Diagramming Use Cases


Of all the diagrams in UML, use case diagrams are the most confusing and the least useful. I recommend that you avoid them entirely, with the exception of the system boundary diagram.

Figure 17-1 shows a system boundary diagram. The large rectangle is the system boundary. Everything inside the rectangle is part of the system under development. Outside the rectangle are the actors that act on the system. Actors are entities outside the system and provide the stimuli for the system. Typically, actors are human users. They might also be other systems or even devices, such as real-time clocks.

Figure 17-1. System boundary diagram


Inside the boundary rectangle are the use cases: the ovals with names inside. The lines connect the actors to the use cases they stimulate. Avoid using arrows; nobody really knows what the direction of the arrowheads means.

This diagram is almost, but not quite, useless. It contains very little information of use to the programmer, but it makes a good cover page for a presentation to stakeholders.

Use case relationships fall into the category of things that "seemed like a good idea at the time." I suggest that you actively ignore them. They'll add no value to your use cases or to your understanding of the system and will be the source of many never-ending debates about whether to use «extends» or «generalization».




Agile Principles, Patterns, and Practices in C#
Agile Principles, Patterns, and Practices in C#
ISBN: 0131857258
EAN: 2147483647
Year: 2006
Pages: 272

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