mimuw.edu.pl/ http://loxim.mimuw.edu.pl/ It is still rather immature and the English documentation is definitely incomplete, but in my opinion there is a (small) chance that this could grow into something big and useful.