Object Model / Relational Technology

I have a vague memory of an interesting approach
to object-oriented databasing and now need to dig
deeper into it. The objects were stored in a plain-vanilla
RDBMS, what had all sorts of advantages. Now I would
like to read up on this approach before investing
design-work into my own project. Does anybody know
what the official term for this pattern is? Is there
a GPLed package that works like this? The unknown designer
of the thing made it work like this:

Classes, or object instances are sets of attributes.
An attribute can store a string, an int or a reference
to another object.

The attributes are themselves objects and store to
which object they belong. This way, nested hierarchies
of arbitrary complexity can be built. A tailer-made
engine stores objects and re-assembles them for the
client at run-time.

Ever heard of such a beast?