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UT Dallas CS 6359 - Chapters_6b

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Slide 1What will we learn?Use CasesSlide 4How to Find Use CasesDefining Use Cases: System BoundariesUse Cases: Identify Primary Actors and GoalsUse Cases: Identify Actors, GoalsUse Cases: Primary Actors and System BoundariesPOS Case Study: Primary ActorUse Cases: Putting it all TogetherUse Cases: How Big or Small?Applying UML: Use Case DiagramsExample: POSUML Use Case DiagrammingUML Use Case Diagramming (alt)Use Cases – Some ObservationsCase Two: The Monopoly GameMonopoly Game Use CaseMonopoly Game: Use Case DiagramMonopoly Game Use CaseMonopoly Game Use CaseUse Cases and Iterative MethodsRequirements WorkshopsIterative Development: Disciplines, Phases, and ArtifactsIterative Development: Disciplines, Phases, and ArtifactsIterative Development: Disciplines, Phases, and ArtifactsTakeaways from Chapters 6Next …Object-Oriented Analysis and DesignCHAPTER 6: USE CASES, PART II1What will we learn?How to define use cases, how to find them, how to construct themApplying UML use case diagramsHow to work with use cases in iterative methodsRelating use cases2Use CasesUse cases are text, not diagramsWe may construct diagrams from the text cases laterThese are created as stories, and functional requirements are derived from themActors: something that exhibits behavior in the system (not just a person)Scenario: A specific sequence of actions and interactions between the actors and the system (use case instance)One particular story of using the systemUse Case (informal): A collection of related success and failure scenarios that describe an actor using a system to achieve a goal.Use Case (formal, RUP): A set of use-case instances (scenarios), where each instance is a sequence of actions a system performs that yields an observable result of value to a particular actor. 3O p e r a tio n : e n te rIte m ( … )P o s t-c o n d itio n s :- . . .O p e r a t io n C o n t r a c t sS a led a te. . .S a le sL in e It e mq u a n tity1 ..*1. . .. . .D o m a i n M o d e lU s e - C a s e M o d e lD e s i g n M o d e l: R e g is t e re n te r I t e m(it e m ID , q u a n t it y ): P r o d u c t C a t a lo gs p e c = g e t P r o d u c tS p e c ( ite m ID )a d d L in e Ite m ( s p e c , q u a n t it y ): S a leo b je c ts , a t tr ib u te s , a s s o c ia tio n sR e q u ir e -m e n tsB u s in e s s M o d e l i n gD e s i g nS a m p le U P A r t i f a c t R e l a t i o n s h i p s: S y s t e me n te r I t e m( id , q u a n t ity )U s e C a s e T e x tS y s t e m S e q u e n c e D ia g r a m sm a k eN e w S a le ( )s y s te m e v e n t sC a s h ie rP ro c e s s S a le: C a s h ie ru s e c a s e n a m e ss y s te m o p e r a t io n sU s e C a s e D ia g r a mV is io nS u p p le m e n ta r yS p e c ifi c a tio nG lo s s a rys c o p e , g o a ls , a c t o r s , fe a t u r e ste r m s , a t tr ib u t e s , v a lid a tio nn o n - fu n c t io n a l r e q s , q u a lity a t tr ib u t e sr e q u ire m e n t sP ro c e s s S a le1 . C u s to m e r a r r iv e s ...2 . C a s h ie r m a k e s n e w s a le .3 . ...4How to Find Use CasesOne the hardest, but most important parts of the projectsAll understanding of the requirements, and hence system design, will flow from hereInteract closely with customer/client/userHere customer means the person purchasing the softwareOne great strategy – take an actor perspective, role playEach use case should be designed to satisfy a goal or a primary actor5Defining Use Cases: System BoundariesChoose a System BoundaryDetermine the edges of the system being designed – is it the software, the software and hardware? Does it include the person using the system?We are determining the Domain for the systemThink about our POS Case Study … what is the system boundary?In this case, the system under design is the software and hardware associated with itThe cashier, store databases, payment authorization services, etc. are outside the boundary of the systemNote that does not mean that they are not important – they are simply outside the boundaryHaving trouble identifying the boundary? Identify the external actors, and that should help define it6Use Cases: Identify Primary Actors and GoalsActors and goals are usually defined together, because in order to identify the primary actor, you usually must know what his/her goal isAsk the fundamental questions: How is the system being used, and by whom?Who starts the action, who provides what, who monitors, etc.Remember, actors can be other systems, like a payment system or a database – not necessarily human users! This is usually done in the requirements workshop brainstorm sessions One useful approach: create a table, list all actors and goals, and then identify the primariesRemember, the primary actor is the one that has a need or goal fulfilled by the systemSecondary (supporting) actors provide a service to the systemOffstage actors have an interest in the behavior of the system, but are not primary or supportingNote the primary actor may be defined based upon the choice of system boundary7Use Cases: Identify Actors, GoalsIn Use Case Modeling, in order identify the actors and their goals, we need to understand the system from the actors’ perspectivesWho is using the system? What are they doing with the system?Best approach to this is to identify the actors and then ask “What are your goals? Are they measurable?”This gets to the heart of what the stakeholders really want from the systemAlso helps to avoid slipping into design too early – if we concentrate on the end goals, everyone stays open to new solutions to meet those goals8Use Cases: Primary Actors and System BoundariesGoal: Process salesCashierCustomerPOS SystemCheckout ServiceGoal: …


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UT Dallas CS 6359 - Chapters_6b

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