Introducing a Use Case Model

An actor initiates a use case, and an actor (possibly the initiator, but not necessarily) receives something of value from the use case.

Use Case model

note.GIF (411 bytes)An ellipse represents a use case, a stick figure represents an actor. The initiating actor is on the left of the use case, and the receiving actor is on the right. The actor's name appears just below the actor. The name of the use case appears either inside the ellipse or just below it. An association line connects an actor to the use case, and represents communication between the actor and the use case. The association line is solid, like the line that connects associated classes.

Each use case is a list of scenarios, and each scenario is a sequence of steps. Each scenario of each use case will also have its own page, listing in text from the:
Actor who initiates the use case
Preconditions for the use case
Steps in the scenario
Postconditions when the scenario is complete
Actor who benefits from the use case

Use case diagrams add more power to the requirements gathering. They visualize use cases, they facilitate communication between analysts and users and between analysts and clients. In a use case diagram, symbol for the use case is an ellipse, actor has a stick figure as a symbol, and association line joins an actor to a use case. The use cases are usually inside a rectangle that represents the system boundary.