>Of course you could create a separate 'logical' data tier in code to handle this type of thing. You could create your own data objects and place your appropriate code there depending on the backend type. Probably some would do that. It adds another level to maintain though but would work as well.

This is what my framework does. I have a Data Manager baseclass separate from my Business Object baseclass. Data Managers are subclassed to work with specific groupings of parent/child tables and the RI code is included in these subclasses.

I went with this strategy not only in order to be able to use different back ends, but also on the assumption that I might someday want to write my own server, which would use these data classes internally and pass data to client software that encompasses the business objects (and GUI).