True business logic has only one place, and that's the database. Databases are designed to be shared amongst applications across an enterprise, and to be the final arbiter of good and bad data. Why do developers insist that logic should be duplicated (re-programmed!) again and again whenever a new application is created? If something is truly a business rule -- and not an application rule -- that logic belongs in the database, where it can be constrained properly, exactly once.