A UML (Unified Modeling Language) use case diagram is a visual representation that depicts the interactions between users (or “actors”) and the functionalities (or “use cases”) of a system. It helps in understanding the requirements of a system and the roles of various actors interacting with it.
Here are the primary components of a UML use case diagram:
- Actor: An actor represents a user or any external system that interacts with the system being modeled. It’s usually drawn as a stick figure.
- Use Case: Represents a distinct function or action that the system provides. It’s usually drawn as an ellipse.
- System: The boundary of the system being modeled. It’s often represented as a rectangle encompassing the use cases, showing that these functionalities belong to the system.
- Relationships:
- Association: A simple line connecting an actor to a use case, indicating that the actor will interact with the system to achieve the use case.
- Include: Represents a scenario when one use case is included within another use case. This is typically used to capture a common function that occurs across multiple use cases.
- Extend: Denotes optional extensions to behavior. One use case can extend another, adding behaviors under specific conditions.
- Generalization: Represents inheritance, where one actor or use case inherits the properties of another.
Here’s a simple example to illustrate a use case diagram:
Imagine a library management system:
- Actors: Student, Librarian
- Use Cases: Borrow Book, Return Book, Check Overdue, Add New Book, Remove Book
In this scenario:
- Both the Student and Librarian can “Borrow Book” and “Return Book”.
- Only the Librarian has the ability to “Add New Book” or “Remove Book”.
- Both might want to “Check Overdue” books, but perhaps with different levels of detail.
In the use case diagram:
- The Student and Librarian actors would be represented as stick figures.
- The use cases would be ellipses containing the actions like “Borrow Book”, “Return Book”, etc.
- Associations (lines) would connect each actor to the respective use cases they can interact with.
This diagram would help developers, stakeholders, and project managers visualize and understand the primary functionalities of the library system and the roles and interactions of various users.
