軟件工程第四版第一章

Chapter1WhatisSoftwareEngineeringShariL.PfleegerJoanneM.Atlee4thEditionContents

1.1WhatisSoftwareEngineering?1.2HowSuccessfulHaveWeBeen?1.3WhatIsGoodSoftware?1.4WhoDoesSoftwareEngineering?1.5ASystemsApproach1.6AnEngineeringApproach1.7MembersoftheDevelopmentTeam1.8HowHasSoftwareEngineeringChanged?1.9InformationSystemExample1.10 RealTimeExample1.11 WhatthisChapterMeansforYouObjectivesWhatwemeanbysoftwareengineeringSoftwareengineering’strackrecordWhatwemeanbygoodsoftwareWhyasystemsapproachisimportantHowsoftwareengineeringhaschangedsincethe1970s.1.1WhatisSoftwareEngineering?

SolvingProblemsSoftwareproductsarelargeandcomplexDevelopmentrequiresanalysisandsynthesisAnalysis:decomposealargeproblemintosmaller,understandablepiecesabstractionisthekeySynthesis:build(compose)softwarefromsmallerbuildingblockscompositionischallenging1.1WhatisSoftwareEngineering?

SolvingProblems(continued)Theanalysisprocess1.1WhatisSoftwareEngineering?

SolvingProblems(continued)Thesynthesisprocess1.1WhatisSoftwareEngineering?

SolvingProblems(continued)Method:referstoaformalprocedureTool:aninstrumentorautomatedsystemforaccomplishingsomethinginabetterwayProcedure:acombinationoftoolsandtechniquestoproduceaproductParadigm:philosophyorapproachforbuildingaproduct1.1WhatisSoftwareEngineering?

WhereDoestheSoftwareEngineerFitIn?Computerscience:focusingoncomputerhardwareandprogramminglanguagesSoftwareengineering:focusingoncomputerasaproblem-solvingtool1.1WhatisSoftwareEngineering?

WhereDoestheSWEngineerFitin?(continued)Relationshipbetweencomputerscienceandsoftwareengineering1.2HowSuccessfulHaveWeBeen?PerformtasksmorequicklyandeffectivelyWordprocessing,spreadsheets,e-mailSupportadvancesinmedicine,agriculture,transportation,multimediaeducation,andmostotherindustriesHowever,softwareisnotwithoutproblems1.2HowSuccessfulHaveWeBeen?

Sidebar1.1TerminologyforDescribingBugsAfault:occurswhenahumanmakesamistake,calledanerror,inperformingsomesoftwareactivitiesAfailure:isadeparturefromthesystem’srequiredbehaviour1.2HowSuccessfulHaveWeBeen?

ExamplesofSoftwareFailureIRShiredSperryCorporationtobuildanautomatedfederalincometaxformprocessingprocessAnextra$90Mwasneededtoenhancetheoriginal$103productIRSlost$40.2Moninterestsand$22.3MinovertimewagesbecauserefundswerenotreturnedontimeMalfunctioningcodeinTherac-25killedseveralpeopleReliabilityconstraintshavecausedcancellationofmanysafetycriticalsystemsSafety-critical:somethingwhosefailureposesathreattolifeorhealth1.3WhatIsGoodSoftware?

Sidebar1.2PerspectiveonQualityThetranscendentalview:qualityissomethingwecanrecognizebutnotdefineTheuserview:qualityisfitnessforpurposeThemanufacturingview:qualityisconformancetospecificationTheproductview:qualitytiedtoinherentproductcharacteristicsThevalue-basedview:dependsontheamountthecustomersiswillingtopayforit1.3WhatisGoodSoftware?GoodsoftwareengineeringmustalwaysincludeastrategyforproducingqualitysoftwareThreewaysofconsideringqualityThequalityoftheproductThequalityoftheprocessThequalityoftheproductinthecontextofthebusinessenvironment1.3WhatIsGoodSoftware?

TheQualityoftheProductUsersjudgeexternalcharacteristics(e.g.,correctfunctionality,numberoffailures,typeoffailures)Designersandmaintainersjudgeinternalcharacteristics(e.g.,typesoffaults)ThusdifferentstakeholdersmayhavedifferentcriteriaNeedqualitymodelstorelatetheuser’sexternalviewtodeveloper’sinternalview1.3WhatIsGoodSoftware?

TheQualityoftheProduct(continued)McCall’squalitymodel1.3WhatIsGoodSoftware?

TheQualityoftheProcessQualityofthedevelopmentandmaintenanceprocessisasimportantastheproductqualityThedevelopmentprocessneedstobemodeledModelingwilladdressquestionssuchasWheretofindaparticularkindoffaultHowtofindfaultsearlierHowtobuildinfaulttoleranceWhatarealternativeactivities1.3WhatIsGoodSoftware?

TheQualityoftheProcess(continued)ModelsforprocessimprovementSEI’sCapabilityMaturityModel(CMM)ISO9000SoftwareProcessImprovementandCapabilitydEtermination(SPICE)1.3WhatIsGoodSoftware?

TheQualityintheContextoftheBusinessEnvironmentBusinessvalueisasimportantastechnicalvalueBusinessvalue(inrelationshiptotechnicalvalue)mustbequantifiedAcommonapproach:returnoninvestment(ROI)–whatisgivenupforotherpurposesROIisinterpretedindifferentterms:reducingcosts,predictingsavings,improvingproductivity,andcosts(effortsandresources)1.3WhatIsGoodSoftware?

TheQualityoftheContextoftheBusinessEnvironmentIndustry’sviewofROI1.4WhoDoesSoftwareEngineering?Customer:thecompany,organization,orpersonwhopaysforthesoftwaresystemDeveloper:thecompany,organization,orpersonwhoisbuildingthesoftwaresystemUser:thepersonorpeoplewhowillactuallyusethesystem1.4WhoDoesSoftwareEngineering?(continued)Participants(stakeholders)inasoftwaredevelopmentproject1.5SystemsApproachIdentifyactivitiesandobjectsDefinethesystemboundaryConsidernestedsystems,systemsinterrelationship1.5SystemsApproach

TheElementofaSystemActivitiesandobjectsAnactivityisaneventinitiatedbyatriggerObjectsorentitiesaretheelementsinvolvedintheactivitiesRelationshipsandthesystemboundariesArelationshipdefinestheinteractionamongentitiesandactivitiesSystemboundariesdeterminetheoriginofinputanddestinationsoftheoutput1.5SystemsApproach

TheElementsofaSystem(continued)Exampleofsystems:ahumanrespiratorysystem1.5SystemsApproach

TheElementofaSystem(continued)Acomputersystemmustalsobeclearlydescribed:Systemdefinitionofapaycheckproduction1.5SystemsApproach

InterrelatedSystemsSomesystemsaredependenttoothersystemsTheinterdependenciesmaybecomplexItispossibleforonesystemtoexistinsideanothersystemIftheboundarydefinitionsaredetailed,buildingalargersystemfromthesmalleronesisrelativelyeasy1.5SystemsApproach

InterrelatedSystems(continued)Alayeredsystem1.6EngineeringApproach

BuildingaSystemRequirementsanalysisanddefinitionSystemdesignProgramdesignWritingtheprogramsUnittestingIntegrationtestingSystemtestingSystemdeliveryMaintenance1.7MembersoftheDevelopmentTeamRequirementanalysts:workwiththecustomerstoidentifyanddocumenttherequirementsDesigners:generateasystem-leveldescriptionofwhatthesystemussupposedtodoProgrammers:writelinesofcodetoimplementthedesignTesters:catchfaultsTrainers:showusershowtousethesystemMaintenanceteam:fixfaultsthatshowuplaterLibrarians:prepareandstoredocumentssuchassoftwarerequirementsConfigurationmanagementteam:maintaincorrespondenceamongvariousartifacts1.7MembersoftheDevelopmentTeam(continued)Typicalrolesplayedbythemembersofadevelopmentteam1.8HowHasSoftwareEngineeringChanged?

TheNatureoftheChangeBefore1970sSingleprocessors:mainframesDesignedinoneoftwowaysasatransformation:inputwasconvertedtooutputasatransaction:inputdeterminedwhichfunctionshouldbeperformedAfter1970sRunonmultiplesystemsPerformmulti-functions1.8HowHasSEChanged?

Wasserman'sSevenKeyFactorsCriticalityoftime-to-marketShiftsintheeconomicsofcomputingAvailabilityofpowerfuldesktopcomputingExtensivelocal-andwide-areanetworkingAvailabilityandadoptionofobject-orientedtechnologyGraphicaluserinterfacesUnpredictabilityofthewaterfallmodelofsoftwaredevelopment1.8HowHasSEChanged?

Wasserman'sSevenKeyFactors(continued)Thekeyfactorsthathavechangedthesoftwaredevelopment1.8HowHasSEChanged?

Wasserman'sDisciplineofSoftwareEngineeringAbstractionAnalysisanddesignmethodsandnotationsUserinterfaceprototypingSoftwarearchitectureSoftwareprocessReuseMeasurementToolsandintegratedenvironments1.8HowHasSEChanged?

AbstractionAdescriptionoftheproblematsomelevelofgeneralizationHidedetails1.8HowHasSEChanged?

AnalysisandDesignMethodsandNotationsProvidedocumentationFacilitatecommunicationOffermultipleviewsUnifydifferentviews1.8HowHasSEChanged?

UserInterfacePrototypingPrototyping:buildingasmallversionofasystemHelpusersidentifykeyrequirementsofasystemDemonstratefeasibilityDevelopgooduserinterface1.8HowHasSEChanged?

SoftwareArchitectureAsystem’sarchitecturedescribesthesystemintermsofasetofarchitecturalunitsandrelationshipsbetweentheseunitsArchitecturaldecompositiontechniquesModulardecompositionData-orienteddecompositionEvent-drivendecompositionOutside-in-designdecompositionObject-orienteddecomposition1.8HowHasSEChanged?

SoftwareProcessManyvariationsDifferenttypesofsoftwareneeddifferentprocessesEnterprise-wideapplicationsneedagreatdealofcontrolDepartmentalapplicationscantakeadvantageofrapiddevelopment1.8HowHasSEChanged?

SoftwareProcess(continued)Pictorialrepresentationofdifferencesindevelopmentprocesses1.8HowHasSEChanged?

SoftwareReuseCommonalitiesbetweenapplicationsmayallowreusingartifactsfrompreviousdevelopmentsImproveproductivityReducecostsPotentialconcernsItmaybefastertobuildasmallerapplicationthansearchingforreusablecomponentsGeneralizedcomponentstakemoretimetobuildMustclarifywhowillberesponsibleformaintainingreusablecomponentsGeneralityvsspecificity:alwaysaconflict1.8HowHasSEChanged?

MeasurementUsingmeasurementtohelpfindasolution1.8HowHasSEChanged?

ToolsandIntegratedEnvironmentsPlatformintegration(onheterogeneousnetworks)Presentationintegration(commonalityofuserinterface)Processintegration(linkingtoolsandthedevelopmentprocess)Dataintegration(tosharecommondata)Controlintegration(theabilityofonetooltoinitiateactioninanotherone)1.9InformationSystemExample

PiccadillySystemPiccadillyTelevision:regionalBritishTVfranchiseAdvertisingschemehasmanyconstraints:alcoholadvertsonlyafter9pmifactorinshow,nosameactorinadvertwithin45minutesifadvertinclassofproduct,nootheradvertinsameclassduringsamebreakratesdep