You're absolutely right - that is what I'm doing. My only experience of OO is through Perl, so forgive me if my terminology is shaky.

When I said When each of these is loaded, they register their Type with the Object class so that any object can be retrieved using the parent class and blessed into the right package., I really meant that each sub class registers with the parent class, which I have called Object.

And which is, as you say, a factory class. It handles the auto-generated accessor methods, the required attribute checking when saving an object, loading, caching and saving objects etc.