What is a Use Case Diagram?

A use case is a scenario by which a user case interacts with a system. A system can have multiple use cases. Use cases can be represented by use case diagram pictorially.

A UML use case diagram is a pictorial representation of use cases. In specific, it contains:

• Use cases of the system, shown as texts within ovals. These are written as verbs e.g. Place an order.
• The actors of the system. Actors are entities external to the system that trigger these use cases. Human users and other software systems may be actors. These are represented as stick figures. E.g. A cinema lover may be an actor who might trigger the above use case.
• Associations between use cases and actors, shown as straight lines connecting the two shapes.
• Optionally a rectangle showing the system boundary. Use cases rest within, and actors are outside.

You can find more use case examples in the pages below:

• Visual Paradigm Circle
• uml-diagrams.org

Useful UML Resources

• OMG UML Specification
• Popular UML modeling software
• UML tutorials