Deriving Functional Specifications from Business R

DerivingFunctionalSpecicationsfromBusinessRequirementswithAmpersandSTEFJOOSTENOpenUniversityoftheNetherlandsOrdinaNVHowdoweknowthatafunctionalspecication(ofsomeinformationsystem)satisestherequire-mentsputforwardbythebusiness?Thispaperproposesamethod,Ampersand,asananswertothisproblem.Italsoproposesanaccompanyingtool,ADL,thatgeneratesdatamodels,ser-vicecataloguesandtheirspecications,toassistrequirementsengineersinproducingasoundfunctionalspecication.Ampersandimprovesthelifeofrequirementsengineersintwoways:itgivesthemthemeanstoprovebusinessrequirementsconsistentandcompleteanditgivesthemseveraldesignartifactstofacilitatetheirdiscussionswithsoftwaredesigners.Thegeneratedfunc-tionalspecicationfeaturesplatformindependenceandprovablecompliancewiththerulesofthebusiness.Inacasestudy,asetofrequirementsispresentedtogetherwiththeformalspecicationgen-eratedfromit.Thisexample,featuringanorder-delivery-invoiceprocess,compliesfullywiththebusinessrules.Ampersandhasbeentriedinvariouspracticalsituationswithpayingcustomersandclassroomexperiencehasshownthatthisapproachcanbetaughttobusinessanalysts.Thisevidencesupportsthefeasibilityfromapractitioner'spointofview.CategoriesandSubjectDescriptors:D.2.2[SoftwareEngineering]:DesignToolsandTech-niques;D.2.10[SoftwareEngineering]:DesignMethodologies;I.1.4[SymbolicandAlgebraicManipulation]:ApplicationsGeneralTerms:Design,LanguagesAdditionalKeyWordsandPhrases:Automateddesign,businessprocesses,businessrules,infor-mationsystemdesign,rulebaseddesign,softwareengineering,requirementsengineering.1.INTRODUCTIONRequirementsdescribetheusersintentionsexpectationsandneeds,butalsodelimittheinformationsystemneededtorealizetheseintentions.Oneofthechallengesofrequirementsengineeringistohowtounifytheinformalprocessofcapturingtheneedsofuserswiththeformalprocessofspecifyinganinformationsystem.Therstrequirescommunicativeskillsandinformaltechniques,thelatterrequiresformaltechniquestoprescribethedesiredpropertiesofaninformationsystemanditscontext.Thispaperproposestotranslatebusinessrequirementsintoafunctionalspecicationbymeansofacompilationprocess.ThataddressesthechallengeinbottomstuPermissiontomakedigital/hardcopyofallorpartofthismaterialwithoutfeeforpersonalorclassroomuseprovidedthatthecopiesarenotmadeordistributedforprotorcommercialadvantage,theACMcopyright/servernotice,thetitleofthepublication,anditsdateappear,andnoticeisgiventhatcopyingisbypermissionoftheACM,Inc.Tocopyotherwise,torepublish,topostonservers,ortoredistributetolistsrequirespriorspecicpermissionand/orafee.c20YYACM0000-0000/20YY/0000-0001$5.00ACMJournalName,Vol.V,No.N,Month20YY,Pages1{27.2
StefJoostentwoways.Onetheuserside,businessrequirementscanbekeptentirelyinnaturallanguage.Onthetechnicalside,thefunctionalspecicationcanbeentirelyformal.Thecompilerguaranteescompliancebetweenthetwo.Thecontributionofthisarticleconsistsofamethod,Ampersand,andanaccom-panyingtool,ADL,bothintendedforrequirementsengineers.Fromagivensetofformallydenedbusinessrequirements,ADLgeneratesafunctionalspecicationconsistingofadatamodel,aservicecatalogue,aformalspecicationoftheser-vices,andafunctionpointanalysis.Newtothisapproachistheuseofrelationalgebraforrequirementselicitation.Eachrequirementisrepresentedasaruleinrelationalgebra,whichservesasaninvarianttobesatisedbythebusiness.Wecalltheserules`businessrule'toindicatethatitisownedandmotivatedbythebusiness.Theone-to-onecorrespondenceofabusinessrequirementwithabusinessruleoerstraceability.ADLtranslatesbusinessrulesbackintothenaturallan-guage,providingadequatefeedbacktotherequirementsengineerforvalidatinghiswork.ADLalsotranslatestheentiresetofrequirementstodesignartifactsthatarerequiredinthesubsequentsoftwareengineeringprocess.Inthisarticleweconsidereveryactivitythatprecedessoftwaredesigntobeinthescopeofrequirementsengineering.Adistinctionismadebetweendescriptiveandprescriptiveactivities[Greenspanetal.1994].Thisarticleusesthewordre-quirementinadescriptivesense,todescribeanexplicitorimplicitneedofusers.Ontheotherhand,thewordspecicationisusedtoprescribepropertiesofasystemtobebuilt.Thephrasefunctionalspecicationdenotesaprescriptionofdesiredfunc-tionality,andanon-functionalspecicationprescribesanyotherdesiredquality,suchasaperformanceproperty,asecurityproperty,oraneciencyproperty.Manyattemptshavebeenmadetoformalizefunctionalspecications,suchasZ[Spivey1992],CSP[Roscoeetal.1997],LOTOS[ISO1987],VDM[Jones1986],Larch[GuttagandHorning1993],butthenumberofattemptstoformalizerequire-mentsarefewerandlessknown[Borgidaetal.1985;?;?].Stillthereareanumberofgoodreasonstoformalizerequirementstoo.ThesereasonsformtherationalefordevelopingAmpersand:|Aformallydenotedrequirementisinherentlyfalsiable.Aninformalrequirementisnotnecessarilyfalsiable,makingitunsurewhethersucharequirementcanbeusedobjectivelyasacriterionofsatisfaction.Aformalstatementthathastobekepttrueduringthelifetimeoftheinformationsystem,providesrequirementsengineerswithanobjectivesatisfactioncriterion.|Requirementsarecompositional.Aspecicationisnot.Addinganddro