Use case diagrams provide a way of describing the external view of a system and its interactions with the outside world. Actors are a representation of the outside world, and can represent people or computer systems. A use case is a coherent unit of functionality provided by a system or class as manifested by sequences of messages exchanged within the system, and one or more outside interactors (the actors), along with actions performed by the system. A use case diagram depicts the relationship between actors and use cases within a system, as shown:
Related Topics:
Creating Browse-Through Sequences
Using Shortcuts in a Use Case Diagram