软件工程导论绪论

AnIntroductiontoSoftwareEngineering,Objectives,IntroducesoftwareengineeringandtoexplainitsimportanceSetouttheanswerstokeyquestionsaboutsoftwareengineering,FAQsaboutsoftwareengineering,Whatissoftwareengineering?Whatisthedifferencebetweensoftwareengineering,computerscience,andsystemsengineering?Whatisthesoftwarecrisis?Whatarethecostsofsoftwareengineering?Whatissoftwareandwhataretheattributesofgoodsoftware?Whatisasoftwareprocessandasoftwareprocessmodel?Whataresoftwareengineeringmethods?WhatisCASE(Computer-AidedSoftwareEngineering)Whatarethekeychallengesfacingsoftwareengineering?,Whatissoftwareengineering?,“Theestablishmentanduseofsoundengineeringprinciplesinordertoobtaineconomicallybuiltsoftwarethatisreliableandworksefficientlyonrealmachines.”,“SoftwareEngineering:(1)Theapplicationofasystematic,disciplines,quantifiableapproachtothedevelopment,operation,andmaintenanceofsoftware;thatistheapplicationofengineeringtosoftware.(2)Thestudyofapproachesasin(1).”,IEEEDefinition(1993),ClassicDefinition(1969),FromWikipedia,“Softwareengineeringistheapplicationofasystematic,disciplined,quantifiableapproachtothedevelopment,operation,andmaintenanceofsoftware.,SoftwareEngineeringvs.ComputerScience,Computerscienceisconcernedwiththeoryandfundamentals;softwareengineeringisconcernedwiththepracticalitiesofdevelopinganddeliveringusefulsoftware.Computersciencetheoriesarestillinsufficienttoactasacompleteunderpinningforsoftwareengineering(unlikee.g.physicsandelectricalengineering).,SoftwareEngineeringvs.ComputerScience,COMPUTERSCIENCE,CUSTOMER,SOFTWAREENGINEERING,Theories,ComputerFunctions,Problem,ToolsandTechniquestoSolveProblem,Softwarevs.Hardware,Youcantsee,touch,orfeelsoftwareSoftwareisonlyengineered,notmanufacturedSoftwaredoesntwearoutSoftwareiscomplexSoftwareisadifferentiatorSoftwarecanbehavelikeanagingfactory,Communicationisacriticalelement.,SoftwareEngineeringvs.SystemEngineering,Systemengineeringisconcernedwithallaspectsofcomputer-basedsystemsdevelopmentincludinghardware,softwareandprocessengineering.Softwareengineeringispartofthisprocessconcernedwithdevelopingthesoftwareinfrastructure,control,applicationsanddatabasesinthesystem.Systemengineersareinvolvedinsystemspecification,architecturaldesign,integrationanddeployment.,WhattoStudyinSoftwareEngineering?,ProductsproducedProcessesusedtoproducetheproducts,Thefinalproductsaresoftwarecomponents.Theymaybefullyexecutablescomponents,programs,modules,systems,orsimplymethods.Therearemanysoftwaredeliverablesbetweenthespecificationoftheproductsandtheactualproducts.,Thesoftwaredevelopmentlifecycledescribesthedevelopmentprocessforproducingsoftwareproducts.Howevertherearemanyotheritemswithintheprocess.Wewillinvestigatethefullprocessofsoftwareengineering.,Somecorequestions,Whatisthesoftwareproduct?Whodoessoftwareengineeringoftheproduct?Whyissoftwareimportant?Whatarethestepsinsoftwareengineering?Whatistheworkproductoftheengineeringprocess?Howdoweensureproductsarebuiltcorrectlyandthatthecorrectproductisbuilt?,ProblemsBehindthe“SoftwareCrisis”,IncreasedsizeandcomplexityofsystemsCostoverrunsDesignbugsafterimplementationMaintenancerippleeffectRequirementsanddesignneededdevelopmenttools,notjustintheprogrammingtools,SoftwareCrisis,ResearchfromStandishGroupDataon9236developmentprojectscompletedin2004.,AbandonedorCancelledProjects,SoftwareCrisis,2002surveyofinformationtechnologyorganizationsbyCutterConsortiumData78%havebeeninvolvedindisputesendinginlitigationIn67%ofthedisputes,thefunctionalityoftheinformationsystemasdelivereddidnotmeetuptotheclaimsofthedevelopersIn56%ofthedisputes,thepromiseddeliverydateslippedseveraltimesIn45%ofthedisputes,thedefectsweresoseverethattheinformationsystemwasunusable,NewAspectsofCrisis,(In)security-wehaveallowedourselvestobecometoodependentonsoftware(andhardware)thatwasneverdesignedtoberobustorsecureOvercomplexity-competitionformorefeatures,easeofuse,andintegrationaremakingproductstoolargetocomprehendandmaintainInternationalizationthisisaproblemfortheUS,whichhasbeenpresumptuouslycomplacentaboutitsleadershipSoftwarepatents-theselegallandminesarebeginningtochokethesoftwareindustryRapidchangestowerofBabel,multicore,etc.,WeaponsAgainstSoftwareCrisis,ImprovingsoftwareengineeringmethodologiesHigh-levellanguagesandtoolsthatencourageandenforcetheseprinciples,SoftwareEngineeringDefinition,Thesoftwarecrisisyieldedyetanotherdefinitionofsoftwareengineering:Disciplinewhoseaimistheproductionoffault-freesoftware,deliveredontimeandwithinbudget,thatsatisfiestheclientsneeds.,CostsofSoftwareEngineering,Softwarecostsdominatecomputersystemscosts.Roughly60%ofcostsaredevelopmentcosts,40%aretestingcosts.Forcustomsoftware,evolutioncostsoftenexceeddevelopmentcosts.Softwaremaintenancecostsaremorethansoftwaredevelopmentcosts.Forsystemswithalonglifethemaintenancemaybeseveraltimesthedevelopmentcosts.Andoftenevenbadsoftwarehasalonglife.,CostsofSoftwareEngineering,Costsvarydependingonthetypeofsystembeingdeveloped.Thecostsdependoftherequirementsofsystemattributessuchasperformanceandsystemreliabilityaswellasthecomplexityofthetypeofsystembeingdeveloped.Distributionofcostsdependsonthedevelopmentmodelthatisused.,Activitycostdistribution,Productdevelopmentcosts,MaintenanceCosts,(a)Between1976and1981(b)Between1992and1998,ChangingViewofMaintenance,PostdeliverymaintenanceDevelopment-then-maintenancemodelTemporaldefinitionModernmaintenanceOccurswheneverafaultisfixedortherequirementschange,irrespectiveofwhetherittakesplacebeforeorafterinstallationoftheproduct,WhySoCostly?,TocorrectafaultearlyinthelifecycleUsuallyjustadocumentneedstobechangedTocorrectafaultlateinthelifecycleChangethecodeandthedocumentationTestthechangeitselfPerformregressiontestingReinstalltheproductontheclientscomputer(s),Wearvs.Deterioration,RogerS.Pressman,SoftwareEngineering:APractitionersApproach,FourthEdition1997,TheCostofChange,RogerS.Pressman,Chapter1Page19,SoftwareEngineering:APractitionersApproach,FourthEdition1997,WhatisaSoftwareProduct?,Asetofitemsorobjectscalledaconfiguration.Itincludesthingslike:MultipleseparateprogramsConfigurationfileswhichareusedtosetuptheseprogramsSystemdocumentationwhichdescribesthestructureofthesystemDeveloperandUserdocumentationwhichexplainshowtousethesystemDataforthesystemWebsitesforuserstodownloadrecentproductinformation,Whatissoftware?,Computerprogramsandassociateddocumentationsuchasrequirements,designmodelsandusermanuals.Softwareproductsmaybedevelopedforaparticularcustomerormaybedevelopedforageneralmarket.Newsoftwarecanbecreatedbydevelopingnewprograms,configuringgenericsoftwaresystemsorreusingexistingsoftware.,Whatissoftware?,SoftwareproductsmaybeGENERICdevelopedtobesoldtoarangeofdifferentcustomerse.g.PCsoftwaresuchasExcelorWord.referredtoascommercialoff-the-shelf(COTS)softwareorclickwaresuppliedbyavendorBESPOKE(custom)-developedforasinglecustomeraccordingtotheirspecification.Productspecificationcontrolledbytheproductdeveloper,SoftwareTerminology,Open-sourcesoftwareDevelopedandmaintainedbyateamofvolunteersMaybedownloadedandusedfreeofchargeExamples:LinuxoperatingsystemFirefoxwebbrowserApachewebserver,SoftwareTypes,systemsoftwarereal-timesoftwarebusinesssoftwareengineering/scientificsoftwareembeddedsoftwarePCsoftwareAIsoftwareWebApps(Webapplications),Whataretheattributesofgoodsoftware?,Thesoftwareshoulddelivertherequiredfunctionalityandperformancetotheuserandshouldbemaintainable,dependableandacceptable.MaintainabilitySoftwaremustevolvetomeetchangingneeds;DependabilitySoftwaremustbetrustworthy;EfficiencySoftwareshouldnotmakewastefuluseofsystemresources;AcceptabilitySoftwaremustacceptedbytheusersforwhichitwasdesigned.Thismeansitmustbeunderstandable,usableandcompatiblewithothersystems.,Whataretheattributesofgoodsoftware?,FromtheUsersPerspectiveCorrectnessReliabilityEfficiencyMaintainabilityUsabilityRobustnessFromtheDevelopersPerspectiveConsistencyUnderstandabilityTestabilityCompactnessCompatibilityIntegrity,SoftwareProcess,AsetofactivitiesandassociatedresultswhichproduceasoftwareproductIncorporatesasoftwarelife-cyclemodel,techniques,thetoolsused,andthesoftwaredevelopers,Whatisasoftwareprocessmodel?,Asimplifiedrepresentationofasoftwareprocess,presentedfromaspecificperspective.ExamplesofprocessperspectivesareWorkflowperspective-sequenceofactivities;Data-flowperspective-informationflow;Role/actionperspective-whodoeswhat.GenericprocessmodelsWaterfall;Iterativedevelopment;Component-basedsoftwareengineering.,SoftwareLife-cycleModels,Specifiesthevariousphasesofthesoftwareprocessandtheorderinwhichtheyaretobecarriedout.CoveredinChapter1Dennis,Whataresoftwareengineeringmethods?,Structuredapproachestosoftwaredevelopmentwhichincludesystemmodels,notations,rules,designadviceandprocessguidance.ModeldescriptionsDescriptionsofgraphicalmodelswhichshouldbeproduced;RulesConstraintsappliedtosystemmodels;RecommendationsAdviceongooddesignpractice;ProcessguidanceWhatactivitiestofollow.,WhatisCASE?,Computer-AidedSoftwareEngineeringSoftwaresystemsthatareintendedtoprovideautomatedsupportforsoftwareprocessactivities.CASEsystemsareoftenusedformethodsupport.Upper-CASEToolstosupporttheearlyprocessactivitiesofrequirementsanddesign;Lower-CASEToolstosupportlate