>>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 ) ?

>>He must receive a message from the data tier, ok ?
>
>About what?

Your business tier must receive a message about customer deleting .

>
>>So who's handle it the data or the business tier ? :)
>
>Business tier.

Ok that's your choice
But what I mean is that the data tiers receive the message first and communicate to the business tier after.
So even when the business tier handle the RI, the delete trigger is send by the data tier.