Use Case Diagrams

Use cases are useful to document but they do not stand-alone. There are relationships that need to be described between the use cases and the actors. UML describes a relationship between an Actor and a Use Case as an Association. An association can be navigated in one direction (actor to use case or use case to actor) or bi-directionally (actor to use case and use case to actor). The direction represents who is initiating communication. A single line represents an association between an actor and a use case. If communication travels in only one direction, then an arrowhead is added to the line. In this example, a unidirectional association from the actor to the use case is represented:

 

 

A use case diagram contains some or all of the actors and use cases and their interactions defined for a system. A model for a system should have an Architecturally Significant Use Case Diagram and possibly other less significant diagrams. Using our example, the following diagram could be drawn.