A use case diagram is a visual representation that depicts the interactions between external actors and the functionalities (or “use cases”) of a system. It is a part of the Unified Modeling Language (UML), which is a standardized method to visualize the design of a system. Use case diagrams help in understanding the requirements of a system, and they are used during the requirements elicitation phase of software development.
Components of a Use Case Diagram:
- Actor: This is an external entity that interacts with the system. It could be a user, another system, or any entity that needs to interact with the given system. In diagrams, it’s typically depicted as a stick figure.
- Use Case: Represents a specific functionality or action provided by the system. It is typically illustrated as an ellipse.
- System Boundary: This is usually represented as a rectangle that encompasses the use cases. It shows the boundary of the system being modeled, indicating the scope of the system.
- Relationships:
- Association: A simple line connecting an actor to a use case. It shows that an actor interacts with a particular use case.
- Include: This is a directed relationship between two use cases. It indicates that the behavior of one use case (the base) is augmented by another use case.
- Extend: Another directed relationship where one use case conditionally adds the behaviors of another.
- Generalization: Represents inheritance between actors or between use cases.
For instance, consider a simple use case diagram for an online book store:
- Actors: Customer, Admin
- Use Cases: Browse Books, Purchase Book, Add New Book, Update Book Info, Remove Book
In the diagram:
- The Customer actor might be associated with “Browse Books” and “Purchase Book” use cases.
- The Admin actor might be associated with “Add New Book”, “Update Book Info”, and “Remove Book” use cases.
- Relationships will be drawn as lines connecting actors to their respective use cases.
This use case diagram would provide a high-level understanding of the main functionalities of the online book store and the roles and interactions of different users. It sets a foundation for deeper analysis and detailed design in subsequent phases of software development.
