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1、ANOVERVIEWOFREAL-TIMEDATABASESYSTEMS1;22BenKaoandHectorGarcia-Molina1PrincetonUniversity,PrincetonNJ08544,USA2StanfordUniversity,StanfordCA94305,USA1IntroductionTraditionally,real-timesystemsmanagetheirdata(e.g.chambertemperature,aircraftlocations)inapplicationdependentstructures.Asreal-ti
2、mesystemsevolve,theirapplicationsbecomemorecomplexandrequireaccesstomoredata.Itthusbecomesnecessarytomanagethedatainasystematicandorganizedfashion.Databasemanagementsystemsprovidetoolsforsuchorganization,soinrecentyearstherehasbeeninterestinmerging"databaseandreal-timetech-nology.Theresul
3、tingintegratedsystem,whichprovidesdatabaseoperationswithreal-timeconstraintsisgenerallycalledareal-timedatabasesystem(RTDBS)[1].Likeaconventionaldatabasesystem,aRTDBSfunctionsasarepositoryofdata,providesecientstorage,andperformsretrievalandmanipulationofinfor-mation.However,asapartofareal
4、-timesystem,whosetasks"areassociatedwithtimeconstraints,aRTDBS,hastheaddedburdenofensuringsomedegreeofcon denceinmeetingthesystem'stimingrequirements.Exampleapplicationsthathandlelargeamountsofdataandhavestringenttimingrequirementsincludetelephoneswitching(e.g.translatingan800numberintoan
5、actualnumber),radartrackingandothers.Arbitragetrading,forexam-ple,involvestradingcommoditiesindi erentmarketsatdi erentprices.Sincepricediscrepanciesareusuallyshort-lived,automatedsearchingandprocessingoflargeamountsoftradinginformationareverydesirable.Inordertocapitalizeontheopportunities
6、,buy-selldecisionshavetobemadepromptly,oftenwithatimeconstraintsothatthe nancialoverheadinperformingthetradeactionsarewellcompensatedbythebene tresultingfromthetrade.Asanotherexam-ple,aradarsurveillancesystemdetectsaircraftimages"orradarsignatures".Theseimagesarethenmatchedagainstadataba
7、seofknownimages.Theresultofsuchmatchisusedtodriveothersystemactions,forexample,inchoosingacombatstrategy.Conventionaldatabasesystemsarenotadequateforthistypeofapplication.Theydi erfromaRTDBSinmanyaspects.MostimportantlyRTDBSshavedi erentperformancegoals,correc
