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SoftwareEngineering
UsmanFarooq
sf_usman@
Goal(s)ofthislecture
TounderstandsoftwareprocessmodelsTounderstandsoftwareprocessactivitiesTounderstandhowtocopewithchangesTounderstandrationalunifiedprocess2
SoftwareProcessesCoherentsetofactivitiesforspecifying,designing,implementingandtestingsoftwaresystems.Insimplewords,asetofactivitiesthatleadstothedevelopmentorproductionofasoftwareproduct.Whenyouworktobuildaproductorsystem,it’simportanttogothroughaseriesofpredictablesteps(roadmap)thathelpsyoucreateatimely,highqualityresult.Theroadmapthatyoufollowiscalleda“softwareprocess.”
SoftwareProcessesTherearemanydifferentkindsofsoftwareprocesses,butallmustincludefouractivitiesthatareimportanttosoftwareengineering:-SoftwareSpecificationSoftwareDesignandImplementationSoftwareValidationSoftwareEvolution4
SoftwareProcessesThereisnoidealprocessandmostorganizationshavedevelopedtheirownsoftwaredevelopmentprocesses.Theselectionofsoftwareprocesseshighlydependsuponthetypeofthesystembeingdeveloped.Forexample:-SafetycriticalsystemrequiresaverystructureddevelopmentprocessThesystemwithrapidlychangingrequirements,alessformal,flexibleprocessisuseful.5
SoftwareProcessesCategorizationTherearetwocategoriesofsoftwareprocesses:-PlanDrivenProcessesAgileProcesses6
GenericSoftwareProcessModelsWaterfallModelSeparateanddistinctphasesofspecificationanddevelopmentIncrementalDevelopmentSpecificationanddevelopmentareinterleavedThesystemisdevelopedasaseriesofversions(increments),witheachversionaddingfunctionalitytothepreviousversion.Reuse-OrientedSoftwareEngineeringThesystemisconstructedorassembledfromexistingcomponents.7
WaterfallModel8
WaterfallModelStagesRequirementsanalysisanddefinitionSystemandsoftwaredesignImplementationandunittestingIntegrationandsystemtestingOperationandmaintenance9
DrawbacksofWaterfallModelInflexiblepartitioningoftheprojectintodistinctstages.ThismakesitdifficulttorespondtochangingcustomerrequirementsTherefore,thismodelisonlysuitablewhenprojectsrequirementsarequitecertaini.e.:-Customersrequirementsarewellknowninadvance.10
IncrementalDevelopment11
IncrementalDevelopmentExploratoryDevelopmentObjectiveistoworkwithcustomersandtoevolveafinalsystemfromaninitialoutlinespecification.Shouldstartwithwell-understoodrequirementsThrow-awayprototypingObjectiveistounderstandthesystemrequirements.Shouldstartwithpoorlyunderstoodrequirements.12
BenefitsofIncrementalDevelopmentCostrelatedwithaccommodatingcustomerrequirementsisminimized.EarlycustomerfeedbackCustomerfeedbackhelpsinidentifyingtheproblemsearlier.Morerapiddeliveryanddeploymentofusefulsoftwaretothecustomerispossible,evenifallthefunctionalityhasnotbeenincluded.13
ProblemswithIncrementalDevelopmentLackofprocessvisibilityasprojectmanagersneedsregulardeliverablestomeasureprogress.Ifsystemisdevelopedquickly,thenitisnotcosteffectivetoproducedocumentsthatreflecteveryversionofthesystem.Systemsareoftenpoorlystructuredbecauseregularchangesaimstocorruptitsstructure.Specialskills(e.g.inlanguagesforrapidprototyping)mayberequired.14
ApplicabilityofIncrementalDevelopmentForsmallormedium-sizeinteractivesystems.Forpartsofthelargesystemse.g.userinterfaceForshortlifetimesystems.Notsuitableforlargeproject.Why?Becauseinlargeprojectstherearedifferentteamsthatdevelopdifferentpartsofthesystem.Largesizeprojectneedsastableframeworkorarchitectureandtheresponsibilitiesofthedifferentteamsworkingonpartsofthesystemneedtobeclearlydefinedwithrespecttothatarchitecture.Soithastobeplannedinadvanceratherthandevelopincrementally.15
Reuse-OrientedSoftwareEngineering16
Reuse-OrientedSoftwareEngineeringBasedonthesystematicreusewheresystemsareintegratedfromexistingcomponentsorCOTS(Commercial-off-the-shelf)systems.ProcessstagesComponentanalysisRequirementsmodificationSystemdesignwithreuseDevelopmentandintegrationThisapproachisbecomingmoreimportantbutstilllimitedexperiencewithit.17
ReuseOrientedSoftwareEngineeringBenefits:Reuseorientedsoftwareengineeringhelpsinsavingdevelopmenttime,cost,budgetandrisksassociatedwithsoftwareprojects.Drawbacks:Requirementscompromisesareinevitableandthismayleadtoasystemthatdoesnotsatisfythecustomerneedsandexpectations.Somecontroloverthesystemevolutionislostasnewversionsofthereusablecomponentsarenotunderthecontroloforganizationusingthem.18
SoftwareProcessActivities1.SoftwareSpecificationorRequirementsEngineeringTheprocessofestablishingwhatservicesarerequiredandtheconstraintsonthesystem’soperationanddevelopment.Importantandcriticalphaseofsoftwaredevelopment.Thisstageifnotdoneproperlyorefficientlywillcreateproblemsinthelaterstagesofsoftwaredevelopmentsuchasdesign,implementationetc.19
StagesofRequirementsEngineeringProcessTherearefourmainstagesofrequirementsengineeringprocess:-FeasibilityStudyRequirementselicitationandanalysisRequirementsspecificationRequirementsvalidation20
StagesofRequirementsEngineeringProcess.21
SoftwareProcessActivities2.SoftwareDesignandImplementationTheprocessofconvertingthesystemspecificationintoanexecutablesystem.SoftwareDesignDesignasoftwarestructurethatrealizesthespecification.ImplementationTranslatethisstructureintoanexecutableprogram.Theactivitiesofdesignandimplementationarecloselyrelatedandmaybeinter-leaved.22
DesignProcessActivitiesArchitecturalDesignAbstractspecificationInterfaceDesignComponentDesignDataStructureDesignAlgorithmDesign23
TheSoftwareDesignProcess.24
DesignMethodsSystematicapproachestodevelopingasoftwaredesign.Thedesignisusuallydocumentedasasetofgraphicalmodels.PossiblemodelsData-flowmodelEntity-relation-attributemodelStructuralmodelObjectmodels.25
ProgrammingandDebuggingTranslatingadesignintoaprogramandremovingerrorsfromthatprogram.Programmingisapersonalactivity-thereisnogenericprogrammingprocess.Programmerscarryoutsomeprogramtestingtodiscoverfaultsintheprogramandremovethesefaultsinthedebuggingprocess.26
TheDebuggingProcess.27
SoftwareProcessActivities4.SoftwareValidationVerificationandvalidationisaimedtoshowthatasystemconformstoitsspecificationandmeetstherequirementsofthesystemcustomer.Includescheckingandreviewprocessesandsystemtesting.Systemtestinginvolvesexecutingthesystemwithtestcasesthatarederivedfromthespecificationnn
oftherealdatatobeprocessedbythesystem.28
TheTestingProcess.29
TheTestingStagesUnitTestingIndividualcomponentsaretestedModuleTestingRelatedcollectionsofdependentcomponentsaretested.Sub-systemTestingModulesareintegratedintosub-systemsandtested.ThefocushereshouldbeoninterfacetestingSystemTestingTestingofthesystemasawhole.Testingofemergentproperties.AcceptanceTestingTestingwithcustomerdatatocheckthatitisacceptable30
TheTestingPhases.31
SoftwareProcessActivities5.SoftwareEvolutionSoftwareisinherentlyflexibleandcanchange.Asrequirementschangethroughchangingbusinesscircumstances,thesoftwarethatsupportsthebusinessmustalsoevolveandchange.Althoughtherehasbeenademarcationbetweendevelopmentandevolution(maintenance)thisisincreasinglyirrelevantasfewerandfewersystemsarecompletelynew.32
SoftwareEvolution33
CopingwithChangeTwoApproachestoreducecostofrework:-ChangeAvoidanceChangeToleranceChangeAvoidanceWherethesoftwareprocessconsistsactivitiesthatcananticipatedpossiblechangesbeforesignificantreworkisrequired.Forexample,aprototypesystemmaybedevelopedtoshowsomeimportantfunctionsorfeaturesofthesystemtocustomers.Theycanexperimentwiththeprototypeandrefinetheirrequirementsbeforecommittingtohighsoftwareproductioncosts.34
CopingwithChangeChangeToleranceWheretheprocessisdesignedsothatchangescanbeaccommodatedatrelativelylowcost.Thisnormallyincludessomesortofincrementaldevelopment.Proposedchangesmaybeimplementedinincrementsthathavenotyetbeendeveloped.Ifthisisimpossible,thenonlyasingleincrementmayhavetobealteredtoincorporatethechange.35
CopingwithChangeCopingwithchangingsystemrequirementsSystemPrototypingIncrementalDelivery36
SoftwarePrototypingRapidsoftwaredevelopmenttovalidaterequirements.Inthepast,thedevelopedsystemwasnormallythoughtofasinferiorinsomewaytotherequiredsystemsofurtherdevelopmentwasrequired.Now,theboundarybetweenprototypingandnormalsystemdevelopmentisblurredandmanysystemsaredevelopedusingandevolutionaryapproach.37
SoftwarePrototypingUsesofsoftware/systemprototypingTheprincipaluseistohelpcustomersanddevelopersunderstandtherequirementsforsystem.Requirementelicitation:UserscanexperimentwithaprototypetoseehowthesystemsupportstheirworkRequirementvalidation:Theprototypecanrevealerrorsandomissionsintherequirements.Prototypingcanbeconsideredasariskreductionactivitywhichreducesrequirementsrisks.38
SoftwarePrototypingBenefitsMisunderstandingsbetweensoftwareusersanddevelopersareexposed.Missingservicesmaybedetectedandconfusingservicesmaybeidentified.Aworkingsystemisavailableearlyintheprocess.Theprototypemayserveasabasisforderivingasystemspecification.39
SoftwarePrototypingProcess40
IncrementalDeliveryRatherthandeliverthesystemasasingledelivery,thedevelopmentanddeliveryisbrokendownintoincrementswitheachincrementdeliveringpartoftherequiredfunctionality.Userrequirementsareprioritizedandthehighestpriorityrequirementsareincludedinearlyincrements.Oncethedevelopmentofanincrementisstarted,therequirementsarefrozenthoughrequirementsforlaterincrementscancontinuetoevolve.41
IncrementalDelivery.42
SpiralModelProcessisrepresentedasaspiralratherthanasasequenceofactivitieswithbacktracking.Eachloopinthespiralrepresentsaphaseintheprocess.Nofi
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