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Chapter4Softwareprototyping•4.1Phototypinginsoftwareprocess•4.2Phototypingtechniques•4.3Userintercasephototyping•Keypo

ints4.1Prototypinginthesoftwareprocess•EvolutionaryprototypingAnapproachtosystemdevelopmentwhereaninitialprototypeisproducedandrefinedthro

ughanumberofstagestothefinalsystem.•Throw-awayprototypingAprototypewhichisusuallyapracticalimplementationofthesystemisproducedtoh

elpdiscoverrequirementsproblemsandthendiscarded.Thesystemisthendevelopedusingsomeotherdevelopmentpro

cess.Prototypingobjectives•Theobjectiveofevolutionaryprototypingistodeliveraworkingsystemtoend-users

.Thedevelopmentstartswiththoserequirementswhicharebestunderstood.•Theobjectiveofthrow-awayprototypingistovalidateor

derivethesystemrequirements.Theprototypingprocessstartswiththoserequirementswhicharepoorlyunderstood

.4.1.1Evolutionaryprototyping•Mustbeusedforsystemswherethespecificationcannotbedevelopedinadvancee.g.AIsystemsanduserinterface

systems.•Basedontechniqueswhichallowrapidsystemiterations.•Verificationisimpossibleasthereisnospecification.V

alidationmeansdemonstratingtheadequacyofthesystem.Evolutionaryprototypingadvantages•AccelerateddeliveryofthesystemRapiddeliveryand

deploymentaresometimesmoreimportantthanfunctionalityorlong-termsoftwaremaintainability.•UserengagementwiththesystemNotonlyisthesystem

morelikelytomeetuserrequirements,theyaremorelikelytocommittotheuseofthesystem.Evolutionaryprototyping•Specification,designandimplementationareinter-t

wined.•Thesystemisdevelopedasaseriesofincrementsthataredeliveredtothecustomer.•TechniquesforrapidsystemdevelopmentareusedsuchasCASEtool

sand4GLs.•UserinterfacesareusuallydevelopedusingaGUIdevelopmenttoolkit.Evolutionaryprototypingproblems•Managementproblems1.Existingmanagementpr

ocessesassumeawaterfallmodelofdevelopment.2.Specialistskillsarerequiredwhichmaynotbeavailableinalldevelopmentte

ams.•MaintenanceproblemsContinualchangetendstocorruptsystemstructuresolong-termmaintenanceisexpensive.•ContractualproblemsPrototypesasspecifica

tions•Somepartsoftherequirements(e.g.safety-criticalfunctions)maybeimpossibletoprototypeandsodon’tappearinthespecification.•Animplementationhasno

legalstandingasacontract.•Non-functionalrequirementscannotbeadequatelytestedinasystemprototype.Incrementald

evelopment•Systemisdevelopedanddeliveredinincrementsafterestablishinganoverallarchitecture.•Requirementsandspecificationsf

oreachincrementmaybedeveloped.•Usersmayexperimentwithdeliveredincrementswhileothersarebeingdeveloped.therefore,theseserveasaformofprototypesystem

.•Intendedtocombinesomeoftheadvantagesofprototypingbutwithamoremanageableprocessandbettersystemstructur

e.4.1.2Throw-awayprototyping•Usedtoreducerequirementsrisk.•Theprototypeisdevelopedfromaninitialspecificatio

n,deliveredforexperimentthendiscarded.•Thethrow-awayprototypeshouldNOTbeconsideredasafinalsystem.1.Somesystemcharacteristicsmayhavebeenleftout.2.Th

ereisnospecificationforlong-termmaintenance.3.Thesystemwillbepoorlystructuredanddifficulttomaintain.Pr

ototypedelivery•Developersmaybepressurisedtodeliverathrow-awayprototypeasafinalsystem.Thisisnotrecommended1.Itmaybeimpossibletotunetheprototype

tomeetnon-functionalrequirements.2.Theprototypeisinevitablyundocumented.3.Thesystemstructurewillbedegradedthroughchangesmadeduringdevelop

ment.4.Normalorganisationalqualitystandardsmaynothavebeenapplied.4.2Rapidprototypingtechniques•Varioustechniqu

esmaybeusedforrapiddevelopment1.Dynamichigh-levellanguagedevelopment.2.Databaseprogramming.3.Componentandapplicationassembly.

•Thesearenotexclusivetechniques-theyareoftenusedtogether.•Visualprogrammingisaninherentpartofmostprototypedevelopmentsystems.4

.2.1Dynamichigh-levellanguages•Languageswhichincludepowerfuldatamanagementfacilities.•Needalargerun-timesupportsystem.Notnormallyusedf

orlargesystemdevelopment.•SomelanguagesofferexcellentUIdevelopmentfacilities.•Somelanguageshaveanintegratedsupportenvironmentwhosefacilitiesmaybe

usedintheprototype.Choiceofprototypinglanguage•Whatistheapplicationdomainoftheproblem?•Whatuserinteractioni

srequired?•Whatsupportenvironmentcomeswiththelanguage?•Differentpartsofthesystemmaybeprogrammedindifferentlanguages.However,theremaybeproblem

swithlanguagecommunications.4.2.2Databaseprogramminglanguages•Domainspecificlanguagesforbusinesssystemsbasedaroundadatabasemanagementsy

stem.•Normallyincludeadatabasequerylanguage,ascreengenerator,areportgeneratorandaspreadsheet.•Maybein

tegratedwithaCASEtoolset.•Thelanguage+environmentissometimesknownasafourth-generationlanguage(4GL).•Cost-effectivefors

malltomediumsizedbusinesssystems.4.2.3Componentandapplicationassembly•Prototypescanbecreatedquicklyfrom

asetofreusablecomponentsplussomemechanismto‘glue’thesecomponenttogether.•Thecompositionmechanismmustincludecontrolfacilitiesandamechanismforcompone

ntcommunication.•Thesystemspecificationmusttakeintoaccounttheavailabilityandfunctionalityofexistingcomponents

.Prototypingwithreuse•Applicationleveldevelopment1.Entireapplicationsystemsareintegratedwiththeprototypesothattheirfuncti

onalitycanbeshared.2.Forexample,iftextpreparationisrequired,astandardwordprocessorcanbeused.•Componentleveldevelopment1.Individualcomponentsareint

egratedwithinastandardframeworktoimplementthesystem.2.FrameworkcanbeascriptinglanguageoranintegrationframeworksuchasCORBAComp

ounddocuments•Forsomeapplications,aprototypecanbecreatedbydevelopingacompounddocument.•Thisisadocumentwithactiveelements(suchasaspreadsheet)that

allowusercomputations.•Eachactiveelementhasanassociatedapplicationwhichisinvokedwhenthatelementisselected.•Thedocumentitselfistheintegratorforthediff

erentapplications.Visualprogramming•ScriptinglanguagessuchasVisualBasicsupportvisualprogrammingwheretheprototypeisdevelopedbycreating

auserinterfacefromstandarditemsandassociatingcomponentswiththeseitems.•Alargelibraryofcomponentsexiststosupportthistypeofdevelopment.•Thes

emaybetailoredtosuitthespecificapplicationrequirements.Problemswithvisualdevelopment•Difficulttocoordinateteam-baseddevelopment.•Noexplici

tsystemarchitecture.•Complexdependenciesbetweenpartsoftheprogramcancausemaintainabilityproblems.4.3Userin

terfaceprototyping•Itisimpossibletopre-specifythelookandfeelofauserinterfaceinaneffectiveway.prototypingisessential.•UIdevelop

mentconsumesanincreasingpartofoverallsystemdevelopmentcosts.•Userinterfacegeneratorsmaybeusedto‘draw’theint

erfaceandsimulateitsfunctionalitywithcomponentsassociatedwithinterfaceentities.•Webinterfacesmaybeprototypedusingawebsiteeditor.Keypoints•Aprototyp

ecanbeusedtogiveend-usersaconcreteimpressionofthesystem’scapabilities.•Prototypingisbecomingincreasinglyusedforsys

temdevelopmentwheredevelopmentisessential.•Throw-awayprototypingisusedtounderstandthesystemrequirements.•Inevolutionaryprototyping,thesystemisdevelo

pedbyevolvinganinitialversiontothefinalversion.•Rapiddevelopmentofprototypesisessential.Thismayrequireleavingoutfunction

alityorrelaxingnon-functionalconstraints.•Prototypingtechniquesincludetheuseofveryhigh-levellanguages,databaseprogrammingandprototypeconstructio

nfromreusablecomponents.•Prototypingisessentialforpartsofthesystemsuchastheuserinterfacewhichcannotbeeffe

ctivelypre-specified.Usersmustbeinvolvedinprototypeevaluation.