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Senin, 14 Oktober 2013

Use Case Diagram

A use case diagram is a graphic depiction of the interactions between system elements. A use case is a methodology used in system analysis to identify, clarify, and organize system requirements. In this context, the term system refers to something being developed or operated, such as a mail-order product sales and service Web site. Use case diagrams are employed in UML (Unified Modeling Language), a standard notation for the modeling of real-world objects and systems.


A use case diagram contains four components.
  •           The boundary, which defines the system of interest in relation to the world around it.
  •           The actors, usually individuals involved with the system defined according to their roles.
  •           The use cases, which are the specific roles played by the actors within and around the system.
  •           The relationships between and among the actors and the use cases.  



We can use the following elements in use case diagrams :

Actor : An actor represents a role that an outsider takes on when interacting with the business system. For instance, an actor can be a customer, a business partner, a supplier, or another business system.

Association : An association is the relationship between an actor and a business use case. It indicates that an actor can use a certain functionality of the business system - the business use case.

Use Case : A business use case describes the interaction between an actor and a business system, meaning it describes the functionality of the business system.

Include : The include relationship is a relationship between two business use cases that signifies that the business use case on the side to which the arrow points is included in the use case on the other side of the arrow. This means that for one functionality that the business system provides, another functionality of the business system is accessed.

Generalization : A generalization relationship is also a parent-child relationship between use cases. The child use case in the generalization relationship has the underlying business process meaning, but is an enhancement of the parent use case. In a use case diagram, generalization is shown as a directed arrow with a triangle arrowhead. The child use case is connected at the base of the arrow. The tip of the arrow is connected to the parent use case.

Extends : An extends shows the relationships between use cases. Relationship between use case A and use case B indicates that an instance of use case B may include (subject to specified in the extension) the behavior specified by A. An 'extends' relationship between use cases is depicted with a directed arrow having a dotted shaft. The tip of arrowhead points to the parent use case and the child use case is connected at the base of the arrow. For example, validating the user for a system. A invalid password is extension of validating password use case.




Here’s simple example of use case diagram about blog system :




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