text=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.