25.2. Terminology: Concrete, Abstract, Base, and Addition Use Cases

A concrete use case is initiated by an actor and performs the entire behavior desired by the actor [RUP]. These are the elementary business process use cases. For example, Process Sale is a concrete use case. By contrast, an abstract use case is never instantiated by itself; it is a subfunction use case that is part of another use case. Handle Credit Payment is abstract; it doesn't stand on its own, but is always part of another story, such as Process Sale.

A use case that includes another use case, or that is extended or specialized by another use case is called a base use case. Process Sale is a base use case with respect to the included Handle Credit Payment subfunction use case. On the other hand, the use case that is an inclusion, extension, or specialization is called an addition use case. Handle Credit Payment is the addition use case in the include relationship to Process Sale. Addition use cases are usually abstract. Base use cases are usually concrete.