A use case is a list of actions or event steps define the interactions between a role and a system to achieve a goal. The actor can be a human or other external system. Use case diagram have only 4 major elements:
- The actors that the system you are describing with interacts with,
- The system rectangular box
- The use cases or service
- The lines that represent relationships between these elements.
- Relationship between actor and use case;
An actor must be related with at least one use case or multiple use cases. Or multiple actors can be relationship with single use case.
- Generalization of an actor;
In use case, the actor generalization refers to the relationship which can exist between two actors and which shows that one actor receive the role and properties of another actor.
- Generalisation of a use case;
In the use case, the use case generalization refers to the relationship which can exist between two use cases and which shows that one use case as refer child receive the structure, behaviour, and relationships of another actor which is known as parent.
Parent class doesn’t exist without none of child classes.
- Extend between two use cases;
Parent class exist without child class.
- Include between two use cases;
Parent class is not complete without child classes.