>>>Think about two applications on the same back end. I delete a customer. How did your business tier handle this ?
>>
>>Uh, sensibly? Seriously, I don't understand your point. The business rule for deleting a customer would be invoked and as a part of that rule, there'd be a rule to go out and see if they have any invoices.
>>
>
>Your business tier is not in my application and my application delete a customer. ( or try to delete ).
>
>
>Your business tier handle the RI of the database, ok ( that's your choice ) ?
>

If you've done your analysis correctly, this will never happen because you'll learn how any current systems work. If one system does all it's data access via biz objects, you'd better find out what they do.