Given the emptyness of that class for now I'm still not sure whether we want this abstract or as an interface.
If we keep it abstract we do need basic unit test infra for it as well, even if there is nothing to test.
I guess right now it doesn't make much difference... What is the idea behind this class? what shared code is it supposed to have?
If I would have an idea it wouldn't be empty :P
The only thing I can think of is a ways to handle multiple DAOs, but then again I couldn't think of a reasonable way to do that. Maybe data transformation helpers or some such
I thought about this and I'd say make this an Interface for now. When we need dedicated functionality in a Model class we can reevaluate what to do.