If all interaction with a system is described in terms of procedures written as use cases, then the Use Case Model provides a complete, black-box, outside-in view of system functionality. The Use Case Model is not intended to be an exhaustive definition of system functionality - that only comes with a full internal system model that results from a detailed system analysis. The Use Case Model rather serves to scope the system functionality by defining what functions will or will not be performed by the system in sufficient detail that we can be sure we haven't missed anything important. The Use Case Model consists of:

	Actors, Use Cases and their relationships which appear on
	A number of Use Case Diagrams which together cover all of the proposed system functionality and are supported by
	Use Case Documents, written largely in text, which describe the detail of the flow of each use case and supported by and consistent with
	Optional Prototype Screens or Human Interfaces and
	Optional Activity Diagrams