I'm not totally sure what you are getting at, but are you suggesting that the business rules described in the example (that salesmen are limited to selling cert

I'm not totally sure what you are getting at, but are you suggesting that the business rules described in the example (that salesmen are limited to selling certain products for certain brands) is not realistic in a real-world car dealership? That might be true, since it is just a simple example intended to demonstrate a concept. If everybody can sell every product, obviously there is no reason to keep a list of who can sell what. You just keep a list of actual sales. But that is a question of designing the database to correspond to the business. It has nothing to do with the merits of any of the normal forms. The normal forms does put any requirements on your business rules.