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1、DatabaseSystemsforProgrammableLogicControllersInthispaper,weidentifythedatabaseissuesassociatedwithprogrammablelogiccontrollers(PLC),special-purposecomputersusedinscientificandindustrialapplications,e.g.infactoriesinmanufacturingenvironments.Weproposea
2、saPLCdatabasesystemasingle-user,real-time,scalablemain-memory-onlyrelationaldatabasesystemwithatwo-levelarchitecturehavinghistoricaldatamodelingandmanipulationcapabilities,andqueryprocessingtechniquesincorporatingtime-and/orerror-constrainedqueryevalua
3、tion.Werevisetheladderlogiclanguage,themostcommonPLClanguage,toincorporatedatamanipulationlanguageinstructions.WeaddaseparatetimecomponentintothePLCprocessorscantimetohandledatabaseupdates,backup,integrityenforcementanddataarchivalissues.1.Introduction
4、Aprogrammablelogiccontroller(PLC)isaspecial-purposecomputerusedwithinreal-timescientificcomputingsystems,andindustrialcontrolsystems,say,theautomatedcontrolofafactory'smachinery-therunningexampleusedinthispaper.ThispaperisapositionpaperthatproposesaPLC
5、databasesystemanddiscussesitsfeatures.Indoingso,wetouchbaseswithanumberofbasicdatabasetopics,and,thus,frequentlyrefertootherworkfordetails.PLCsaremostlyusedinmanufacturingenvironments-hence,thechoiceofourrunningexample.However,PLCsarealsousedinscientif
6、icapplicationsforsignaldatagatheringandpreliminarydataprocessing.Thus,wethinkthatforsomescientificapplications,aPLCdatabasemayalsoserveasalocal/transientpartofalargerscientificdatabase.Withtherapidadvancesincomputerhardwareandfallingmemoryprices,inrece
7、ntyears,thecapabilitiesofthenewPLCsinthemarketplacehavebeenincreasingdramatically.ThispaperisapositionpaperthatarguesthataPLCsoftwarecannowcontainadatabasesystemtogreatlyincreaseitsfunctionality.WeproposethearchitectureinFigure1asthearchitectureofanenv
8、ironmentwherereal-timedatagathering(frommultiplesensors)andreal-timedatamanipulationtakesplace.WenowlisttheadvantagesofhavingadatabasesystemdirectlyinsideaPLC.(1)DataModelingTechniques:Theinputandoutputbuffersrepresentaratherunorganized
