J2EE Design Patterns

Use Case Diagrams

A use case diagram is the highest level of abstraction available in UML. Use cases are collections of related activities that work toward a particular goal. They’re part of the requirements gathering process rather than the design process itself, and can be as detailed or as generic as is necessary to communicate system requirements.

The challenge here is often to make the requirements accessible and useful to both the design team and the domain experts involved in the project. Depending on need, the size of the team and the preferences of those leading the development a project might have two or three use cases, or dozens, or even more, although there is generally a point at which the sheer volume of use cases grows unmanageable.

A “Buy Groceries” use case, for example, could consist of selecting food, checking out, processing a credit card, and bagging groceries. The use case can also incorporate internal variations, such as a declined credit card.

Use cases incorporate multiple actors , which may be humans or systems. The actors in the Buy Groceries use case could be the shopper, the checkout person, the grocery bagger, the inventory system, and the credit processor.

Like any UML diagram, use cases exist to convey information. A use case diagram can be a valuable communication tool, and the process of creating the use cases themselves almost invariably leads to better software and greater accountability. In addition to ensuring user needs are met, use cases help ...