Michael Valentine Jones (10/14/2010)
Always use Surrogate keys for the primary key. Add unique constraints on all natural keys (alternate keys).
A primary key means exactly the same thing as an alternate key so as you've written it this advice doesn't make much sense. I expect you mean "avoid using business data in any foreign key references" but that's different. Anyway, using natural keys for foreign key references can be very useful, advantageous and sometimes necessary.