Use-Case Diagrams

A use-case diagram is a UML diagram that provides a high-level view of the behaviors in a system or in part of a system. Use case diagrams also identify users of a system and their interactions with the system. A use-case diagram can depict all or some of the use cases in a system.

The major behaviors of a system are specified with use cases. Use cases indicate that the behaviors exist and describe the value that the results give to users. They do not describe how the behaviors are implemented. The external users of the system are presented as actors. Actors present the different roles people, hardware, and other systems play when they interact with the system. In addition, connectors in use case diagrams identify the relationships between the model elements.

The use cases and actors in use-case diagrams describe a system from an outsider's perspective. They do not describe how the system operates internally.

Shapes and Connectors

A use-case diagram can contain shapes and connectors that represent:

• actors

• use cases

• access relationships

• association relationships

• dependency relationships

• directed association relationships

• extend relationships

• generalization relationships

• import relationships

• include relationships

Using Use-Case Diagrams

Use-case diagrams are helpful because they illustrate and define the context and requirements of either an entire system or important parts of it. Use-case diagrams also identify the interactions between the system and its various users. Use-case diagrams are usually developed in the early phases of a software project and used throughout the development process. Possible uses of use-case diagrams include the following:

• Before starting the software project, you can create use-case diagrams to model a business so that all participants in the software project share an understanding of the workers, customers, entities, and activities of the business.

• While gathering requirements, you can create use-case diagrams to capture the system requirements and to present to others what the system should do.

• During analysis and design, you can use the use cases and actors in existing use-case diagrams to identify the classes that are required by the system.

• During testing, you can use existing use-case diagrams to identify tests that should be performed on the system.

Related Topics

Working with Use-Case Diagrams

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