Read Conway's Object Oriented Perl, for a million reasons, but specifically because it has a chapter showing how to achieve coarse and fine-grain persistance with all the serialization packages out there and with databases.
It should answer your questions a lot better than I could.
-pete
Entropy is not what is used to be.
Comment on Re: Need a module for persistence of dynamic objects
I second this suggestion. Every time I read something in Conway's book and had a question, it would almost always be answered in the next section or chapter. It's also worth the buy for the investigation into class creation modules, too.