Composing requirements for goal-oriented system behaviors using an extended form of use case

Use cases have been shown to be an effective construct to express system requirements in terms of environmentally visible behaviors. However, refinement of the use case into a set of corresponding system requirements is only indirectly supported by use case semantics that focus on environmental objects and their interaction with the system. The authors use a scenario-like extension to the actor-oriented use case called a system-oriented use case which extends the use case to a set of system behaviors. We enrich the system-oriented use case with a fusion-like notation to encode the specification of system behaviors constrained by the actor's role and in support of the actor's goal. Our extensions produce incrementally less abstract requirements that terminate in life cycle expressions traceable to the use case and actor. We provide formal definitions for role, goal and the responsibilities of liveness and safety.