A use case diagram organizes requirements by showing actors, the actions they trigger, and the logical boundary or context containing those actions. An actor may be a user or another subsystem. section 1.3 section 2.1.4
Because the diagram describes required functionality rather than implementation, it remains paradigm agnostic. It can support an agreement between developers and customers about what the program should do, regardless of the implementation stack. section 1.3 section 2.1.4
Use a use case diagram to:
- Identify which users or subsystems interact with a logical system boundary. section 2.1.4
- Capture the actions that each actor can perform with a subsystem. section 2.1.4
- Organize a traditional requirements model before choosing implementation techniques. section 1.3
Engine control
An astronaut acts as an actor who starts and stops an engine within the control subsystem. The diagram can expose the required operations without committing them to particular API calls or programming paradigms. section 1.3
Main menu
A main-menu diagram for Minecraft models the actions available to actors within that menu, providing a structured way to discuss functionality with a customer. section 2.1.4
Use case diagrams clarify functional scope, but they do not reveal a domain's functional properties well enough to guide functional declarative design directly. User scenarios can add concrete steps, alternative paths, and preconditions. section 2.1.4
