View source for OCUP2F 05 Use Case Diagram

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[[Category:OCUP2]]
==Module 3. Use Case Diagram⌘==
===Use Case Diagram⌘===
[[File:OCUPUseCaseDiagram.png]]
====Use Case Diagram key concepts⌘====
* '''Use cases''' are used to model the '''requirements''' of a system (what a system is supposed to do)
* The key concepts associated with use cases are '''actors''', '''use cases''', and the '''subject'''.
* UCD describes the relationships among a set of use cases and the actors participating in these use cases
* it does NOT describe behavior or flows ('''WHO''' and '''WHAT''', not '''HOW''')

===Actor⌘===
[[File:OCUPActor.png]]
* a '''role''' played by an '''external entity''' - a user or any other system that interacts with the subject
* may represent roles played by human users, external hardware, or other subjects
* Notation: "stick man" icon (with the name above or below) or rectangle
===Relationships Between Actors⌘===
[[File:ActorRelationship.png]]
*Generalization
*Specialization

===UseCase⌘===
[[File:OCUPUseCase.png]]
* the specification of a set of actions performed by a system and produce a '''result'''
* a '''complete''' set of actions that perform a function for a particular actor
* Notation: an ellipse (with the name inside or below) or rectangle with stereotype

===Subject⌘===
[[File:UseCaseSubject.png]]
* a system (subject) is a box containing use cases
* defines boundaries and responsibilities
* actors are '''always external''' to a system
* the subject rectangle '''does not''' imply that the subject classifier owns the contained Use Cases,

===Use Case ownership⌘===
[[File:ClipCapIt-150902-130342.PNG]]
* Notation for Use Case owned by Classifier

===Relationships Between Actors and Use Cases⌘===
[[File:UseCaseActorRelationship.png]]
*an '''association''' expresses a communication path between the actor and the use case
* '''directed association''' from the active to the passive element (who initiated the communication)
* association with '''multiplicity''' like 0..*, 2..*, *, etc
** '''at the actor end''' - more than one actor instance is involved in initiating the use case
** '''at the use case end''' - an actor can be involved in multiple use cases of that type
===Relationships Between Use Cases⌘===
Three types of relationship:
* «include»
* «extend»
* generalization / specialization
====Include⌘====
[[File:include-use-case.png]]
* defines that a use case contains the behavior defined in another use case
* behavior of the included use case is inserted into the behavior of the including use case
* included use case is '''not optional''', and is '''always required'''
=====Include - common part⌘=====
[[File:include-two-use-cases.png]]

* include relationship is intended to be used when there are '''common''' parts of the behavior of two or more use cases
* this common part is then extracted to a separate use case, to be included by all the base use cases having this part in common

=====Include Example⌘=====
[[File:OCUPInclude.png]]
* basic flow of events is '''incomplete''' without the inclusion

====Extend⌘====
[[File:OCUPExtend.png]]
* a relationship from an extending use case to an extended use case 
* specifies how and when the behavior defined in the extending use case can be inserted into the extended use case
* the extension takes place at '''extension point'''
* basic flow of events should still be '''complete'''

=====Extension Point⌘=====
[[File:ExtensionPointNotation.png]]

====Generalization⌘====
[[File:Generalization.png|385px]]
* the specific use case inherits the features of the more general use case
====Abstract Use Case⌘====
[[File:OCUPAbstractUseCase.png]]
* does not provide a complete declaration and can typically not be instantiated
* is intended to be used by other use cases, e.g., as a target of generalization relationship
* the name of an abstract Use Case is shown in ''italics''

===Use Case Diagram Example⌘===
[[File:UseCaseDiagramExampleWithNumbers.png]]

'''Questions'''
# Which use case could be abstract?
# Which actors are passive?
# Do dashed arrows (1, 2, 3) include or extend relationships?
# Which use case needs to have an extension point?

===Incorrect relationships examples⌘===
[[File:ClipCapIt-150902-150234.PNG]]
===Use Case relationship example⌘===
[[File:ClipCapIt-150902-125114.PNG]]
<!-- http://www.uml-diagrams.org/use-case-include.html -->

===Questions⌘===
* What is a difference between an actor and a user?

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