TABLE OF CONTENTS This chapter describes how to model the high-level functionality of a system with use cases.
Use cases describe the functionality of a system in terms of how its users use that system to achieve their goals. The users and other interested participants of a system are described by actors, which may represent external systems or humans who use the system. Use cases have a textual and graphical description that may be further elaborated with detailed descriptions of their behavior, using activities, interactions, or state machines. The relationships between the system under consideration, its actors, and use cases are described on a use case diagram that shares many characteristics with a block definition diagram.
Different methodologies apply use cases in different ways [34]. For example, some methods require a use case description for each use case captured in text, which may include pre- and postconditions, and primary, alternative, and/or exceptional flows.
Use cases have been viewed as a mechanism to capture system requirements in terms of the uses of the system. SysML requirements can be used to more explicitly capture text requirements and establish relationships with use cases and other model elements (refer to Chapter 12 for a discussion on requirements). The steps in a use case description can also be captured as SysML requirements.
On a use case diagram, the frame represents a package or block, and the content of the diagram describes a set of actors and use cases and the relationships...
