Role Interface

The strength of a role interface is that it clearly communicates the actual collaboration between an activity and its successors. Often a class doesn't use all the methods of a class, so it's good to show which ones are actually needed. This can be particularly useful if you need to substitute it later on. A header interface forces you to implement every method, even if you're not going to need them; but with a role interface you only need to implement exactly what's needed.

http://martinfowler.com/bliki/RoleInterface.html