Scott posted
A reminder on "Three/Multi Tier/Layer Architecture/Design" brought to you by my late night frustrations.
So, before writting DataLayer stuff in your .aspx page (or worse, open connections), please review the article. One interesting note. Usually due to lack of time, and need to deliver the product yesterday, communications between layers is made of datasets, which used properly are ok, but cannot be enforced easility to be read-only. So, beware of code that modifies datasets directly in your UI Layer.