华东交大软件学院外教课程Lecture-6-Requirements-Engineering

SoftwareEngineering

UsmanFarooq

sf_usman@

Goal(s)ofthislecture

Themainaimofthislectureistounderstandtherequirementsengineeringphaseofsoftwaredevelopmentlifecycle.Wewillfocusonthefollowingsthings:IntroductiontoRequirementsEngineeringTypesofRequirementsRequirementsEngineeringProcess(outputsandinputs)TwoTasksofRERequirementEngineeringProcesses2

RequirementsEngineering(RE)Theprocessofestablishingtheservicesthatthecustomerrequiresfromasystemandtheconstraintsunderwhichitisoperatesandisdeveloped.Therequirementsthemselvesarethedescriptionsofthesystemservicesandconstraintsthataregeneratedorproducedduringtherequirementsengineeringprocess.

FunctionalRequirementsStatementsofservicesthesystemshouldprovide,howthesystemreacttoparticularinputsandhowthesystemshouldbehaveinparticularsituations.LetusconsidertheexampleofHospitalManagementSystem,thefunctionalrequirementsrelatedwiththissystemare:-‘Thesystemshallmaintainthehistoryofallpatientsbothpriorandongoing.’‘Thesystemshallbeabletomanagetheaccessrightsforallusers.’‘Patientrecordshallbeaccessibletoonlyauthorizedusers.’

Non-FunctionalRequirementsInnon-functionalrequirements,themainfocusinonqualityratherthanfunctionality.Theserequirementsarealsocalledqualityrequirements.Letusagainconsidertheexampleofhospitalmanagementsystemforunderstandingnon-functionalrequirements:-“Datashouldnotbelostandnowrongdatashouldbeinsertedintothesystem.”“Thesystemshallbeavailabletotheusers24/7.”“Systemshallsurviveinbothcommunicationorpowerfailure.”“Thesearchtimeforretrievingthepatientrecordshallnotexceed2.5second.”

CostofRequirementsEngineeringItdependsonthetypeandsizeofthesystembeingdeveloped.Thesurveyswhichhavebeencarriedoutsofarsuggestthat,forlargehardware/softwaresystems,about15%ofthebudgetistakenupbyrequirementsengineeringactivities.Forsmallersystemswhicharemostlysoftware,therequirementscostsareusuallylessthanthis,around10%ofthetotalbudgetofthesystem.

Whathappenswhentherequirementsarewrong?Therearenumberofconsequenceswhicharisewhenthesystemrequirementsarewrong:-ThesystemmaybedeliveredlateThesystemcostrisesasexpectedBothcustomerandend-usersarenotsatisfiedwiththesystem.Thesystemmaybeunreliableinuse,withregularsystemerrorsandcrashesdisruptingnormaloperation.Ifthesystemcontinuesinuse,thecostsofmaintainingandevolvingthesystemareveryhigh.

RequirementsEngineeringProcess-InputsandOutputsRequirementsEngineeringProcessExistingsystemsinformationStakeholderneedsOrganizationalstandardsRegulationsDomaininformationSystemspecificationAgreedrequirementsSystemmodels

RequirementsEngineeringProcess-InputsandOutputsREprocess-InputItincludes:1.ExistingsysteminformationInformationaboutthefunctionalityofsystemstobereplacedInformationaboutothersystems,whichinteractwiththesystembeingspecified

RequirementsEngineeringProcess-InputsandOutputs2.StakeholdersneedsDescriptionofwhatsystemstakeholdersneedfromthesystemtosupporttheirwork3.OrganizationalstandardsStandardsusedinanorganizationregardingsystemdevelopmentpractice,qualitymanagement,etc.

RequirementsEngineeringProcess-InputsandOutputs4.RegulationsExternalregulationssuchashealthandsafetyregulations,whichapplytothesystem5.DomaininformationGeneralinformationabouttheapplicationdomainofthesystem

RequirementsEngineeringProcess-InputsandOutputsREprocess-OutputItincludes:1.AgreedrequirementsAdescriptionofthesystemrequirements,whichisunderstandablebystakeholdersandwhichhasbeenagreedbythem.2.SystemspecificationThisisamoredetailedspecificationofthesystem,whichmaybeproducedinsomecases

RequirementsEngineeringProcess-InputsandOutputs3.SystemmodelsAsetofmodelssuchasadata-flowmodel,anobjectmodel,aprocessmodel,etc.,whichdescribesthesystemfromdifferentperspectives

TwoMainTasksofRequirementsEngineeringTherearetwomaintaskswhichneedstobeperformedintherequirementsengineeringprocess.ProblemanalysisAnalysisofasoftwareproblemProductdescriptionCompletespecificationofthedesiredexternalbehaviorofthesoftwaresystemtobebuilt.Alsoknownasfunctionaldescription,functionalrequirements,orspecifications

TwoMainTasksofRequirementsEngineering1.ProblemAnalysisProblemanalysisisthefirstandforemosttaskofrequirementsengineeringprocess.Itincludes:Brainstorming,interviewing,elicitingrequirementsIdentifyingallpossibleconstraintsExpansionofinformationTradingoffconstraintsandorganizinginformationCompleteunderstandingshouldbeachieved

TwoMainTasksofRequirementsEngineering2.ProductDescriptionProductdescriptionisanothertaskofrequirementsengineeringprocess.Inthistaskwe:MakedecisionstodefinetheexternalbehaviorofthesoftwareproductOrganizeideas,resolveconflictingviews,andeliminateinconsistenciesandambiguities

TwoMainTasksofRequirementsEngineering

WhatReallyHappensItshouldbekeptinmindthat:“Bothproblemanalysisandproductdescriptionruninparallelanditerativelythroughouttherequirementsengineeringprocess”

RequirementsEngineeringProcessesorActivities.RequirementsElicitationRequirementsAnalysisandNegotiationRequirementsSpecificationRequirementsValidationUserNeeds,DomainInformation,ExistingSystemInformation,Regulations,Standards,Etc.RequirementsDocumentAgreedRequirements

RequirementsEngineeringProcessesorActivities1.RequirementsElicitationRequirementselicitationactivityisperformedby:Determiningthesystemrequirementsthroughconsultationwithstakeholders,fromsystemdocuments,domainknowledge,andmarketstudiesRequirementsacquisitionorrequirementsdiscovery

RequirementsEngineeringProcessesorActivities2.RequirementsAnalysisandNegotiationRequirementsanalysisandnegotiationactivityisperformedby:-UnderstandingtherelationshipsamongvariouscustomerrequirementsandshapingthoserelationshipstoachieveasuccessfulresultNegotiationsamongdifferentstakeholdersandrequirementsengineersIncompleteandinconsistentinformationneedstobetackledhereSomeanalysisandnegotiationneedstobedoneonaccountofbudgetaryconstraints

RequirementsEngineeringProcessesorActivities3.RequirementsSpecificationRequirementsspecificationincludes:-Buildingatangiblemodelofreq