6/4/2015 UnderstandingUMLUseCasesModeling

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UnderstandingUseCaseModeling

SinanSiAlhir,http://sites.google.com/site/salhir/

Introduction

Following the "method wars" of the 1970s and 1980s, the Unified Modeling Language (UML)emerged from the unification that occurred in the 1990s within the information systems andtechnology industry. Unification was lead by Rational Software Corporation and Three Amigos,GradyBooch,JamesRumbaugh,andIvarJacobson.TheUMLgainedsignificant industrysupportfromvariousorganizationsvia theUMLPartnersConsortiumandwassubmitted toandadoptedbytheObjectManagementGroup(OMG)asastandard(November17,1997).

The UML is an evolutionary generalpurpose, broadly applicable, toolsupported, and industrystandardized modeling language for specifying, visualizing, constructing, and documenting theartifactsofasystemintensiveprocess.The language isbroadlyapplicable todifferent typesofsystems (software and nonsoftware), domains (business versus software), and methods andprocesses.TheUMLenablesandpromotes(butdoesnotrequirenormandate)ausecasedriven,architecturecentric, iterative, and incremental process that is object oriented and componentbased. The UML enables the capturing, communicating, and leveraging of knowledge: modelscapture knowledge (semantics), architectural views organize knowledge in accordance withguidelines expressing idioms of usage, and diagrams depict knowledge (syntax) forcommunication.

System development may be characterized as problem solving, including understanding orconceptualize and representing a problem, solving the problem by manipulating therepresentation of the problem to derive a representation of the desired solution, andimplementing or realizing and constructing the solution. This process is very natural and oftenoccurssubtlyandsometimesunconsciouslyinproblemsolving.

Modelsarecompleteabstractionsofsystems.Modelsareusedtocaptureknowledge(semantics)aboutproblemsandsolutions.Architecturalviewsareabstractionsofmodels.Architecturalviewsare used to organize knowledge in accordance with guidelines expressing idioms of usage.Diagrams are graphical projections of sets of model elements. Diagrams are used to depictknowledge(syntax)aboutproblemsandsolutions.WithinthefundamentalUMLnotation,conceptsare depicted as symbols and relationships among concepts are depicted as paths (lines)connectingsymbols.

Use casemodeling from the usermodel view (also known as the use case or scenario view),whichencompassesaproblemandsolutionasunderstoodbythoseindividualswhoseproblemthesolutionaddresses,involvesusecasediagramstodepictthefunctionalityofasystem.

UseCaseDiagrams

Tosuccessfullyapplyusecasediagrams,wemustfirstunderstandthetypesofelementsusedinusecasediagrams.

Actors

Actor classes are used tomodel and represent roles for "users" of a system, including humanusers and other systems. Actors are denoted as stick person icons. They have the followingcharacteristics:

Actorsareexternaltoasystem.Actorsinteractwiththesystem.Actorsmayusethefunctionalityprovidebythesystem,

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6/4/2015 UnderstandingUMLUseCasesModeling

http://www.methodsandtools.com/archive/archive.php?id=24 2/2

includingapplicationfunctionalityandmaintenancefunctionality.Actorsmayprovidefunctionalitytothesystem.Actorsmayreceiveinformationprovidedbythesystem.Actorsmayprovideinformationtothesystem.Actorclasseshaveactorsinstancesorobjectsthatrepresentspecificactors.

Figure 1 shows a project management system with a project manager actor and a projectdatabase actor. The projectmanager is a user who is responsible for ensuring the success ofproject and uses the system to manage projects. The project database is a system that isresponsibleforhousingprojectmanagementdata.

Figure1

UseCases

Usecaseclassesareusedtomodelandrepresentunitsoffunctionalityorservicesprovidedbyasystem(orpartsofasystem:subsystemsorclasses)tousers.Usecasesaredenotedasellipsesorovals.Theymaybeenclosedbyasystemboundaryorrectanglelabeledwiththenameofthecontainingsystem.Theyhavethefollowingcharacteristics:

Usecasesareinteractionsordialogsbetweenasystemandactors,includingthemessagesexchangedandtheactionsperformedbythesystem.Usecasesmayincludevariantsofthesesequences,includingalternativeandexceptionsequences.Usecasesareinitiatedbyactorsandmayinvolvetheparticipationofnumerousotheractors.Usecasesshouldprovidevaluetoatleastoneoftheparticipatingactors.Usecasesmayhaveextensionpointsthatdefinespecificpointswithinaninteractionatwhichotherusecasesmaybeinserted.Usecaseclasseshaveusecaseinstancesorobjectscalledscenariosthatrepresentspecificinteractions.Scenariosrepresentasingesequenceofmessagesandactions.

Figure 1 shows a project management system which provides the functionality to manageprojectsinwhichtheprojectmanagerandprojectdatabaseparticipate.

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