Give me all I pay for — Execution Guarantees in Electronic Commerce Payment Processes

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GivemeallIpayfor—ExecutionGuaranteesinElectronicCommercePaymentProcesses

HeikoSchuldtAndreiPopoviciHans-J¨orgSchekDatabaseResearchGroupInstituteofInformationSystemsETHZentrum,8092Z¨urich,SwitzerlandEmail:schuldt,popovici,schek@inf.ethz.ch

AbstractElectronicCommerceovertheInternetisoneofthemostrapidlygrowingareasintodaysbusiness.However,consideringthemostimportantphaseofElectronicCommerce,thepayment,ithastobenotedthatinmostcurrentlyexploitedapproaches,supportforatleastoneoftheparticipantsislimited.Fromageneralpointofview,acoupleofrequirementsforcorrectpaymentinteractionsexist,namelydifferentlevelsofatomicityintheexchangeofmoneyandgoodsofasinglecustomerwithdifferentmerchants.Inthispaper,weidentifythedifferentrequirementsparticipantsdemandonElectronicCommercepaymentsfromthepointofviewofexecutionguaranteesandpresenthowpaymentinteractionscanbeimplementedbytransactionalprocesses.Finally,weshowhowtheseexecutionguaranteescanbeprovidedforpaymentprocessesinanaturalwaybyapplyingtheideasoftransactionalprocessmanagementtoanElectronicCommercePaymentCoordinator.

1IntroductionAlongwiththeenormousproliferationoftheInternet,ElectronicCommerce(E-Commerce)iscontinu-ouslygainingimportance.ThespectrumofapplicationsthataresubsumedunderthetermE-CommerceleadsfromrathersimpleordersperformedbyEmailtothepurchaseofshoppingbasketsconsistingofseveralgoodsoriginatingfromdifferentmerchantsbyspendingelectroniccashtokens.Remarkably,E-Commerceisaveryinterdisciplinaryresearcharea.Asexistingapproachesarepow-eredbydifferentcommunities(i.e.,cryptography,networking,etc.),theyareveryheterogeneousinnatureandthusalwaysfocusondifferentspecialproblems.Fromthepointofviewofthedatabasecommunity,atomicitypropertieshavebeenidentifiedasonekeyrequirementforpaymentprotocolsinE-Commerce[Tyg96,Tyg98].Themorecomplexinteractionswithconsumersandmerchantsbecome,themoredimen-sionsofatomicityhavetobeaddressed.Inthesimplestcase,onlymoneyhastobetransferredatomicallyfromtheconsumertothemerchant.However,consideringcomplexshoppingbasketsfilledwith(elec-tronic)goodsfromseveralmerchants,atomicitymayalsoberequiredforthepurchaseofallthesegoodsoriginatingfromdifferentpossiblyindependentandautonomoussources,alongwiththeatomicexchangeofmoneyandallgoods.Duetotheirdistributednature,protocolsthathavebeensuggestedtosupportpaymentatomicityinE-Commerceimposehighrequirementsontheparticipatinginstances(e.g.,NetBill[CTS95]).However,withacentralizedpaymentcoordinator,thecomplexinteractionsofthevariousparticipantscanbeembeddedwithinapaymentprocess,thusreducingtheprerequisitesformerchantsandcustomerstoparticipateinE-Commerce.Transactionalprocessmanagement[SAS99]canthenbeexploitedinordertoprovidethenecessaryexecutionguaranteesfortransactionalE-Commercepaymentprocessesinanaturalway.Thispaperisstructuredasfollows:InSection2,weprovideageneralframeworkforE-Commercepaymentinteractions.Basedonthisframework,weanalyzethedifferentatomicityrequirementsforE–Commercepayment(Section3).Then,inSection4,wesummarizetransactionalprocessmanagementand

1presentthestructureofatransactionalpaymentprocessallowingtherequiredexecutionguaranteestobeprovidedbyaPaymentCoordinator.Section5finallyconcludesthepaper.

2SchemaforPaymentProtocolsinE-CommerceThedescriptionofsalesinteractionsinnon-electronicmarkets[Sch98]encompassesthreephases:infor-mation,negotiation,andpayment.Duringtheinformationphase,acustomerevaluatesandcomparestheoffersofseveralmerchants.Afterselectingthebestoffer,shenegotiateswiththechosenmerchanttheconditionsforthedeal(negotiation).Iftheyreachanagreement,thelaststep(thepayment)involvesthemoneytransferfromcustomertomerchantandtheservice(themerchantfulfillshiscontract).Mostelectronicpaymentsystemsfocusonlyonthemoneytransferofthelastphase.Ourviewofanelectronicpaymentschemealsoconsidersthesystemsandprotocolsforaccomplishingboththemoneytransferandtheservice.

2.1ParticipantsAnelectronicpaymentschemeinvolvesparticipantsoriginatingfromtwodistinctworlds:ontheInternetsidetherearethecustomer,themerchantandathirdentity,thepaymentserverwhichcoordinatesthetwo.Theothersideisrepresentedbythefinancialworldwithitsproprietarynetworkinfrastructureandprotocols.Theparticipantsarefinancialinstitutesandagainthepaymentserver,thathastoconsistentlytransformthedataflowontheInternetsideincorresponding“realworld”moneyflow.TheparticipantsaredepictedinFigure1.

2.2StepsofanE-CommerceTransactionPriortothepaymenttransaction,theparticipantsareinvolvedinaninitializationphase,depictedinFigure1bydashedarrows.Bothcustomerandmerchanthavetoestablishaccountswithinthefinancialinstitutes“issuer”(or“acquirer”,resp.).Thetransformationofelectronicmoneyintorealmoneyisperformedusingtheseaccounts.Alsointhisphasethecustomerreceivesfromhisbankacustomersecretwhichenableshimtoperformelectronicpayments.Thecustomersecretisvisibleonlyforthecustomerherself,fortheissuingbankand(eventually)forthepaymentserver.Themostcommonformofthecustomersecretisacreditcardnumber,inelectroniccashschemes(suchaseCash[Dig99]),thecustomersecretisanE-cashtoken.Becauseaccountoperationsareratherlessoftenthanpayments,wecanconsiderthemaspartoftheinitializationphase.Almostallthepaymentschemescontainthefivefollowingsteps,markedinFigure1: