高级软件工程课件第一章ch01

,AnIntroductiontoSoftwareEngineering,Objectives,TointroducesoftwareengineeringandtoexplainitsimportanceTosetouttheanswerstokeyquestionsaboutsoftwareengineeringTointroduceethicalandprofessionalissuesandtoexplainwhytheyareofconcerntosoftwareengineers,Topicscovered,FAQsaboutsoftwareengineeringProfessionalandethicalresponsibility,Softwareengineering,TheeconomiesofALLdevelopednationsaredependentonsoftware.MoreandmoresystemsaresoftwarecontrolledSoftwareengineeringisconcernedwiththeories,methodsandtoolsforprofessionalsoftwaredevelopment.ExpenditureonsoftwarerepresentsasignificantfractionofGNPinalldevelopedcountries.,Softwarecosts,Softwarecostsoftendominatecomputersystemcosts.ThecostsofsoftwareonaPCareoftengreaterthanthehardwarecost.Softwarecostsmoretomaintainthanitdoestodevelop.Forsystemswithalonglife,maintenancecostsmaybeseveraltimesdevelopmentcosts.Softwareengineeringisconcernedwithcost-effectivesoftwaredevelopment.,FAQsaboutsoftwareengineering,Whatissoftware?Whatissoftwareengineering?Whatisthedifferencebetweensoftwareengineeringandcomputerscience?Whatisthedifferencebetweensoftwareengineeringandsystemengineering?Whatisasoftwareprocess?Whatisasoftwareprocessmodel?,FAQsaboutsoftwareengineering,Whatarethecostsofsoftwareengineering?Whataresoftwareengineeringmethods?WhatisCASE(Computer-AidedSoftwareEngineering)Whataretheattributesofgoodsoftware?Whatarethekeychallengesfacingsoftwareengineering?,Whatissoftware?,Computerprogramsandassociateddocumentationsuchasrequirements,designmodelsandusermanuals.Softwareproductsmaybedevelopedforaparticularcustomerormaybedevelopedforageneralmarket.SoftwareproductsmaybeGeneric-developedtobesoldtoarangeofdifferentcustomerse.g.PCsoftwaresuchasExcelorWord.Bespoke(custom)-developedforasinglecustomeraccordingtotheirspecification.Newsoftwarecanbecreatedbydevelopingnewprograms,configuringgenericsoftwaresystemsorreusingexistingsoftware.,Whatissoftwareengineering?,Softwareengineeringisanengineeringdisciplinethatisconcernedwithallaspectsofsoftwareproduction.Softwareengineersshouldadoptasystematicandorganisedapproachtotheirworkanduseappropriatetoolsandtechniquesdependingontheproblemtobesolved,thedevelopmentconstraintsandtheresourcesavailable.,Whatisthedifferencebetweensoftwareengineeringandcomputerscience?,Computerscienceisconcernedwiththeoryandfundamentals;softwareengineeringisconcernedwiththepracticalitiesofdevelopinganddeliveringusefulsoftware.Computersciencetheoriesarestillinsufficienttoactasacompleteunderpinningforsoftwareengineering(unlikee.g.physicsandelectricalengineering).,Whatisthedifferencebetweensoftwareengineeringandsystemengineering?,Systemengineeringisconcernedwithallaspectsofcomputer-basedsystemsdevelopmentincludinghardware,softwareandprocessengineering.Softwareengineeringispartofthisprocessconcernedwithdevelopingthesoftwareinfrastructure,control,applicationsanddatabasesinthesystem.Systemengineersareinvolvedinsystemspecification,architecturaldesign,integrationanddeployment.,Whatisasoftwareprocess?,Asetofactivitieswhosegoalisthedevelopmentorevolutionofsoftware.Genericactivitiesinallsoftwareprocessesare:Specification-whatthesystemshoulddoanditsdevelopmentconstraintsDevelopment-productionofthesoftwaresystemValidation-checkingthatthesoftwareiswhatthecustomerwantsEvolution-changingthesoftwareinresponsetochangingdemands.,Whatisasoftwareprocessmodel?,Asimplifiedrepresentationofasoftwareprocess,presentedfromaspecificperspective.ExamplesofprocessperspectivesareWorkflowperspective-sequenceofactivities;Data-flowperspective-informationflow;Role/actionperspective-whodoeswhat.GenericprocessmodelsWaterfall;Iterativedevelopment;Component-basedsoftwareengineering.,Whatarethecostsofsoftwareengineering?,Roughly60%ofcostsaredevelopmentcosts,40%aretestingcosts.Forcustomsoftware,evolutioncostsoftenexceeddevelopmentcosts.Costsvarydependingonthetypeofsystembeingdevelopedandtherequirementsofsystemattributessuchasperformanceandsystemreliability.Distributionofcostsdependsonthedevelopmentmodelthatisused.,Activitycostdistribution,Productdevelopmentcosts,Whataresoftwareengineeringmethods?,Structuredapproachestosoftwaredevelopmentwhichincludesystemmodels,notations,rules,designadviceandprocessguidance.ModeldescriptionsDescriptionsofgraphicalmodelswhichshouldbeproduced;RulesConstraintsappliedtosystemmodels;RecommendationsAdviceongooddesignpractice;ProcessguidanceWhatactivitiestofollow.,WhatisCASE(Computer-AidedSoftwareEngineering),Softwaresystemsthatareintendedtoprovideautomatedsupportforsoftwareprocessactivities.CASEsystemsareoftenusedformethodsupport.Upper-CASEToolstosupporttheearlyprocessactivitiesofrequirementsanddesign;Lower-CASEToolstosupportlateractivitiessuchasprogramming,debuggingandtesting.,Whataretheattributesofgoodsoftware?,Thesoftwareshoulddelivertherequiredfunctionalityandperformancetotheuserandshouldbemaintainable,dependableandacceptable.MaintainabilitySoftwaremustevolvetomeetchangingneeds;DependabilitySoftwaremustbetrustworthy;EfficiencySoftwareshouldnotmakewastefuluseofsystemresources;AcceptabilitySoftwaremustacceptedbytheusersforwhichitwasdesigned.Thismeansitmustbeunderstandable,usableandcompatiblewithothersystems.,Whatarethekeychallengesfacingsoftwareengineering?,Heterogeneity,deliveryandtrust.HeterogeneityDevelopingtechniquesforbuildingsoftwarethatcancopewithheterogeneousplatformsandexecutionenvironments;DeliveryDevelopingtechniquesthatleadtofasterdeliveryofsoftware;TrustDevelopingtechniquesthatdemonstratethatsoftwarecanbetrustedbyitsusers.,Professionalandethicalresponsibility,Softwareengineeringinvolveswiderresponsibilitiesthansimplytheapplicationoftechnicalskills.Softwareengineersmustbehaveinanhonestandethicallyresponsiblewayiftheyaretoberespectedasprofessionals.Ethicalbehaviourismorethansimplyupholdingthelaw.,Issuesofprofessionalresponsibility,ConfidentialityEngineersshouldnormallyrespecttheconfidentialityoftheiremployersorclientsirrespectiveofwhetherornotaformalconfidentialityagreementhasbeensigned.CompetenceEngineersshouldnotmisrepresenttheirlevelofcompetence.Theyshouldnotknowinglyacceptworkwhichisoutwiththeircompetence.,Issuesofprofessionalresponsibility,IntellectualpropertyrightsEngineersshouldbeawareoflocallawsgoverningtheuseofintellectualpropertysuchaspatents,copyright,etc.Theyshouldbecarefultoensurethattheintellectualpropertyofemployersandclientsisprotected.ComputermisuseSoftwareengineersshouldnotusetheirtechnicalskillstomisuseotherpeoplescomputers.Computermisuserangesfromrelativelytrivial(gameplayingonanemployersmachine,say)toextremelyserious(disseminationofviruses).,ACM/IEEECodeofEthics,TheprofessionalsocietiesintheUShavecooperatedtoproduceacodeofethicalpractice.Membersoftheseorganisationssignuptothecodeofpracticewhentheyjoin.TheCodecontainseightPrinciplesrelatedtothebehaviourofanddecisionsmadebyprofessionalsoftwareengineers,includingpractitioners,educators,managers,supervisorsandpolicymakers,aswellastraineesandstudentsoftheprofession.,Codeofethics-preamble,PreambleTheshortversionofthecodesummarizesaspirationsatahighleveloftheabstraction;theclausesthatareincludedinthefullversiongiveexamplesanddetailsofhowtheseaspirationschangethewayweactassoftwareengineeringprofessionals.Withouttheaspirations,thedetailscanbecomelegalisticandtedious;withoutthedetails,theaspirationscanbecomehighsoundingbutempty;together,theaspirationsandthedetailsformacohesivecode.Softwareengineersshallcommitthemselvestomakingtheanalysis,specification,design,development,testingandmaintenanceofsoftwareabeneficialandrespectedprofession.Inaccordancewiththeircommitmenttothehealth,safetyandwelfareofthepublic,softwareengineersshalladheretothefollowingEightPrinciples:,Codeofethics-principles,PUBLICSoftwareengineersshallactconsistentlywiththepublicinterest.CLIENTANDEMPLOYERSoftwareengineersshallactinamannerthatisinthebestinterestsoftheirclientandemployerconsistentwiththepublicinterest.PRODUCTSoftwareengineersshallensurethattheirproductsandrelatedmodificationsmeetthehighestprofessionalstandardspossible.,Codeofethics-principles,JUDGMENTSoftwareengineersshallmaintainintegrityandindependenceintheirprofessionaljudgment.MANAGEMENTSoftwareengineeringmanagersandleadersshallsubscribetoandpromoteanethicalapproachtothemanagementofsoftwaredevelopmentandmaintenance.PROFESSIONSoftwareengineersshalladvancetheintegrityandreputationoftheprofessionconsistentwiththepublicinterest.,Codeofethics-principles,COLLEAGUESSoftwareengineersshallbefairtoandsupportiveoftheircolleagues.SELFSoftwareengineersshallparticipateinlifelonglearningregardingthepracticeoftheirprofessionandshallpromoteanethicalapproachtothepracticeoftheprofession.,Ethicaldilemmas,Disagreementinprinciplewiththepoliciesofseniormanagement.Youremployeractsinanunethicalwayandreleasesasafety-criticalsystemwithoutfinishingthetestingofthesystem.Participationinthedevelopmentofmilitaryweaponssystemsornuclearsystems.,Keypoints,Softwareengineeringisanengin