Use Case Diagram

Topic Outline

  • Use Case
  • Components of Use case
  • Actor
  • System Boundary
  • Relationship
  • Example

 Use Case Diagram

A use case is a pattern of behavior the system exhibit. Use cases are a sequence of actions that the user takes on the system to get the particular target. The use case is a dialogue between an actor and a system.

A use case model is a diagram or set of diagrams that together with some additional documentation show what the proposed software system is designed to do.

Components of Use Case

 
 

(1) Actor

An actor is someone or something that must interact with the system under development. Actors are not part of the system usually represented with a stick figure.

Shape 

An actor may be:

People, Computer hardware and devices, External systems

Primary Actor

  • Primary actors are completely outside the system. 
  • Acts on the system. 
  • Uses the system to fulfill his/her goal.

Secondary Actor

  • Secondary actors often appear to be more inside the system than outside.
  • Helps the system to fulfill its goal.

(2) System Boundary

It helps to identify what is external, internal and what the responsibilities of the system are. The external environment is represented only by actors. It is shown as a rectangle.

Shape 

(3) Relationship

The relationship is an association between the use case and the actor.

Use Case Relationship

  • External
  • Include
  • Generalization

External

The relationship is used to indicate that the use case completely consists of the behavior of another use case at once or at a specific point. It is shown as a dotted line with an arrow point and labeled <<external>>.

  

 

Include

This relationship inserts additional behavior into a base use case. It is shown as a dotted line with an open arrow and keyword <<include>>.


 

Generalization

The relationship between the child use case and the parent use case is the generalization relationship. It is shown as a solid line with a hollow arrow point.

Example:

ATM system can be used to pay bills. Pay bills have two child use cases. Pay credit card bills and pay utility bills.

ATM Banking System

Shape 

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