Business Logic: Database or Application Layer

Question

The age old question. Where should you put your business logic, in the database as stored procedures ( or packages ), or in the application/middle tier? And more importantly

Answer 1

While there is no one right answer - it depends on the project in question, I would recommend the approach advocated in "Domain Driven Design" by Eric Evans. In this approach the business logic is isolated in its own layer - the domain layer - which sits on top of the infrastructure layer(s) - which could include your database code, and below the application layer, which sends the requests into the domain layer for fulfilment and listens for confirmation of their completion, effectively driving the application.

This way, the business logic is captured in a model which can be discussed with those who understand the business aside from technical issues, and it should make it easier to isolate changes in the business rules themselves, the technical implementation issues, and the flow of the application which interacts with the business (domain) model.

I recommend reading the above book if you get the chance as it is quite good at explaining how this pure ideal can actually be approximated in the real world of real code and projects.