Use-case diagrams

Use-case diagrams describe the high-level functions and scope of a system. These diagrams also identify the interactions between the system and its actors. The use cases and actors in use-case diagrams describe what the system does and how the actors use it, but not how the system operates internally.

Use-case diagrams illustrate and define the context and requirements of either an entire system or the important parts of the system. You can model a complex system with a single use-case diagram, or create many use-case diagrams to model the components of the system. You would typically develop use-case diagrams in the early phases of a project and refer to them throughout the development process.

Use-case diagrams are helpful in the following situations:

• Before starting a project, you can create use-case diagrams to model a business so that all participants in the project share an understanding of the workers, customers, 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 the analysis and design phases, you can use the use cases and actors from your use-case diagrams to identify the classes that the system requires.
• During the testing phase, you can use use-case diagrams to identify tests for the system.

The following topics describe model elements in use-case diagrams: