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DesignPatterns,ArchitecturalPatternsPascalMolliUniversityHenri-PoincaréPascal.Molli@loria.fr1Bibliography…?
ASystemofPattern
?BushmannetAll?
DesignPatterns
?GammaetAll?
ConcurrentProgramminginJava
?D.Lea.?
DistributedObjects
?OrfalietAll?
ApplyingUMLandPatterns
?Larman2Patterns…?
Patternshelpyoubuildonthecollectiveexperienceofskilledsoftwareengineers.
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Theycaptureexisting,well-provenexperienceinsoftwaredevelopmentandhelptopromotegooddesignpractice
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Everypatterndealswithaspecific,recurringprobleminthedesignorimplementationofasoftwaresystem
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Patternscanbeusedtoconstructsoftwarearchitectureswithspecificproperties…
?3BecomingaChessMasterFirstlearnrulesandphysicalrequirementse.g.,namesofpieces,legalmovements,chessboardgeometryandorientation,etc.
Thenlearnprinciplese.g.,relativevalueofcertainpieces,strategicvalueofcentersquares,powerofathreat,etc.
However,tobecomeamasterofchess,onemuststudythegamesofothermastersThesegamescontainpatternsthatmustbeunderstood,memorized,andappliedrepeatedlyTherearehundredsofthesepatterns4BecomingaSoftwareDesignerMasterFirstlearntherulese.g.,thealgorithms,datastructuresandlanguagesofsoftware
Thenlearntheprinciplese.g.,structuredprogramming,modularprogramming,objectorientedprogramming,genericprogramming,etc.
However,totrulymastersoftwaredesign,onemuststudythedesignsofothermastersThesedesignscontainpatternsmustbeunderstood,memorized,andappliedrepeatedlyTherearehundredsofthesepatterns5SoftwareArchitectureAsoftwarearchitectureisadescriptionofthesubsystemsandcomponentsofasoftwaresystemandtherelationshipsbetweenthem.
Subsystemsandcomponentsaretypicallyspecifiedindifferentviewstoshowtherelevantfunctionalandnon-functionalpropertiesofasoftwaresystem.
Thesoftwaresystemisanartifact.Itistheresultofthesoftwaredesignactivity.6ComponentAcomponentisanencapsulatedpartofasoftwaresystem.Acomponenthasaninterface.Componentsserveasthebuildingblocksforthestructureofasystem.
Ataprogramming-languagelevel,componentsmayberepresentedasmodules,classes,objectsorasetrelatedfunctions.7SubsystemsAsubsystemisasetofcollaboratingcomponentsperformingagiventask.Asubsystemisconsideredaseparateentitywithinasoftwarearchitecture.
Itperformsitsdesignatedtaskbyinteractingwithothersubsystemsandcomponents…8ArchitecturalPatterns AnarchitecturalPatternexpressafundamentalstructuralorganizationschemaforsoftwaresystems.Itprovidesasetofpredefinedsubsystems,theirresponsibilities,andincludesrulesandguidelinesfororganizingtherelationshipsbetweenthem.9Designpatterns Adesignpatternprovidesaschemeforrefiningthesubsystemsorcomponentsofasoftwaresystem,ortherelationshipsbetweenthem.Itdescribesacommonly-recurringstructureofcommunicatingcomponentsthatsolvesageneraldesignproblemwithinaparticularcontext.10Idioms AnIdiomisalow-levelpatternspecifictoaprogramminglanguage.Anidiomdescribeshowtoimplementparticularaspectsofcomponentsortherelationshipsbetweenthemusingthefeaturesofthegivenlanguage.11Framework Aframeworkisapartiallycompletesoftware(sub-)systemthatisintendedtobeinstantiated.Itdefinesthearchitectureforafamilyof(sub-)systemsandprovidesthebasicbuildingblockstocreatethem.Italsodefinestheplaceswhereadaptationsforspecificfunctionalityshouldbemade.12FirstExampleADiceGameAPlayerrolls10x2dicesIfresult=7,score=score+10pointsAttheend,scoreoftheplayerisregistredinthehighscoretable.13menuviewHighscoreStartturn=0RollDiceturn++UpdatehighscoreTurn<10[highscore][start][exit][true][false]ActivityDiagram14AnalysisDiagram…15DesignStageManageUserInterfaceManagePersistenceofhighscoreinafileorinrelationaldatabaseRealizeanlayeredarchitecture:ApplytheLayerArchitecturalPattern16Layerhelpstostructureapplicationthatcanbedecomposedintogroupsofsubtasksinwhicheachgroupofsubtasksisataparticularlevelofabstraction.17Layer:examples18Layer:Structure19Layer:Structure20Layerandcomponents…21Layers:VariantsRelaxedLayeredSystem:Alayer?
j
?canuseserviceofj-1,j-2…AlayercanbepartiallyopaqueSomeservicetolayerj+1,otherstoallupperservices…Layeringthroughinheritance:LowerlayersareimplementedasbaseclassesHigherlevelcanoverridelowerlevel…22Layers:KnownUsesVirtualmachines:JVMandbinarycodeformatAPI:LayerthatencapsulateslowerlayersInformationSystemPresentation,Applicationlogic,DomainLayer,DatabaseWindowsNT(relaxedfor:kernelandIOandhardware)Systemservices,Resourcemanagement(Objectmanager,securitymonitor,processmanager,I/Omanager,VMmanager,LPC),Kernel(exceptionhandling,interrupt,multiprosynchro,threads),HAL(HardwareAbstractionLevel)Hardware23Layers:benefitsReuseoflayersSupportforstandardization(POSIX)DependenciesarekeptlocalExchangeabilities:ReplacementofoldimplementationwithAdapterPatternDynamicexchangewithBridgePattern24Layers:LiabilitiesCascadesofchangingbehaviorLowerefficiencyUnnecessarywork:functionsofalayercalledmanytimesforoneserviceDifficultyofestablishingcorrectgranularityoflayers:Tofewlayer->lessbenefits,tomuchlayer->complexityandoverhead…25ApplyingLayerArchitecturePlayViewHighScoreFichierouBDDUICorePersistence26Package
decompositionUI<<layer>>Core<<layer>>Persist<<layer>>Util<<subsystem>>27Layer?
core
?Containbusinesslogicclasses…AdaptanalysisclassesforimplementationUseofsingletonIdiom…28Singleton(Idiom)Ensureaclassonlyhasoneinstance,andprovideaglobalpointofaccesstoit.29SingletonStructure30Core?
Layer
?:1erdiagrammeDesignAnalyse31Package
decompositionUI<<layer>>Core<<layer>>Persist<<layer>>Util<<subsystem>>32ObserverOne-to-manydependencybetweenobjects:changeofoneobjectwillautomaticallynotifyobservers33Observer:ApplicabilityAchangetooneobjectrequireschanginganunknownsetofothersObjectshouldbeabletonotifyothersthatmaynotbeknownatthebeginning34Observer:Structure35Observer:ConsequencesAbstractcouplingbetweensubjectandobserverSupportforbroadcastcommunicationHardtomaintain36ApplyingObserverPattern37ObserverView38Viewsaregraphicalobjects39SettingupObserver40Observer:ChangePropagation:Die:Randomizer:DieView1:getValue()2:setValue(int)3:notifyObservers()4:update(Observable,Object)5:getState()3:JLabel6:setText(3)41Architectureencouche...UICoreDecouplingclassesandinterfaces42Package
decompositionUI<<layer>>Core<<layer>>Persist<<layer>>Util<<subsystem>>43PatternFactoryMethodIntentDefineaninterfaceforcreatinganobject,butletsub-classesdecidewhichclasstoinstantiateletaclassdeferinstantiationtosubclassesAlsoknownasVirtualConstructor44FactoryMethod Applicability:Usewhenaclasscannotanticipatetheclassofobjectsitmustcreateaclasswantsitssubclassestospecifytheobjectsitcreatesclassesdelegateresponsibilitytooneofseveralhelpersubclasses,andyouwanttolocalizetheknowledgeofwhichhelpersubclasstodelegate.45Structure46FactorymethodConsequencesProvidehooksforsubclassesconnectsparallelclasshierarchiesKnownusesMacApp,ET++ClassViewinsmalltalk80MVC(controllercreation)OrbixORBforgeneratingPROXYobject47Layer?
Persist
?ClassestechniquesdepersistancesAssurerl
’indépendanceCore/Persistpouvoirchangerde?
persistentengine
?Parexemple:Persistancepar?
Sérialisation
?Persistanceviaunebasededonnéesrelationnelle(JDBC).48ApplyingFactoryProduitabstraitFabriqueabstraiteProduitconcretFabriqueconcrête49ApplyingFactory50Summary1Architecturalpattern:Layer2DesignPatterns:Observer,Factory1Idiom:SingletonPb:Combiningpatterntocombinetheirforces…5152
Bankexample…Abasicbanksystem:1bank,nAccount.
Eachaccountbelongto1client.Eachaccountiscreditedbyanamountamoney.BankfunctionsWithdrawalonaaccount,Creditanaccount,Transfermoneyfromoneaccounttoanother…53Naivesolution54NaiveSolution55ApplyingCommandPattern…Encapsulatearequestasanobject,therebylettingyouparameterizeclientswithdifferentrequests,queueorlogrequests,andsupportundoableoperations.56CommandExample57CommandExample58CommandStructure59CommandStructure60CommandConsequencesCommanddecouplestheobjectthatinvokestheoperationfromtheonethatknowshowtoperformit.Commandsarefirst-classobjects.Theycanbemanipulatedandextendedlikeanyotherobject.
It'seasytoaddnewCommands,becauseyoudon'thavetochangeexistingclasses.61ApplyingCommandPattern62ApplyingCommandPattern63CompositePatternComposeobjectsintotreestructurestorepresentpart-wholehierarchies.Compositeletsclientstreatindividualobjectsandcompositionsofobjectsuniformly.64CompositeExample65CompositeExample66CompositeStructure67ApplyingCompositeonCommand68ApplyingComposite6970ApplyingSingleton71AndSoon…Storingstate:MementoPatternObservingAccount:ObserverPatternVisitingallobjectgraph:VisitorPatternRemoteaccess:Proxypattern…72ProxyPatternProvideasurrogateorplaceholderforanotherobjecttocontrolaccesstoit.73ProxyExample74ProxyStructure75Proxybenefitsremoteproxycanhidethefactthatanobjectresidesinadifferentaddressspace.Avirtualproxycanperformoptimizationssuchascreatinganobjectondemand.
Bothprotectionproxiesandsmartreferencesallowadditionalhousekeepingtaskswhenanobjectisaccessed.76From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al77AdapterPatternConverttheinterfaceofaclassintoanotherinterfaceclientsexpect.Adapterletsclassesworktogetherthatcouldn'totherwisebecauseofincompatibleinterfaces.78AdapterExample79AdapterStructure80VisitorPatternRepresentanoperationtobeperformedontheelementsofanobjectstructure.Visitorletsyoudefineanewoperationwithoutchangingtheclassesoftheelementsonwhichitoperates.81Visitorexample82Visitorexample83Visitorapplicabilitymanydistinctandunrelatedoperationsneedtobeperformedonobjectsinanobjectstructure,andyouwanttoavoid"polluting"theirclasseswiththeseoperations84VisitorStructure85VisitorStructure86VisitorConsequencesVisitormakesaddingnewoperationseasyAvisitorgathersrelatedoperationsandseparatesunrelatedonesAddingnewConcreteElementclassesishardVisitingacrossclasshierarchiesAccumulatingstate.Breakingencapsulation87ChainofresponsabilityAvoidcouplingthesenderofarequesttoitsreceiverbygivingmorethanoneobjectachancetohandletherequest.Chainthereceivingobjectsandpasstherequestalongthechainuntilanobjecthandlesit.88
89ChainofResponsability90Chainofresponsability91ParticipantsHandler(HelpHandler) definesaninterfaceforhandlingrequests.(optional)implementsthesuccessorlink.ConcreteHandler(PrintButton,PrintDialog)handlesrequestsitisresponsiblefor.canaccessitssuccessor.iftheConcreteHandlercanhandletherequest,itdoesso;otherwiseitforwardstherequesttoitssuccessor.Client
initiatestherequesttoaConcreteHandlerobjectonthechain.92Example…Awt1.0From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al93StrategyDefineafamilyofalgorithms,encapsulateeachone,andmaketheminterchangeable.Strategyletsthealgorithmvaryindependentlyfromclientsthatuseit.94Strategy…95Strategy96ParticipantsStrategy(Compositor)declaresaninterfacecommontoallsupportedalgorithms.ContextusesthisinterfacetocallthealgorithmdefinedbyaConcreteStrategy.ConcreteStrategy(SimpleCompositor,TeXCompositor,ArrayCompositor)implementsthealgorithmusingtheStrategyinterface.Context(Composition)isconfiguredwithaConcreteStrategyobject.maintainsareferencetoaStrategyobject.maydefineaninterfacethatletsStrategyaccessitsdata.97Strategy…From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al98StateAllowanobjecttoalteritsbehaviorwhenitsinternalstatechanges.Theobjectwillappeartochangeitsclass.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al99ExempleFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al100StructureFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al101ConsequencesItlocalizesstate-specificbehaviorandpartitionsbehaviorfordifferentstatesItmakesstatetransitionsexplicitStateobjectscanbesharedFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al102DecoratorAttachadditionalresponsibilitiestoanobjectdynamically.Decoratorsprovideaflexiblealternativetosubclassingforextendingfunctionality.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al103ExampleFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al104ExampleFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al105ExampleFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al106StructureFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al107Applicabilitytoaddresponsibilitiestoindividualobjectsdynamicallyandtransparently,thatis,withoutaffectingotherobjects.forresponsibilitiesthatcanbewithdrawnwhenextensionbysubclassingisimpracticalFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al108ConsequencesMoreflexibilitythanstaticinheritanceAvoidsfeature-ladenclasseshighupinthehierarchyAdecoratoranditscomponentaren'tidenticalLotsoflittleobjectsFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al109From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al110BridgeDecoupleanabstractionfromitsimplementationsothatthetwocanvaryindependently.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al111BridgeFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al112BridgeFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al113BridgeStructure…From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al114BridgeDecouplinginterfaceandimplementationImprovedextensibilityHidingimplementationdetailsfromclientsFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al115ExampleFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al116From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al117BuilderSeparatetheconstructionofacomplexobjectfromitsrepresentationsothatthesameconstructionprocesscancreatedifferentrepresentations.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al118BuilderFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al119BuilderStructure…From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al120BuilderFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al121BuilderConsequencesItletsyouvaryaproduct'sinternalrepresentationItisolatescodeforconstructionandrepresentationItgivesyoufinercontrolovertheconstructionprocessFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al122FlyWeightUsesharingtosupportlargenumbersoffine-grainedobjectsefficiently.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al123FlyWeightFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al124Flyweight:StructureFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al125FlyweightexampleFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al126Flyweight:InstancesFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al127Flyweight:ApplicabilitéEtatintrinsèque/extrinsèque…Lesétatsextrinsèquespeuventêtrecalculés…From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al128Flyweight(ilariencompris…)From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al129IteratorProvideawaytoaccesstheelementsofanaggregateobjectsequentiallywithoutexposingitsunderlyingrepresentationFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al130IteratorFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al131Iteratorexample:From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al132ExempleFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al133MementoWithoutviolatingencapsulation,captureandexternalizeanobject'sinternalstatesothattheobjectcanberestoredtothisstatelater.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al134MementoStructure…From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al135Memento…PreservingencapsulationboundariesItsimplifiesOriginatorUsingmementosmightbeexpensive.DefiningnarrowandwideinterfacesHiddencostsincaringformementosFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al136CaseStudyFrom?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al137Designproblems…Documentstructure.ThechoiceofinternalrepresentationforthedocumentaffectsnearlyeveryaspectofLexi'sdesign.Allediting,formatting,displaying,andtextualanalysiswillrequiretraversingtherepresentation.Thewayweorganizethisinformationwillimpactthedesignoftherestoftheapplication.
Formatting.HowdoesLexiactuallyarrangetextandgraphicsintolinesandcolumns?Whatobjectsareresponsibleforcarryingoutdifferentformattingpolicies?Howdothesepoliciesinteractwiththedocument'sinternalrepresentation?
From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al138Designproblems…Embellishingtheuserinterface.Lexi'suserinterfaceincludesscrollbars,borders,anddropshadowsthatembellishtheWYSIWYGdocumentinterface.SuchembellishmentsarelikelytochangeasLexi'suserinterfaceevolves.Henceit'simportanttobeabletoaddandremoveembellishmentseasilywithoutaffectingtherestoftheapplication.
Supportingmultiplelook-and-feelstandards.Lexishouldadapteasilytodifferentlook-and-feelstandardssuchasMotifandPresentationManager(PM)withoutmajormodification.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al139Designproblems…Embellishingtheuserinterface.Lexi'suserinterfaceincludesscrollbars,borders,anddropshadowsthatembellishtheWYSIWYGdocumentinterface.SuchembellishmentsarelikelytochangeasLexi'suserinterfaceevolves.Henceit'simportanttobeabletoaddandremoveembellishmentseasilywithoutaffectingtherestoftheapplication.
Supportingmultiplelook-and-feelstandards.Lexishouldadapteasilytodifferentlook-and-feelstandardssuchasMotifandPresentationManager(PM)withoutmajormodification.From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al140Designproblems…Spellingcheckingandhyphenation.HowdoesLexisupportanalyticaloperationssuchascheckingformisspelledwordsanddetermininghyphenationpoints?Howcanweminimizethenumberofclasseswehavetomodifytoaddanewanalyticaloperation?From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al141From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al142From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al143From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al144From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al145From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al146From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al147From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al148From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al149From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al150From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al151From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al152From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al153From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al154From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al155From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al156From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al157Summary(C.Alexander)Itispossibletomakebuildingbystringingtogetherpatterns,inaratherlooseway.Abuildingmadelikethis,isanassemblyofpatterns.Itisnotdense.Itisnotprofound.Butitisalsopossibletoputpatternstogetherinsuchwaythatmanypatternsoverlapinthesamephysicalspace:thebuildingisverydense;ithasmanymeaningscapturedinasmallspace;andthroughthisdensity,itbecomesprofound.158ArchitecturalPatterns…FromMUDtoStructure…Layers,PipeandFilters,BlackboardDistributedSystems…Broker,PipeandFilters,MicrokernelInteractiveSystems…MVC,PACAdaptableSystems…Microkernel,Reflection…159Layerhelpstostructureapplicationthatcanbedecomposedintogroupsofsubtasksinwhicheachgroupofsubtasksisataparticularlevelofabstraction.160Layer:examples161Layer:Structure162Layer:Structure163Layerandcomponents…164LayerandFacadeDP…165LayerandFacadeDP166Layers:VariantsRelaxedLayeredSystem:Alayer?
j
?canuseserviceofj-1,j-2…AlayercanbepartiallyopaqueSomeservicetolayerj+1,otherstoallupperservices…Layeringthroughinheritance:LowerlayersareimplementedasbaseclassesHigherlevelcanoverridelowerlevel…167Layers:KnownUsesVirtualmachines:JVMandbinarycodeformatAPI:LayerthatencapsulateslowerlayersInformationSystemPresentation,Applicationlogic,DomainLayer,DatabaseWindowsNT(relaxedfor:kernelandIOandhardware)Systemservices,Resourcemanagement(Objectmanager,securitymonitor,processmanager,I/Omanager,VMmanager,LPC),Kernel(exceptionhandling,interrupt,multiprosynchro,threads),HAL(HardwareAbstractionLevel)Hardware168Layers:benefitsReuseoflayersSupportforstandardization(POSIX)DependenciesarekeptlocalExchangeabilities:ReplacementofoldimplementationwithAdapterPatternDynamicexchangewithBridgePattern169Layers:LiabilitiesCascadesofchangingbehaviorLowerefficiencyUnnecessarywork:functionsofalayercalledmanytimesforoneserviceDifficultyofestablishingcorrectgranularityoflayers:Tofewlayer->lessbenefits,tomuchlayer->complexityandoverhead…170PipesandFiltersProvidesastructureforsystemsthatprocessastreamofData.Eachprocessingstepisencapsulatedinafiltercomponent.Dataispassedthroughpipesbetweenadjacentfilters.Recombiningfiltersallowstobuildfamiliesofrelatedsystems.171PipesandFilters:Example172PipesandFilters:Structure173PipesandFilters174PipesandFilters:pushpipeline175PipesandFilters:pullpipeline176PipesandFilters:push-pullpipeline177PipesandFilters:ThreadedFilters178PipesandFilters:KnownUsesUnixCMSPipelines(extensionIBMmainframes)LASSPTools(NumericalAnalysis)Graphicalinputdevices(knobsorsliders)FiltersfornumericalanalysisanddataextractionDatasinkstoproduceanimationfromnumericaldatastreams…Khoros:Imagerecognition…WEB!!Servlet!!179PipesandFiltersbenefitsNointermediatefilenecessary(butpossible)FlexibilitybyfilterexchangeFlexibilitybyrecombinationReuseoffiltercomponentsRapidprototypingofpipelineEfficiencybyparallelprocessing180PipesandFiltersLiabilitiesSharingstateinformationisexpensiveorinflexibleEfficiencygainbyparallelprocessingisoftenanillusion
Costofdatatransfer,filtersthatconsumealldatabeforeoneoutput,contextswitchononecomputer,synchronizationoffiltersviapipesDatatransformationoverheadErrorHandling181[SunDeveloppers]From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al182From?
SystemofPatterns
?Buschmann&Alland?
DesignPattern
?Gamma&Al183Blackboard TheBlackboardarchitecturalpatternisusefulforproblemsforwhichnodeterministicsolutionstrategiesareknown.Severalspecializedsubsystemsassembletheirknowledgetobuildapossiblypartialorapproximatesolution.184BlackboardExample185BlackboardStructure186BlackboardStructure187BlackboardStructure188BlackboardVariantsProductionSystem(OPSLanguage)Blackboard:workingmemoryKnowledgesource:Condition-actionrulesControl:conflictresolutionmodule.
Repository:
blackboard:Data,
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