Okay, so you're saying that some OO devs designed this database like they would design an OO system? I've seen some absolutely --wonderful-- output from those situations. Confusion about is-a vs. has-a relationships and how the DBMS enforces such relationships. In one case, an online ordering (ecommerce) system was designed such that the products table had a foreign key to the line items table! End result: These guys were inserting fake orders every time they wanted to sell new products. And of course, there were duplicate products inserted with every order. Luckily, their volume was very low