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