This reply is late in coming, but here are some thoughts after maintaining DBM::Deep for about 2 years, in no particular order:

• SQL is relational - it's all about set theory. Set theory is great . . . until it's not. Look up Object-relational impedance mismatch. 90% of what most people do is object-oriented, not set-oriented. Heck, I'm a DBA and I still do most things object-oriented in my code.
• Your specific question is answered using grep.
• If you're interested, I started a project last year called Presto, based on DBM::Deep. It's still very much in its infancy, but the idea is that you can have a DBMS (built on top of DBM::Deep) that doesn't suffer from the O-R impedance mismatch. (Note: DBMS, not RDBMS). I'd love help with it, if you're interested.