cs 5150 so(ware engineering 6. requirements analysis€¦ · requirements analysis v. system design...

CornellUniversity Compu1ngandInforma1onScience

CS5150So(wareEngineering6.RequirementsAnalysis

WilliamY.Arms

Requirements

RequirementsdefinethefuncConofthesystemfromtheclient'sviewpoint. •Therequirementsestablishthesystem'sfuncConality,constraints,andgoalsbyconsultaConwiththeclient,customers,andusers.

•Therequirementsmaybedevelopedinaself-containedstudy,ormayemergeincrementally.

•TherequirementsformthebasisforacceptancetesCng. Thedevelopmentteamandtheclientneedtoworktogethercloselyduringtherequirementsphaseofaso(wareproject. •Therequirementsmustbedevelopedinamannerthatisunderstandablebyboththeclientandthedevelopmentstaff.

WhyareRequirementsImportant?

Causesoffailedso>wareprojects Incompleterequirements 13.1% Lackofuserinvolvement12.4%

Lackofresources 10.6%UnrealisCcexpectaCons 9.9%

LackofexecuCvesupport 9.3% Changingrequirements&specificaCons 8.8% Lackofplanning 8.1% Systemnolongerneeded 7.5% Failurestounderstandtherequirementsledthedeveloperstobuildthewrongsystem.

Source:StandishGroup

RequirementsinIteraCveRefinement

TherequirementsarerevisedforeachiteraCon.

Requirements

Design

ImplementaCon

Review

Release

RequirementsintheModifiedWaterfallModel

TherequirementsneedconCnualupdaCngastheprojectconCnues.

Requirements

Systemdesign

ProgramtesCng

OperaCon&maintenance

Programdesign

ImplementaCon(coding)

Acceptance&release

Feasibilitystudy

RequirementswithAgileDevelopment

Eachsprinthasitsownsetofrequirements.

Sprint1 Sprint2 Sprint3

Testedcode

Testedcode

Testedcode

RequirementGoals

•Understandtherequirementsinappropriatedetail. •Definetherequirementsinamannerthatiscleartotheclient.ThismaybeawridenspecificaCon,prototypesystem,orotherformofcommunicaCon.

•Definetherequirementsinamannerthatiscleartothepeoplewhowilldesign,implement,andmaintainthesystem.

•Ensurethattheclientanddevelopersunderstandtherequirementsandtheirimplica1ons.

ManyCS5150projectsusethefirstpresentaConandtheaccompanyingreporttoconfirmtherequirementswiththeclient. "Ourunderstandingofyourrequirementsisthat...”

StepsintheRequirementsPhase

Therequirementspartofaprojectcanbedividedintoseveralstages: •Analysistoestablishthesystem'sservices,constraints,andgoalsbyconsultaConwithclient,customers,andusers.

•ModelingtoorganizetherequirementsinasystemaCcandcomprehensiblemanner.

•Define,record,andcommunicatetherequirements. WithiteraCveandagilemethods,thesestageswillberepeatedseveralCmes.

TheRequirementsProcess

Feasibility study

Analyze

Model

DefineFeasibility report

Recordandcommunicate

Workwiththeclienttounderstandrequirements

OrganizerequirementsinasystemaCcandcomprehensiblemanner

ReportoralternaCvedescripCon(opConal)

RequirementsAnalysis:InterviewswithClients

Clientinterviewsaretheheartoftherequirementsanalysis. Clientsmayhaveonlyavagueconceptofrequirements. •AllowplentyofCme. •Preparebeforeyoumeetwiththeclient. •Keepfullnotes. •Ifyoudonotunderstand,delvefurther,againandagain. •Repeatwhatyouhear. ForyourCS5150projectsyouwillneedtoscheduleseveralmeeCngswithyourclienttoanalyzetherequirements. SmallgroupmeeCngsareo(enmosteffecCve.

RequirementsAnalysis:UnderstandtheRequirements

Understandtherequirementsindepth •Domainunderstanding Example:Manufacturinglightbulbs •Understandingoftherealrequirementsofallstakeholders Stakeholdersmaynothaveclearideasaboutwhattheyrequire,or

theymaynotexpressrequirementsclearly. Theyareo(entooclosetotheoldwayofdoingthings. •Understandingtheterminology Clientso(enusespecializedterminology.Ifyoudonot

understandit,askforanexplanaCon. KeepaskingquesCons,“Whydoyoudothingsthisway?”“Isthisessen8al?”“Whatarethealterna8ves?”

RequirementsAnalysis:NewandOldSystems

AnewsystemiswhenthereisnoexisCngsystem.Thisisrare. AreplacementsystemiswhenasystemisbuilttoreplaceanexisCngsystem. AlegacysystemisanexisCngsystemthatisnotbeingreplaced,butmustinterfacetothenewsystem. Clientso(enconfusethecurrentsystemwiththeunderlyingrequirement. Inrequirementsanalysisitisimportanttodis1nguish: •featuresofthecurrentsystemthatareneededinthenewsystem •featuresofthecurrentsystemthatarenotneededinthenewsystem •proposednewfeatures

RequirementsAnalysis:UnspokenRequirements

Discoveringtheunspokenrequirementsiso(enthemostdifficultpartofdevelopingtherequirements. Examples: •Resistancetochange •DepartmentalfricCon(e.g.,transferofstaff) •Managementstrengthsandweaknesses

RequirementsAnalysis:Stakeholders

Iden1fythestakeholders: Whoisaffectedbythissystem? Client Seniormanagement ProducConstaff CompuCngstaff Customers Users(manycategories) etc.,etc.,etc., Example: Webshoppingsite(shoppers,administraCon,finance,warehouse) CS5150projectsthatbuildwebapplicaConso(enfindthattheadministraCvesystemthatisnotseenbytheusersisbiggerthanthepartofthesitethatisvisibletotheusers.

RequirementsAnalysis:ViewpointAnalysis

ViewpointAnalysis Analyzetherequirementsasseenbyeachgroupofstakeholders. Example:UniversityAdmissionsSystem •Applicants •UniversityadministraCon Admissionsoffice Financialaidoffice Specialoffices(e.g.,athleCcs,development) •Academicdepartments •Compu8ngstaff •Opera8onsandmaintenance

RequirementsAnalysis:SpecialStudies

Understandingtherequirementsmayneedstudies: Marketresearch focusgroups,surveys,compeCCveanalysis,etc. Example:WindowsXPT-shirtthathighlightedApple’sstrengths Technicalevalua1on experiments,prototypes,etc. Example:WindowsXPbootfaster

DefiningandCommunicaCngRequirements

Objec1ves Recordagreementbetweenclientsanddevelopers • ProvideabasisforacceptancetesCng • Providevisibility • BeafoundaConforsystemandprogramdesign • Communicatewithotherteamswhomayworkonorrelyonthissystem

• Informfuturemaintainers

DefiningandCommunicaCngRequirements:RealismandVerifiability

Requirementsmustberealis1c,i.e.,itmustbepossibletomeetthem.Wrong:Thesystemmustbecapableofx(ifnoknowncomputersystemcandoxatareasonablecost).Requirementsmustbeverifiable,i.e.,sincetherequirementsarethebasisforacceptancetesCng,itmustbepossibletotestwhetherarequirementhasbeenmet.Wrong:Thesystemmustbeeasytouse.Right:AJeroneday'straininganoperatorshouldbeabletoinput50ordersperhour.

DefiningandCommunicaCngRequirements:OpCon1–HeavyweightProcesses

Heavyweightso>wareprocessesexpectdetailedspecifica1on • WridendocumentaConthatspecifieseachrequirementindetail. • Carefullycheckedbyclientanddevelopers. • Maybeacontractualdocument. DifficulCes • Timeconsuminganddifficulttocreate. • Timeconsuminganddifficulttomaintain. • CheckingadetailedspecificaConisdifficultandtedious. • Detailsmayobscuretheoverviewoftherequirements.• ClientsrarelyunderstandtheimplicaCons. ThedifficultyofcreaCngandmaintainingadetailedrequirementsspecificaConisoneofthereasonsthatmanyorganizaConsareadractedtolighterweightdevelopmentprocesses.

DefiningandCommunicaCngRequirements:OpCon2–LightweightProcesses

Lightweightprocessesuseaoutlinespecifica1on+othertools • DocumentaCondescribingkeyrequirementsinappropriatedetail. • Reviewedbyclientanddevelopers. Detailsprovidedbysupplementarytools,e.g., • Userinterfacemock-upordemonstraCon. • Models,e.g.,databaseschema,statemachine,etc. ClientsunderstandprototypesandmodelsbederthanspecificaCon • IteraCveorincremental(agile)developmentprocessesallowstheclienttoappreciatewhatthefinalsystemwilldo.

LightweightProcesses(conCnued)

Withlightweightprocesses,experienceandjudgmentareneededtodisCnguishbetweendetailsthatcanbele(forlaterinthedevelopmentprocessandkeyrequirementsthatmustbeagreedwiththeclientearlyintheprocess. Exampleswheredetailedspecifica1onsareusuallyneeded • Businessrules(e.g.,referencetoanaccounCngstandard) • Legalrestraint(e.g.,lawsonretenConofdata,privacy) • Dataflow(e.g.,sourcesofdata,datavalidaCon) Acommonfaultistomisscrucialdetails.Thisresultsinmisunderstandingsbetweentheclientandthedevelopers.YetthewholeintentoflightweightprocessesistohaveminimalintermediatedocumentaCon.

RequirementsinGovernmentSystems

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GovernmentsystemsintheUSAandabroadhaveareputaConforpoorfuncConalitycombinedwithdelaysandcostover-runs.MypersonalopinionisthatthemethodofcontracCngisamajorcontributortotheseproblems.• Responsibleuseoftaxpayers’moneyleadstocontractsinwhicheachsub-processhasadefineddeliverableatanagreedprice.

• InparCcularmostcontractsdemandadetailedrequirementspecificaConbeforethecontractfordesignandimplementaConareplaced.

• Thisleadstoawaterfallmodelofdevelopment,o(enwithpenalCesformodificaConsoftherequirements.

Butinmanygovernmentsystemstherequirementsarenotwellunderstood.• TheyshoulduseadevelopmentprocessinwhichtherequirementsareflexibleandthedesignevolvesiteraCvely.

• Contractsforsuchdevelopmentprocessesaredifficulttowrite,buttheyleadtobederso(ware.

FuncConalRequirements

Func1onalrequirementsdescribethefuncConsthatthesystemmustperform.TheyareidenCfiedbyanalyzingtheusemadeofthesystemandincludetopicssuchas: • FuncConality •Data •Userinterfaces

Non-FuncConalRequirements

Requirementsthatarenotdirectlyrelatedtothefunc1onsthatthesystemmustperform Productrequirements performance,reliability,portability,etc... OrganizaConalrequirements delivery,training,standards,etc... Externalrequirements legal,interoperability,etc... MarkeCngandpublicrelaCons Example: IntheNSDL,theclient(theNaConalScienceFoundaCon)wantedalivesystemthatcouldbedemonstratedtoseniormanagerssixmonthsa(erthegrantwasawarded.

ExampleofNon-FuncConalRequirements

Example:LibraryofCongressRepository Usetechnologythattheclient'sstaffarefamiliarwith: • Hardwareandso(waresystems(IBM/Unix) • Databasesystems(Oracle) • Programminglanguages(CandC++) Recognizethattheclientisafederallibrary • RegulaConscoveringgovernmentsystems,e.g.,accessibilityto

peoplewithdisabiliCes • Importanceofdevelopingasystemthatwouldberespectedby

othermajorlibraries

Requirements:NegoCaConwiththeClient

Somerequestsfromtheclientmayconflictwithothers:Recognizeandresolveconflicts (e.g.,funcConalityv.costv.Cmeliness)Example: WindowsXPbootfaster:shorterCme-outv.recognizeallequipmentonbus

Requirements:NegoCaConwiththeClient

SomeCmestheclientwillrequestfuncConalitythatisveryexpensiveorimpossible.Whatdoyoudo? •Talkthroughtherequirementwiththeclient.Whyisitwanted?IsthereanalternaCvethatisequivalent?

•Explainthereasoningbehindyourconcern.Explainthetechnical,organizaConal,andcostimplicaCons.

•BeopentosuggesCons.Isthereagapinyourunderstanding?Perhapsasecondopinionmightsuggestotherapproaches.

BeforetherequirementsphaseiscompletedtheclientanddevelopmentteammustresolvethesequesCons. Example NaConalScienceFoundaCongrantsystem,clientaskedforeveryformatthathadeverbeenusedinproposals(e.g.,scienCficsamples).A(ernegoCaCon,agreedthatthefirstphasewouldsupportonlyPDF.

RequirementsAnalysisv.SystemDesign

Dilemmaabouttechnicaldecisions • RequirementsanalysisshouldmakeminimalassumpConsaboutthesystemdesign.

• ButtherequirementsdefiniConmustbeconsistentwithcompuCngtechnologyandtheresourcesavailable.

InpracCce,analysisanddesignareinterwoven.However: 1.Donotallowassump8onsaboutthedesigntoinfluencethe

requirementsanalysis. 2.Donottoallowtherequirementsanalysistoprejudgethesystemdesign.