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UML Diagrams
Zicomi Systems publishes some UML example diagrams online from the world famous UML dictionary.
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Version 2.5 Released
Zicomi Systems is delighted to announce that version 2.5 of Zicomi Mentor is released. With support for UML 2.0 and all thirteen UML diagrams
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Zicomi Systems' Director
speaks about the UML at Objects by Design - an informative interview
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Partner Programme
Zicom Systems is delighted to announce a new world wide partner programme, become a partner today.
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OMG Member
Zicom Systems is made a member of the OMG!
Use Case
Use Case  
A use case represents the behavior of the entity, describing the interaction between the actors and the use case in a series of actions, with possible variants. It describes the value the entity provides to the actor with which it communicates. The use case never describes "how" the value is achieved, just "what" the value is.

This is alternative content.

Explanation

A use case describes an interaction between the actors and the entity (most commonly a system) that is modeled. They always describe an observable piece of value as seen from the actor's point of view. As with all UML elements "behind" the graphical representation is a descriptor. In the case of the use case this descriptor forms the larger part of the definition of the use case. This descriptor describes the exchange of messages between the actor and the entity; what the entity does to provide the value to the actor, and the possible variants from the usual exchange, including errors, exceptional behavior and conditional behavior.

Important Points

A use case describes the "what" the entity does but never the "how" it is done. The use case is a behavioral element and as such it describes the behavior that the entity exhibits not the way that behavior is achieved by the entity.
Use cases are always written from the view point of the actor. The use case describes the value that the system provides to an actor, and is written from the actor's point of view. It describes the messages or interaction between the actor and the system describing what the system does to provide the value to the actor.
Use cases are separate behavioral elements. A use case defines behavior that is not impacted upon by the behavior in another use case. When an instance of a use case is executing it cannot be interrupted by any events or actions that result from the execution of another use case. In this way it is said to be performing an atomic transaction, that is one that cannot be interrupted.

Related Entries

Extension Point
Extension Point  Owned Element
An extension point is related to a use case because it is an owned element of a use case. It appears in a separate compartment and defines point in the use case where the behavior of the use case is extended. The extending behavior is defined in another use case which is related to the extended use case by an extend relationship.
Collaboration
Collaboration  Graphically Similar,  Used Together
A collaboration is related to a use case in the sense that they are drawn with the same fundamental shape - the ellipse. The perimeter of the collaboration being dotted. The collaboration can be used with any classifier, but when used with the use case it describes the realization of the use case. The interactions defined within the collaboration describe how instances of the use case provide the value described in the use case.
Actor
Actor  Used Together
An actor is related to a use case or a group of use cases by virtue of the fact that the entity provides some observable value to the actor and this value is described in the use case.

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