软件工程（美国加州大学）

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1、ICS52IntroductiontoSoftwareEngineeringLectureNotesforSpringQuarter,2004AndrévanderHoekLecture5-1Copyright©2004,AndrévanderHoekDuplicationofcoursematerialforanycommercialpurposewithoutthewrittenpermissionofthelecturerisprohibited.©2004,UniversityofCalifornia,IrvineTod

2、ay’sLectureUSESrelationIS-COMPOSED-OFrelationCOMPRISESdiagramUSESdiagramInDesign,WeCanDoAnything…ProvidedInterfaceBigComponentRequiredInterfaceProvidedInterfaceTinyComponentRequiredInterfaceProvidedInterfaceBComponentRequiredInterfaceProvidedInterfaceMr.ComponentRequi

3、redInterfaceProvidedInterfaceAComponentRequiredInterfaceProvidedInterfaceYetComponentRequiredInterfaceProvidedInterfaceSomeComponentRequiredInterfaceProvidedInterfaceOneComponentRequiredInterfaceProvidedInterfaceMrs.ComponentRequiredInterface…EvenwhenRestrictedbyStyle

4、Whathappenedhere?ProvidedInterfaceLayer4RequiredInterfaceProvidedInterfaceLayer3RequiredInterfaceProvidedInterfaceLayer2RequiredInterfaceProvidedInterfaceLayer1RequiredInterfaceFan-inandFan-outHighfan-inLowfan-outLowfan-inHighfan-outUSUALLYGOOD!USUALLYBAD!ProvidedInte

5、rfaceComponentRequiredInterfaceProvidedInterfaceComponentRequiredInterfaceUSESRelationDefinitionLevel0:thosemodulesthatdonotuseanyothermodulesLeveli:thosemodulesthatuseatleastonemoduleatleveli–1andusenomodulesatleveliorgreaterUseDetermineflexibilityDeterminereuseDeter

6、mineincrementaltestabilityExampleLevel2Level1Level0Level0ProvidedInterfaceBigComponentRequiredInterfaceProvidedInterfaceAComponentRequiredInterfaceProvidedInterfaceTinyComponentRequiredInterfaceProvidedInterfaceYetComponentRequiredInterfaceObservationsTheUSESrelationd

7、oesnotnecessarilyformahierarchyAnacyclicdirectedgraphisgoodCyclesgenerallyarebadIndicationofhighcouplingIndicationofbrokenseparationofconcernsRulesofthumb:allowatouseb……ifitmakesasimpler…ifbisnotonlyusedbyabutalsobyothercomponentsObservationsSomeinvocationsarenotUSESC

8、onsideratransferofcontrolConsideraschedulerinsideaprogramSomeUSESdonotinvolveinvocationsConsiderinterrupthandlersConsiderglo