Ah, well, you see, Markus...In that case I'm going to have many many more problems than an interface object knowing about PKs *rbg*. But actually, my (rather dull) point was not that the business tier should control pks, but surely it can *know* about them. (I'm trying learn here, not pick a fight.)

I've got a hodgepodge of bits and pieces that drive me nuts if I think about it too much! So, mostly one side of my brain tries to absorb all the *right* things while the other tries to stay billable ;-)

okay my brain is going to explode, now :-)

>Well, the problem I have with the middle-tier knowing about PKs is as follows: What if you decide to switch to a back end that's architecture is totally different and doesn't support primary keys, or that does primary keys totally different (such as in a scenario where you have to talk to data that's not yours...).