Rafe Colburn pointed to a blog posting by David Heinemeier Hansson where he that you should keep your business logic in your business layer rather than in your database which then lead to a blog post by Martin Fowler entitled Database Styles. Martin says he has only one principal point but he I think he made two good points. First (as he mentioned), there are generally two styles of databases: application databases (a database controlled and accessed by a single application) and integration databases (which acts as a data store for multiple applications) and that when you enter a discussion about THE ‘database’, you need to make it clear which type of database you’re talking about. His second point is that SOA (I’m not a fan of the acronym, but I like the implementations) can make and maybe should make integration databases unnecessary. Instead of having multiple applications interop through a common datastore (which is really nothing more than a gigantic global variable isn’t it?), each application maintains it’s own application database and communicates through a service interface like SOAP, REST, JMS, etc.

Rafe went on to make a good point as well (or maybe just a point that I agree with). He said that the one exception he makes to the rule of logic in the business layer rather than the database is the use of constraints. A commenter summed it up nicely by saying that “… constraints are to your data what assertions and tests are to your code.”