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Lesson 3Review: use case diagram notation
ObjectiveReview the Modeling Elements of the Use Case Diagram.

Use case diagram notation

The first step in developing the use case model is the creation of a use case diagram.
The diagram consists of four fundamental model elements: the system, the actors, use cases, and associations.
  1. Actor: People, systems, and devices that have a stake in the successful operation of the system.
  2. System: Sets the context of the system in relation to the actors who use it and the features it must provide.
  3. Use case: Identifies the key features of the system. Without these features, the system will not fulfill the user/actor requirements. Each use case expresses a goal that the system must achieve.
  4. Association: Identifies an interaction between elements.

Use Case Diagram Notation
Not all tools implement the System icon because it is always the same, that is, a single rectangle for the system being described.
For all practical purposes, it is implied by the diagram itself.

Actors

Actors may be represented in the use case diagram with different icons for people, systems, and devices, or even subtypes of each of these three classifications The icons used to represent actors are not standard. The UML recommends, but does not dictate, the icons that represent model elements.

Associations

An association identifies a dialog between an actor and a use case or between use cases. An actor may initiate a dialog with a use case, as when a customer chooses the deposit function on an automated teller machine. The machine and customer continue the dialog until either an error condition occurs or the dialog is successfully completed. Focus your attention first on the associations between actors and use cases.
Alternatively, a use case may initiate the dialog in the form of a notification. The notification may or may not require a response from the user.
Dialogs are covered more extensively later in this module. For now, it is sufficient for you to know that some form of dialog is required in your model and to know who is involved.

Use Case Diagram Elements

Click the link below to match the correct model element labels to the visual elements of the use case diagram.
Use Case Diagram Elements