Use case model gives a static view of the system functions and their static relationships both with external entities and with one another.
It is a functional model which provide description of a system’s behaviour from users standpoint by answering the following questions.
- What functions does the system offer?
- What external agents interact with the system?
- In what functions are those external agents involved?
Use case diagrams illustrate the relationship between actors and use cases
Use Case model is very useful for capturing the functional requirements.