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1、DatabaseManagementSystemSource：DatabaseandNetworkJournalAuthor：DavidAndersonYouknowthatadataisacollectionoflogicallyrelateddataelementsthatmaybestructuredinvariouswaystomeetthemultipleprocessingandretrievalneedsoforganizationsandindividuals.There’snothingnewaboutdatabase-earlyoneswe
2、rechiseledinstone,pennedonscrolls,andwrittenonindexcards.Butnowdatabasearecommonlyrecordedonmagneticallymedia,andcomputerprogramsarerequiredtoperformthenecessarystorageandretrievaloperations.Thesystemsoftwarepackagethathandlesthedifficulttasksassociatedwithcreated,accessing,andmaint
3、ainingdatabaserecordsisinaDBMSpackageestablishaninterfacebetweenthedatabaseitselfandtheusersofthedatabase.(Theseusersmaybeapplicationsprogrammers,managersandotherswithinformationneeds,andvariousOSprogrammers.)ADBMScanorganize,process,andpresentselecteddataelementsfromthedatabase.Thi
4、scapabilityenablesdecisionmakerstosearch.Probe,andquerydatacontentsinordertoextractanswerstononrecurringandunplannedquestionsthataren’tavailableinregularreports.Thesequestionsmightinitiallybevagueand/orpoorlydefined,butpeoplecan“browse”throughthedatabaseuntiltheyhavetheneededinforma
5、tion.Inshort,theDBMSwill“manage”thestoreddataitemsandassembletheneededitemsfromthecommondatabaseinresponsetothequeriesofthosewhoaren’tprogrammers.Inafile-orientedsystem,usersneedingspecialinformationmaycommunicatetheirneedstoaprogrammers,who,whentimepermits,willinformation.Theavaila
6、bilityofaDBMS,however,offersusersamuchfasteralternativecommunicationspatch(seefigure).Special,direct,andotherfileprocessingapproachesateusedtoorganizeandstructuredatainsinglefiles.ButaDBMSisabletointegratedataelementsfromseveralfilestoanswerspecificuserinquiriesfirinformation.Thisme
7、ansthattheDBMSisabletostructureandtietogetherthelogicallyrelateddatafromseverallargefiles.Logicalstructures.Identifyingtheselogicalrelationshipsisajobofthedataadministrator.Adatadefinitionlanguageisusedforthispurpose.TheDBMSmaythenEmployoneofthefollowinglogicalstructuringtechniquesd
8、uringstorageaccess,
