SoftwareEngineering软体工程(英文课件)

1,SoftwareEngineering軟體工程,2,CourseObjectives,TolearnaboutallthedifficultiesindevelopingsoftwaresothatwecanavoidpitfallsandmythsinsoftwaredesignTolearnaboutdifferentsoftwareprocessessothatwecanchooseasuitableoneTolearntodesignhigh-qualityefficientsoftwaresothatitisusableandmaintainableTolearnaboutadvancedmethodsforsoftwareengineering,3,CourseContents,IntroductiontoSoftwareEngineeringSoftwareProcessesRequirementsEngineeringSoftwareDesignObject-OrientedSoftwareDevelopmentSoftwareTestingandVerificationSoftwareProjectManagementAdvancedMethods,4,Chapter1IntroductiontoSoftwareEngineering,Anoverviewofsoftwareengineering,includingsoftwarecrisis,myths,methods,evolution,andstatus,5,Contents,SoftwareCrisisSoftwareMythsWhatisSoftwareEngineeringEvolutionofSoftwareEngineeringState-of-artinSoftwareEngineering,6,ThestatisticsChaosReport,StandishGroup1995365ITexecutivesinUScompaniesindiverseindustrysegments.8,380projects,averagecostoverrun=189%,averagetimeoverrun=222%.,61%oforiginallyspecifiedfeaturesincluded,?,InAverages189%oforiginalbudget221%oforiginalschedule61%oforiginalfunctionality,7,SymptomofSoftwareCrisis,AboutUS$250billionsspentperyearintheUSonapplicationdevelopmentOutofthis,aboutUS$140billionswastedduetotheprojectsgettingabandonedorreworked;thisinturnbecauseofnotfollowingbestpracticesandstandards,Ref:StandishGroup,1996,8,SymptomofSoftwareCrisis,10%ofclient/serverappsareabandonedorrestartedfromscratch20%ofappsaresignificantlyalteredtoavoiddisaster40%ofappsaredeliveredsignificantlylate,Source:3yearstudyof70largec/sapps30Europeanfirms.Compuware(12/95),9,Softwareproducts:failtomeetuserrequirementscrashfrequentlyexpensivedifficulttoalter,debug,enhanceoftendeliveredlateuseresourcesnon-optimally,ObservedProblems,10,WhyistheStatisticssoBad?,MisconceptiononsoftwaredevelopmentSoftwaremyths,e.g.,theman-monthmythFalseassumptionsNotdistinguishingthecodingofacomputerprogramfromthedevelopmentofasoftwareproductSoftwareprogramshaveexponentialgrowthincomplexityanddifficultylevelwithrespecttosize.Theadhocapproachbreaksdownwhensizeofsoftwareincreases.,11,WhyistheStatisticssoBad?,SoftwareprofessionalslackengineeringtrainingProgrammershaveskillsforprogrammingbutwithouttheengineeringmindsetaboutaprocessdisciplineInternalcomplexitiesEssencesandaccidentsmadebyFred.Brooks,12,HowisSoftwareusuallyConstructed,Therequirementsspecificationwasdefinedlikethis,Thedevelopersunderstooditinthatway,Thisishowtheproblemwassolvedbefore.,Thisishowtheproblemissolvednow,Thatistheprogramafterdebugging,Thisishowtheprogramisdescribedbymarketingdept.,This,infact,iswhatthecustomerwanted;-),13,SoftwareMyths(CustomerPerspectives),Ageneralstatementofobjectivesissufficienttogetstartedwiththedevelopmentofsoftware.Missing/vaguerequirementscaneasilybeincorporated/detailedoutastheygetconcretized.Applicationrequirementscanneverbestable;softwarecanbeandhastobemadeflexibleenoughtoallowchangestobeincorporatedastheyhappen.,14,SoftwareMyths(DeveloperPerspectives),Oncethesoftwareisdemonstrated,thejobisdone.,Usually,theproblemsjustbegin!,15,Untilthesoftwareiscodedandisavailablefortesting,thereisnowayforassessingitsquality.,Usually,therearetoomanytinybugsinsertedateverystagethatgrowinsizeandcomplexityastheyprogressthrufurtherstages!,SoftwareMyths(DeveloperPerspectives),16,Theonlydeliverableforasoftwaredevelopmentprojectisthetestedcode.,Thecodeisonlytheexternallyvisiblecomponentoftheentiresoftwarecomplement!,SoftwareMyths(DeveloperPerspectives),17,SoftwareMyths(ManagementPerspectives),Aslongastherearegoodstandardsandclearproceduresinmycompany,Ishouldntbetooconcerned.,Buttheproofofthepuddingisintheeating;notintheRecipe!,18,SoftwareMyths(ManagementPerspectives),Aslongasmysoftwareengineers(!)haveaccesstothefastestandthemostsophisticatedcomputerenvironmentsandstate-of-the-artsoftwaretools,Ishouldntbetooconcerned.,Theenvironmentisonlyoneoftheseveralfactorsthatdeterminethequalityoftheendsoftwareproduct!,19,SoftwareMyths(ManagementPerspectives),Whenmyscheduleslips,whatIhavetodoistostartafire-fightingoperation:addmoresoftwarespecialists,thosewithhigherskillsandlongerexperience-theywillbringtheschedulebackontherails!,Unfortunately,softwarebusinessdoesnotentertainschedulecompactionbeyondalimit!,20,MisplacedAssumptions,Allrequirementscanbepre-specifiedUsersareexpertsatspecificationoftheirneedsUsersanddevelopersarebothgoodatvisualizationTheprojectteamiscapableofunambiguouscommunication,Ref:LarryVaughn,21,UsuallysmallinsizeAuthorhimselfissoleuserSingledeveloperLacksproperuserinterfaceLacksproperdocumentationAdhocdevelopment.,LargeLargenumberofusersTeamofdevelopersWell-designedinterfaceWelldocumentedthatis,theapplicationofengineeringtosoftware.(IEEEStandardComputerDictionary,610.12,ISBN1-55937-079-3,1990),30,WhatisSoftwareEngineering?(ctd),Softwareengineeringisconcernedwiththetheories,methodsandtoolsfordeveloping,managingandevolvingsoftwareproducts.(I.Sommerville,6ed.)Adisciplinewhoseaimistheproductionofqualitysoftware,deliveredontime,withinbudget,andsatisfyingusersneeds.(StephenR.Schach,SoftwareEngineering,2ed.)Multi-personconstructionofmulti-versionsoftware(Parnas,1987),31,Thepracticalapplicationofscientificknowledgeinthedesignandconstructionofcomputerprogramsandtheassociateddocumentationrequiredtodevelop,operateandmaintainthem(B.W.Boehm)Theestablishmentanduseofsoundengineeringprinciplesinordertoobtaineconomicallysoftwarethatisreliableandworksefficientlyonrealmachines(F.L.Bauer),WhatisSoftwareEngineering?(ctd.),32,Thetechnologicalandmanagerialdisciplineconcernedwithsystematicproductionandmaintenanceofsoftwareproductsthataredevelopedandmodifiedontimeandwithincostconstraints(R.Fairley)Adisciplinethatdealswiththebuildingofsoftwaresystemswhicharesolargethattheyarebuiltbyateamorteamsofengineers(Ghezzi,Jazayeri,Mandrioli),WhatisSoftwareEngineering?(ctd.),33,OtherDefinitionsofSoftwareEngineering,“Asystematicapproachtotheanalysis,design,implementationandmaintenanceofsoftware.”(TheFreeOn-LineDictionaryofComputing)“Thesystematicapplicationoftoolsandtechniquesinthedevelopmentofcomputer-basedapplications.”(SueCongerinTheNewSoftwareEngineering)“SoftwareEngineeringisaboutdesigninganddevelopinghigh-qualitysoftware.”(ShariLawrencePfleegerinSoftwareEngineering-TheProductionofQualitySoftware),34,So,SoftwareEngineeringis,Scopestudyofsoftwareprocess,developmentprinciples,techniques,andnotationsGoalsproductionofqualitysoftware,deliveredontime,withinbudget,satisfyingcustomersrequirementsandusersneeds,35,SoftwareProcess,WaterfalllifecyclePrototypingSpiralmodelAutomaticsynthesismodelObject-orientedmodel4GLmodel,36,TraditionalSoftwareEngineering,SoftwareSystems,Data,Function,Behavior,Entity-RelationDiagram,DataFlowDiagram,StateTransitionDiagram,37,Object-OrientedSoftwareEngineering,SoftwareSystems,Function,Object,Behavior,DataFlowDiagram,ClassDiagram,StateChart,38,EvolutionofSoftwareIndustry,IndependentProgrammingServiceSoftwareProductEnterpriseSolutionPackagedSoftwarefortheMass,39,IndependentProgrammingServices(Era1),Feb1955,ElmerKubieandJohnSheldonfoundedCUCtheFirstSoftwareCompanythatdevotedtotheconstructionofsoftwareespeciallyforhardwarecompany.PromotingSoftwareIndustry:twoMajorProjects,SABRE,airlinereservationsystem,$30million.SAGE,airdefensesystem(19491962)700/1000programmersintheUS.$8billion.,40,SoftwareProduct(Era2),1964MartinGoetzdevelopedFlowchartSoftware-AutoflowforRCA,butrejected.SaletothecustomerofRCA&IBM.Developandmarketsoftwareproductsnotspecificallydesignedforaparticularhardwareplatform.MARKIV,apre-runnerforthedatabasemanagementsystem.IBMunbundledsoftwarefromhardware.,41,EnterpriseSolutions(Era3),DietmarHopp.IBMGermanySystems,ApplicationsandProducts(SAP)$3.3billion(1997)SettingupshopinWalldorf,Germany.Markedbytheemergenceofenterprisesolutionsproviders.e.g.Baan1978.Netherlands.$680million(1997)Oracle1977.U.S.LarryEllison.ERP,$45billion(1997),42,PackagedSoftwarefortheMasses(Era4),Softwareproductsforthemasses.1979.VisiCalc,Spreadsheetprogram.August1981:Thedealofthecentury.BillGatesboughtthefirstversionoftheOSfromasmallfirmcalledSeattleComputerProductsfor$50,000withouttellingthemitwasforIBM.ThedevelopmentoftheIBMPC,1981,initiateda4thsoftwareera.PC-basedmass-marketsoftware.Fewadditionalservicesarerequiredforinstallation.Microsoftreachedrevenuesof$11.6billion.PackagedSoftwareProducts,$57billion(1997),43,InternetSoftwareandServices(Era5),Internetandvalue-addedservicesperiod,1994.WwithNetscapesbrowsersoftwarefortheinternet.,44,Object-Oriented,Adhoc,Dataflow-based,Datastructure-based,Controlflow-based,EvolutionofDesignTechniques,45,RelatedKnowledge,46,ITMarket,Hardwareproducts,Hardwaremaintenance,SoftwareProducts&Services,ProcessingServicesandInternetServices,EmbeddedSoftware,ProfessionalService,SoftwareProducts,EnterpriseSolution,PackagedMass-MarketSoftware,47,SoftwareProductsandServices,EnterpriseSolutionsIBMOracleComputerAssociatesSAPHPFujitsuHitachiParametricTechnologyPeopleSoftSiemens,PackagedMars-MarketSoftwareMicrosoftIBMComputerAssociatesAdobeNovellSymantecIntuitAutodeskAppleTheLearningCompany,ProfessionalSoftwareServicesAndersonConsultingIBMEDSCSCScienceApplicationsCapGeminiHpDECFujitsuBSOOrigin,48,SoftwareEngineeringToday?,Organizations“gowithwhathasworkedinthepast”Everyoneistoobusygettingproductoutthedoortospendtimeineducationortrainingoraddressingtheseproblemseffectively“Outofdate”practicesbecomeinstitutionalized,49,SoftwareEngineeringToday?,Fewpeopleknow,orcanintegrate,bestpracticesUnabletoadoptandutilizeprovenmethodologiesintimelyfashionAlthoughsignificantimprovementshavebeenmadeinspecificareas,therapidlyevolvingnatureofthesoftwareindustryhasresultedinlittleoverallimprovementintheoverallsituation.,50,NotCrisis,butaChronicProblem,ThecrisispersistsAfter35yearslater,thesoftware“crisis”isstillwithusMajorproblemsarestillthesame:poorquality(correctness,usability,maintainability,etc)overbudgetdeliveredlate,ornotatallItisnotacrisisbutachronicproblemItbecomesapersistent,chronicconditionthatsoftwareindustryhastofacewith,51,WhatsWrong?,Doessoftwareengineeringhavenoprogressatall?Notquitetrue.Wehaveindeedseenalotofimprovements,e.g.highlevelprogramming,object-orientedtechnology,etc.Butitdoesnotachieveitspromise,why?productionoffault-freesoftware,deliveredontimeandwithinbudget,thatsatisfiestheusersneeds,andiseasytomaintain,etc.,52,AMoreCloseLook,Thecomparisonwith1995sreportdoesshowthatthereissomeprogressinthepasteightyears.,53,So,WhatstheProblem?,Softwareissues:softwareindustryhaschangesalotinthepastyearsEducationissue:moreemphasisonmethodsandtoolsbutlackofsufficienteducationandtrainingonpeopleProcessandqualityissue:therelacksofasetofknownprovenpracticesforsoftwareengineerstofollowwith,54,SoftwareChangesinthePastYears,Changesinsoftwareovertime:grewinsizefrom10sor100soflinesto1000sto1,000,000soflinesofcodeoperatingenvironmentchangedfromsimple“batch”operationstocomplexmultiprogrammingsystems,totime-sharinganddistributedcomputingtotodaysInternetnetworkcomputingenvironment.,55,SoftwareChangesinthePastYears,Ascomputersystems(bothhardwareandsoftware)havebecomelargerandmorecomplex,thesoftwaredevelopmentprocesshasalsobecomemoreandmorecomplexthesimpleartof“programminginthesmall”isnolongercapableofcopingwiththetask.,56,SituationsforSoftwareareDifferentToo,Drivenbyintensemarketforces,includingpersistentpressuretodeliversoftwareonunrealistictimeschedulesRapidlychangingrequirementsPressuresforfastertimetomarketContinuingrapidevolutionofsoftwaremethodologiesandsystemsIntegrationofnewprocessesandtechniquesNeedtore-designmajorsystems,57,SituationsforSoftwareareDifferentToo,Talentshortage:neededsoftwareengineeringskillsofteninshortsupplyWhatevenworseMooreslawmeansalwaystryingnewthingsComplexitymovesintosoftwareCantfindthelimitsexceptbytrialanderror,58,TheSoftwareIndustryToday,Eventhoughmuchisnowknownabout