Use Case diagram:
Use case diagrams describe what a system does from the standpoint of an external observer. The emphasis is on what a system does rather than how
Use case diagrams are closely connected to scenarios. A scenario is an example of what happens when someone interacts with the system
Let’s take an example of a medical clinic:
“”A patient calls the clinic to make an appointment for a yearly checkup. The receptionist finds the nearest empty time slot in the appointment book and schedules the appointment for that time slot. “”
A use case is a summary of scenarios for a single task or goal. An actor is who or what initiates the events involved in that task. Actors are simply roles that people or objects play. The picture below is a Make Appointment use case for the medical clinic. The actor is a Patient. The connection between actor and use case is a communication association (or communication for short).
Actors are stick figures. Use cases are ovals. Communications are lines that link actors to use cases.
A use case diagram is a collection of actors, use cases, and their communications. We’ve put Make Appointment as part of a diagram with four actors and four use cases. Notice that a single use case can have multiple actors.
Use case diagrams are helpful in three areas.
- Determining features (requirements). New use cases often generate new requirements as the system is analyzed and the design takes shape.
- Communicating with clients. Their notational simplicity makes use case diagrams a good way for developers to communicate with clients.
- Generating test cases. The collection of scenarios for a use case may suggest a suite of test cases for those scenarios.