內容教程成果10.activity diagrams

ActivityDiagramsWhatareactivitydiagramsActionstatesTransitionsDecisionsForksandJoinsSwimlanesObjectflowsSignalsWhatareactivitydiagramsActivitydiagramsare“OOflowcharts”.Allowstomodelaprocessasacollectionofactivitiesandtransitionsbetweenthoseactivities.Anactivitydiagramcanbeattachedtoanymodelingelementtocapturethebehaviorofthatelement.Typically,itattachedto: 1).Usecase; 2).Classes 3).Interface; 4).Components; 5).Nodes; 6).Collaborations; 7).OperationsandmethodsWhatareactivitydiagrams(2)Agoodactivitydiagramisthatitisfocusedoncommunicatingonespecificaspectofasystemdynamicbehavior.Anactivitydiagramcontainstheminimumnecessaryamountofinformationtocommunicatethepoint.Wecanalsouseanactivitydiagramtomodelbusinessprocessandworkflows.Aguardisalogicalconditionthatwillreturnonly“true”or“false”.Aguardedtransitionoccursonlyiftheguardresolvesto“true”.ActionStatesActionstateisasimplifiedformofastatethathasasingleentryaction.Andtheyare: Atomic:can’tbebrokendownintosmallerpiecesUninterruptible:oncethepieceofworkstartsitalwaysprogressestofinishInstantaneous:theworkofanactionstateisgenerallyconsideredtotakeaninsignificantamountoftime.ActionstatesarerepresentedasrectanglewithroundedendsActionstatestateActionStates(2)Twoformsofactionexpression: 1).Pseudo-code:suchasi:=i+1 2).PlainEnglish:verborverbphraseEachactivitydiagramhastwospecialstates:- -thestartstate: -thestopstate:SubactivitystatesSubactivitystatesarenon-atomic,andhaveaspecialsyntax.Whenmodelingcomplexbusinessprocessesasaworkflow,youtendtousesubactivitystates.Subactivitystatescanbebrokendownintofinersubactivityandultimatelytoactionstates.TransitionsTransitionsindicatethemovementfromonestatetoanother.Example:WriteletterAddressletterPostletterStartstateStopstateActivitystatesDecisions-AdecisionspecifiesalternativepathsbasedonsomeBooleanguardexpression.Syntax:diamondshape.Abranchhasasingleingtransitionandseveralguardedoutgoingtransitions.Onlyoneoftheoutgoingtransitionscanbetaken,sotheguardsshouldbemutuallyexclusive.Using[else]asaguardindicatesthatthe“else”transitionshouldbeusedifallotherguardsonthebrancharefalse.Amergerhasmultipleinputtransitionsandasingleoutput.Amergermarkstheendofconditionalbehavior

ForksandjoinsUsingafork,cansplitapathintotwoormoreconcurrentflows,andsynchronizetheseconcurrentflowsusingajoin.Forkhasexactlyoneingtransitionandtwoormoreoutgoingtransitions.Joinhastwoormoreingtransitionandexactlyoneoutgoingtransition.Allofoutgoingtransitionsaretakeninparallel.JoinForkSwimlanesUMLdoesnotgiveanydetailedsemanticsforswimlane.Soyoucanpartitionactivitydiagramsinanywayyoulike.Swimlanesarecommonlyusedtorepresent:UsecaseClassesComponentsOrganizationalunitsRoles(inworkflowmodeling)ExampleObjectflowsActivitiesmayinputandoutputobjectsandcanmodifyobjectstate.Youcanshowthisonanactivitydiagramasanobjectflow.SignalsAsingleisatypeofevent,andawayofrepresentingapackageofinformationthatiscommunicatedasynchronouslybetweentwoobjects.Asignaleventoccurswhenanobjectreceivessignal.Asignalismodeledasaclasswiththestandardstereotype<<signal>>.Itonlyhasattributesandimplicitsend(targetSet)method.Asignalsendismodeledonanactivitydiagramasconvexpentagonlabeledwiththenameofsignalthatissent.Thereisnoactionassociatedwiththisstate,allitdoesissendthesignal.Drawadashedarrowfromthesignalsendtotheobjectthatreceivesthesignal.Asignalreceiptismodeledwithaconcavepentagonlabeledwiththenameofthesignalthatitreceived.Figure13.10WhentoUseactivityDiagramLikemostbehavioralmodelingtechniques,activitydiagramshavedefinitestrengthsandweakness,sotheyarebestusedincombinationwithothertechniques.Thegreatstrengthofactivitydiagramssupportsandencourageparallelbehavior.Thismakesthemagreattoolforworkflowmodelingformultithreadedprogramming.Theweaknessisactivitydiagramsdonotmakethelinksamongactionsandobjectsveryclear.Donot