数据库系统概念全套配套课件PPT ch17.ppt

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1、Chapter17:DatabaseSystemArchitecturesChapter17:DatabaseSystemArchitecturesCentralizedandClient-ServerSystemsServerSystemArchitecturesParallelSystemsDistributedSystemsNetworkTypesCentralizedSystemsRunonasinglecomputersystemanddonotinteractwithothercomputersystems.General-purposecomputersystem:

2、onetoafewCPUsandanumberofdevicecontrollersthatareconnectedthroughacommonbusthatprovidesaccesstosharedmemory.Single-usersystem(e.g.,personalcomputerorworkstation):desk-topunit,singleuser,usuallyhasonlyoneCPUandoneortwoharddisks;theOSmaysupportonlyoneuser.Multi-usersystem:moredisks,morememory,m

3、ultipleCPUs,andamulti-userOS.Servealargenumberofuserswhoareconnectedtothesystemvieterminals.Oftencalledserversystems.ACentralizedComputerSystemClient-ServerSystemsServersystemssatisfyrequestsgeneratedatmclientsystems,whosegeneralstructureisshownbelow:Client-ServerSystems(Cont.)Databasefunctio

4、nalitycanbedividedinto:Back-end:managesaccessstructures,queryevaluationandoptimization,concurrencycontrolandrecovery.Front-end:consistsoftoolssuchasforms,report-writers,andgraphicaluserinterfacefacilities.Theinterfacebetweenthefront-endandtheback-endisthroughSQLorthroughanapplicationprogramin

5、terface.Client-ServerSystems(Cont.)Advantagesofreplacingmainframeswithnetworksofworkstationsorpersonalcomputersconnectedtoback-endservermachines:betterfunctionalityforthecostflexibilityinlocatingresourcesandexpandingfacilitiesbetteruserinterfaceseasiermaintenanceServerSystemArchitectureServer

6、systemscanbebroadlycategorizedintotwokinds:transactionserverswhicharewidelyusedinrelationaldatabasesystems,anddataservers,usedinobject-orienteddatabasesystemsTransactionServersAlsocalledqueryserversystemsorSQLserversystemsClientssendrequeststotheserverTransactionsareexecutedattheserverResults

7、areshippedbacktotheclient.RequestsarespecifiedinSQL,andcommunicatedtotheserverthrougharemoteprocedurecall(RPC)mechanism.TransactionalRPCallowsmanyRPCcallstoformatransaction.OpenDatabaseConnectivity(ODBC)isaClanguageapplicationprograminterface