I'm trying to rewrite my app using the 3 Tiers architecture..

and my friend and I are argumenting about the following fact:

one of us say:

GUI -> Business -> Data


and the other says:

GUI -> Data -> Business

Which one is the correct way of designing 3 tiers architecture?


And would it be correct to say in both case that it is more likely to have the same class (let's say a user class) for both Biz and Data layer.. and Biz will validate properties/input before data puts it in a DB ?


Thanks