>But the POV I expressed in an earlier message refutes that. RI is only necessary for logical validity, not physical data integrity. For example, an orphaned invoice is *only* a problem from our perspective of trying to use it.
It does not damage the data in any way.

Why did you handle data if you don't use it ?

>Also, RI depends too much on the back end store, and as we look at all the possibilities for backends that get's opened up by using n-tier...well, it seems clear to me that RI belongs in the business tier.

Think about two applications on the same back end. I delete a customer. How did your business tier handle this ?
He must receive a message from the data tier, ok ?
So who's handle it the data or the business tier ? :)