CornellUniversity Compu1ngandInforma1onScience

CS5150So(wareEngineering3.Examplesofso(waredevelopmentprocesses

WilliamY.Arms

DefiniBons:AcBvityandSprint

Ac1vity

AnacBvityisageneraltermforanypartofaprojectthattakesplaceoverBme(alsoknownasatask)

• Eachstepintheso(waredevelopmentprocesscanbebrokendownintoseveralacBviBes.

Sprint

AsprintisasetperiodofBmeduringwhichateamcompletespartofaso(wareproject.

• Eachsprintwillgothroughmostoralloftheprocesssteps.

• Atypicalsprintmighthaveateamof6to8peopleworkingfor2to4weeks.

IteraBveRefinement

Concept •Createaprototypesystemearlyinthedevelopmentprocess. •Reviewtheprototypewithclientsandtestitwithusers,toimprovetheunderstandingoftherequirementsandclarifythedesign.

•RefinetheprototypeinaseriesofiteraBons. RequirementsarehardtounderstandunBlthereisanoperaBonalsystem,parBcularlywithuserinterfaces. Mistakesintherequirementsarethemostexpensivetocorrect. Example: •ConverBnganaBonalarchivefrompaperbasedtocomputerbased.

IteraBveRefinement

Requirements

Design

ImplementaBon

Review

Release

DiscussionofIteraBveRefinement

ThisisamediumweightprocesswithdocumentaBoncreatedduringtheprocess. IteraBverefinementusesvarioustechniquesthatenabletheclienttoreviewthetheplannedsystemearlyduringdevelopment: •Userinterfacemock-up •Throw-awayso(warecomponents •Dummymodules •Rapidprototyping •Successiverefinement Getsomethingworkingasquicklyaspossible,forclientanduserevaluaBon,butdonotreleaseit.

IteraBveRefinementwithaLargeSystem

OutlineDescripBon

Requirements

Design

ImplementaBon

IniBalVersion

IntermediateVersions

FinalVersion

Reviewmaybe

conBnuous

SpiralDevelopment

Spiraldevelopment•Createabasesystemthathastheoverallstructureofthefinalproductwithdummystubsformissingcomponents.

•Createacomprehensivesetoftestcasesforallcompletedcomponents

•Useasuccessionofsprintstodevelopneworimprovedcomponents,eachwithasetoftestcases.Addthesecomponentstothesourcecodelibrary.

•Onadailycycle,buildtheenBresystemfromthesourcecodelibraryandrunthecompletesetoftestcases.

Withspiraldevelopmentthereisalwaysafullytestedsystem,butthefuncBonalityisincomplete.

Example

DevelopinganewversionofanoperaBngsystem.

SpiralDevelopment

Newandimproved

components

Repeateveryday

Sourcecodelibrary

Testlibrary

BuildenBresystemfromsource

RunenBretestsuite

IncrementalReleaseofOnlineSystems

Whenso=wareisreleasedonlineitiso(enpossibletodividethedevelopmentintoasequenceofsprintsthataredevelopedandreleasedinquicksuccession. Example: •Start-upcompanydevelopingawebbasedshoppingservice.Advantages •Pay-backoninvestmentbeginssoon. •Requirementaremoreclearlyunderstoodindevelopingsubsequentsprints–minimizewaste.

•Feedbackfromcustomersandclientscanbeincorporatedinlaterphases.

ItiseasierforasmallteamtodevelopasmallsprintcorrectlythantocoordinatelargeprojectswithmanyramificaBons.

AgileDevelopment(OriginalVersionwithImmediateRelease)

• Theprojectisdividedintoalargenumberofsmalltasks,knownassprints. • Foreachsprint,ateamworksthroughafullso(waredevelopmentcycle

includingplanning,requirementsanalysis,design,coding,tesBng,andacceptancetesBng,andrelease.

• EachsprintiscompletedinafixedBmeperiod,e.g.,fourweeks. • Thesizeofansprintisbasedonteamsize,e.g.,5-10people.

Sprint1

Release Sprint1

Sprint2 Sprint3

Release Sprint2

Release Sprint3

DiscussionofAgileDevelopment

Varia1onsonagileso=waredevelopmentInpracBceitisrarelypossibleforeverysprinttoendwithreleasedso(ware,butso(waredevelopmentbasedonsprintshasmanyadvantages.Modernso(waredevelopmentincludesawiderangeofprocessesthatarecalled“agile”.Otherprocesseswithnamessuchas“heroicprogramming”or“scrum”usemanyofthesameconcepts.Characteris1cs• Developmentofaprojectisdividedintoalargenumberofsprints.• Eachsprintendswithfullytestedcode.• Thisisalightweightprocesswithminimaldocumentationcreatedduringthe

process.Ageneraldefini1on(fromWikipedia) Agileso(waredevelopmentdescribesasetofprinciplesforso(waredevelopmentunderwhichrequirementsandsoluBonsevolvethroughthecollaboraBveeffortofself-organizingcross-funcBonalteams.

AgileDevelopment

A(ereachsprintthecodemaybe:• released(originalagilemethod)• combinedwithcodefromothersprintsforsubsequentrelease• incorporatedintoalargercodebase(spiraldevelopment)

Sprint1

Testedcode

Sprint2 Sprint3

Testedcode

Testedcode

AgileDevelopment:Rework

Thechallengeofagiledevelopment Theagileapproachisexcellentforthedevelopmentorcontinualenhancementofasystemwithinanestablishedarchitecture. Ahigh-levelteammustestablishtheoverallarchitectureandcoordinatethesprints.ReworkWithagiledevelopmenttherequirementsanddesignoftheoverallsystememergeincrementally.• Inevitablypartsofsomeearlysprintswillneedtobereworked.• Thisrequireschangestocodethathasalreadybeenfullytestedandmayhavebeenreleased.Thisisalwaysawkward.

Ifthevolumeofreworkislarge,itismoreefficientnottofullypolisheachcomponent,buttouseiterativerefinementtominimizetheamountofrework.

SequenBalDevelopment:TheWaterfallModel

Requirements

Systemdesign

ProgramtesBng

OperaBon&maintenance

Programdesign

ImplementaBon(coding)

Acceptance&release

Requirements

Design

ImplementaBon

Feasibilitystudy

ThereareproblemswiththisbasicmodelanditisrarelyusedinpracBce.

DiscussionoftheWaterfallModel

ThewaterfallmodelisaheavyweightprocesswithfulldocumentaBonofeachprocessstep. Advantages: •Processvisibility •SeparaBonoftasks •Qualitycontrolateachstep •Costmonitoringateachstep Disadvantages: InpracBce,eachstageintheprocessrevealsnewunderstandingofthepreviousstages,whicho(enrequirestheearlierstagestoberevised. TheWaterfallModelisnotflexibleenough.

DiscussionoftheWaterfallModel

Apuresequen1almodelisimpossible Examples: • AfeasibilitystudycannotcreateaproposedbudgetandschedulewithoutapreliminarystudyoftherequirementsandatentaBvedesign.

• DetaileddesignandimplementaBonrevealgapsintherequirementsspecificaBon.

• Requirementsand/ortechnologymaychangeduringthedevelopment. TheplanmustallowforsomeformofiteraBon.

ModifiedWaterfallModel

Waterfallmodelwithfeedback ThisisbejerRequirements

Systemdesign

ProgramtesBng

OperaBon&maintenance

Programdesign

ImplementaBon(coding)

Acceptance&release

Feasibilitystudy

SequenBalDevelopment

SequenBalprocessesworkbestwhentherequirementsarewellunderstoodandthedesignisstraighkorward,e.g.,•Conversionsofmanualdataprocessingsystemswheretherequirementswerewellunderstoodandfewchangesweremadeduringthedevelopment(e.g.,electricitybilling).

•NewmodelsofaproductwherethefuncBonalityiscloselyderivedfromanearlierproduct(e.g.automaBcbrakingsystemforacar).

•PorBonsofalargesystemwheresomecomponentshaveclearlydefinedrequirementsandareclearlyseparatedfromtherestofthesystem.

Contracts

Noteaboutcontractsforso=waredevelopmentSomeorganizaBonscontractforso(waredevelopmentbyplacingseparatecontractsforeachstageoftheWaterfallModelorarrangeforpaymenta(ereachstage.ThisisaverybadpracBce.

MixedProcesses

InpracBce,manylargeprojectsuseprocessesthatmixaspectsofthefourtypesofso(wareprocess.Forexample:• Withspiraldevelopment,newcomponentsmaybedevelopedusinganyofthethreeothermethods.

• Userinterfaceshavetobetestedwithusers.ThisforcesiteraBvedevelopment,evenwithinanagileorsequenBalprocess.

MixedProcesses:PhasedDevelopment

Combinesequen1alanditera1veelementsAsimplesystemwithbasicfuncBonalityisbroughtquicklyintoproducBon(Phase1).ThissystemmaybedevelopedusingasequenBaloriteraBverefinement.Subsequentphasesarebasedonexperiencegainedfromusersofthepreviousphase.Advantages•Pay-backoninvestmentbeginssoon.•Requirementaremoreclearlyunderstoodwhendevelopingsubsequentphases

ExamplesofMixedProcesses:IteraBveRefinement+WaterfallModel

Problem:Addgraphicspackagetoaprogrammingenvironment Phase1:IteraBverefinement Makeseveralprototypeversionsbyextendingthecurrentenvironmentwithapreprocessorandrun-Bmesupportpackage.TestwithusersunBlusersarepleasedwithfuncBon.Throwthecodeaway. Phase2:Modifiedwaterfall UsetheresultsofPhase1tospecifyaformalsetofrequirements.Writenewcompilerandrun-BmesystemincorporaBnggraphicselements.Makeminoradjustmentstorequirementsasneeded.

CorporateProcesses

Largeso(waredevelopmentorganizaBonshavetheirowninternalprocessesthataredesignedfortheirneeds.Forexample: • Amazon.com(Internetcommerce)makesextensiveuseofsprints.Mostso(waredevelopmentisdividedintoincrementsofaboutfourweekselapsedBme.

• LockheedMarBn(governmentcontractor)followsasequenBalprocessthatfitswiththewaythattheUSgovernmentmanagesso(warecontracts.

• SAP(businessso(ware)emphasizesthefuncBonalitythatisseenbytheirbusinesscustomers.MuchofthedevelopmentissuitableforasequenBalprocess.

•Microso((PCso(ware)placesgreatemphasisontesBngwithaverywidevarietyofequipmentandbackwardcompaBbility.Muchofthedevelopmentusesaspiralprocess.

ChoosingaSo(wareProcess

Changesduringtheso(waredevelopmentprocessareexpensive. • Iftherequirementsarepoorlyunderstood,orexpectedtochange,selecta

processthatkeepsflexibility.IteraBverefinement,agilesprints,phasedimplementaBon.

• Ifabigso(waresystemhasmanyinter-relatedcomponents,avoidmajorchangestothedesignofasystemduringdevelopment.SequenBalprocess,suchasthemodifiedwaterfallmodel.

• Ifthemarketfortheso(wareispoorlyunderstood,useaprocessthatgetsoperaBonalso(wareinfrontofcustomersasquicklyaspossible.Incremental,agilesprints.

ObservaBonsaboutSo(wareProcesses

Completedprojectsshouldhaveincludedallthebasicprocesssteps but...thedevelopmentprocessisalwayspartlyevoluBonary. Riskisloweredby: • Prototypingkeycomponents • Frequentreleases,ordividinglargeprojectsintophases • EarlyandrepeatedtesBngwithusersandcustomers • Followingavisibleso(wareprocess • Makinguseofreusablecomponents Itisneverpossibletocompleteeachstepwithoutprovisionforrevision.Thisisknownasthrowingitoverthewall.

CS5150Projects:IteraBveRefinement

firstpresentaBon

thirdpresentaBon

secondpresentaBon

Requirements

Design

ImplementaBon

Review

Release

CS5150Project:AgileDevelopment

Sprint1

Testedcode

Sprint2 Sprint3

Testedcode

Testedcode

firstpresentaBon secondpresentaBon thirdpresentaBon

ForeachsprintaimtocompleteasecBonofthecode.

CS5150Projects:SequenBalDevelopment

1.Requirements

2.Design

3.ImplementaBon

IfyoufollowasequenBalprocessthethreepresentaBonsshouldbeasshown.

Requirements

Systemdesign

ProgramtesBng

OperaBon&maintenance

Programdesign

ImplementaBon(coding)

Acceptance&release

Feasibilitystudy