計算機專業(yè)英語Unit-7-Software-Engineering課件

Unit7SoftwareEngineeringSectionATheSystemsLifeCycleBackgroundKnowledge背景知識同任何事物一樣，一個軟件產(chǎn)品或軟件系統(tǒng)也要經(jīng)歷孕育、誕生、成長、成熟、衰亡等階段，一般稱為軟件生命周期。周期內(nèi)有問題定義、可行性分析、總體描述、系統(tǒng)設計、編碼、調(diào)試和測試、驗收與運行、維護升級到廢棄等階段，這種按時間分程的思想方法是軟件工程中的一種思想原則。典型的幾種生命周期模型有：瀑布模型、增量模型、V型模型和螺旋模型等NewWordsandUsefulExpressionsproportion/pr?'p?r?n/比例,部份,均衡neglect/n?'glekt/忽視,漏做,疏忽sequential/s?'kwen?l/連續(xù)的,有繼的,相續(xù)的discrete/d?'skri?t/不連續(xù)的;離散的overlap/???v??l?p/重疊,重復rigid/'r?d??d/堅硬的;堅固的;嚴格的emphasis/'emf?s?s/強調(diào),重要,加強linear/'l?n??(r)/線的,線狀的,直線的milestone/'ma?lst??n/里程碑;劃時代的事件NewWordsandUsefulExpressionsstable/'ste?bl/穩(wěn)定的,牢固的;可靠的,穩(wěn)重的subsequent/'s?bs?kw?nt/后來的,并發(fā)的intermediate/??nt??mi:di?t/中間的，中級的;

replacewith替代，替換waterfallmodel瀑布模型instone無法改變的counter-argument反駁；抗辯incrementalmodel增量模型spiralmodel螺旋模型ContentsTheWaterfallModel2TheV-ShapedModel4TheSpiralModel5TheIncrementalModel3SystemLifeCycleOverview1SystemLifeCycleOverviewSystemLifeCycle:theprocessbywhichanexistinginformationsystemisreplacedwithanothersystem.SystemLifeCycleStageStages:beginning,ending,somethinggoingoninbetween.End:therequirementtoadapttonewbusinessrequirementsandchangingconditionsistaxedmoreandmore,userswillbegintobecomedissatisfiedwithsystemperformance,andbusinessefficiencywillstarttosuffer.Atthispoint,thelifecycleofthecurrentsystemisabouttoend.SystemLifeCycleStageSoftwareSystemChallengemanysystemsarelate,andmanyareoverbudget.Asignificantproportionofnewsystemsfailtomeettherequirementslaiddownforthem,orareabandonedbeforetheyarecomplete.Manybusinessesneglecttoproperlytraintheirstaffintheuseofnewinformationsystems,andmanysimplydonotunderstandthecapabilitiesandlimitationsofthetechnologyRiskAversionInanefforttoreducetheriskoffailure,thesystemslifecyclebreaksaprojectdownintoaseriesofwell-definedstages,fromtheformulationoftheinitialconceptthroughtotheimplementationandmaintenanceofafullyworkingsystem.ContentsTheWaterfallModel2TheV-ShapedModel4TheSpiralModel5TheIncrementalModel3SystemLifeCycleOverview1TheWaterfallModelConceptasequentialsoftwaredevelopmentmodelsuggestedbyW.W.Royceinwhichdevelopmentisseenasflowingsteadilydownwards(likeawaterfall)throughanumberofphases.TheWaterfallModelCharacteristicsSequential--Youshouldmovetothenextphaseonlywhenthecurrentphaseiscomplete.Discrete--Donotallowforjumpingbackandforth,oranyoverlapbetweenthephases.IdeabehindtheWaterfallModelTimespentearlyoninaprojectmakingsurethattherequirementsanddesignphasesareabsolutelycorrectwillsavemoretimeandeffortlater.Requirementsshouldthereforebesetinstonebeforedesignisstarted,andtheprogram‘sdesignshouldbeperfectbeforeworkbeginsontheimplementationphase."measuretwice,cutonce".SuitableScenarioandUnsuitableScenarioSuitableScenario:projectsthatarestable(i.e.whoserequirementsareunlikelytochangesignificantly)andwherethesystemdesignersareabletoevaluatepotentialproblemsbeforeimplementationbegins.UnsuitableScenario:whenwhatisbeingmeasuredisconstantlychangingduetochangesinrequirementsortheemergenceofmajorunforeseenproblems.VariationofWaterfallModelRoyce'sownfinalmodelallowedfortheresultsofthetestingphasetobefedbackintothedesignphase,andproblemsfromthedesignstagephasetobefedbackintotherequirementsspecificationphase.ContentsTheWaterfallModel2TheV-ShapedModel4TheSpiralModel5TheIncrementalModel3SystemLifeCycleOverview1TheIncrementalModeTheincrementalmodelallowsdifferentpartsofthesystemtobedevelopedseparately,eachwithitsownlifecycleiteration.Iterationincludesarequirementsanalysis,design,implementationandtestingphase.Thefirstiterationusuallyproducesaworkingversionofthesystemonwhichsubsequentiterationsbuild.TheIncrementalModeDiagramMeritsandDemeritsMerits:Iterationcanbecompletedrelativelyquickly,andiseasiertomanage.Demerits:Likethewaterfallmodel,however,eachphaseofiterationmustbecompletedbeforethenextphasecancommence,andtheoverallsystemarchitecturemaybepoorlydefinedintheearlystagesoftheproject.ContentsTheWaterfallModel2TheV-ShapedModel4TheSpiralModel5TheIncrementalModel3SystemLifeCycleOverview1TheV-shapedModelOverviewLikethewaterfallmodel,eachphaseoftheV-Shapedlifecyclemustbecompletedbeforethenextphasebegins.Inthismodel,however,thereismuchmoreemphasisontesting.Testproceduresaredevelopedearlyinthelifecycle.Systemtestingisdesignedtoassesswhethertherequirementsdeterminedduringtherequirementsanalysisphasehavebeenmet.TheV-shapedModelIntegrationTesting&UnitTestingIntegrationtestingisdevelopedduringthehigh-leveldesignphase,whichfocusesontheoverallsystemarchitecture.Unittestingisplannedtoassessthesuccessofthelow-leveldesignphase,whichconcentratesonindividualsystemcomponents.MeritsEasilyunderstoodandwelldefinedphaseswithspecificdeliverables.Thechancesofsuccessareprobablyhigherthanforthewaterfallmodelduetothedevelopmentoftestplansearlyinthecycle,especiallywhereprojectsarerelativelysmallandtherequirementsarewellunderstood.DemeritsThismodellackstheflexibilityoftheincrementalmodelhowever,withnointermediateprototypesproduced.Themodeldoesnotspecifywhatcourseofactionshouldbetakenifsignificantproblemsemergeduringthetestingphases.ContentsTheWaterfallModel2TheV-ShapedModel4TheSpiralModel5TheIncrementalModel3SystemLifeCycleOverview1TheSpiralModelDifferentPhasesSystemrequirementsaregatheredduringtheplanningphaseandalternativesolutionsaregenerated.Theriskanalysisphaseidentifiestheriskassociatedwitheachalternativesolution(forexample,thelikelihoodofacostoverrunorprohibitiveoperatingcosts).Thedevelopmentphaseresultsinaprototype,whichisthenthoroughlyevaluatedintheevaluationstagebeforethenextiterationofthespiralisundertaken.IterationEndConditionThecyclecontinuesitsiterationsu