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2012
DatabaseManagementSystemSource：DatabaseandNetworkJournalAuthor：DavidAnderson
Youknowthatadataisacollectionoflogicallyrelateddataelementsthatmaybestructuredinvariouswaystomeetthemultipleprocessingandretrievalneedsoforganizationsandindividuals.There’snothingnewaboutdatabase-earlyoneswerechiseledinstone,pennedonscrolls,andwrittenonindexcards.Butnowdatabasearecommonlyrecordedonmagneticallymedia,andcomputerprogramsarerequiredtoperformthenecessarystorageandretrievaloperations.Thesystemsoftwarepackagethathandlesthedifficulttasksassociatedwithcreated,accessing,andmaintainingdatabaserecordsisinaDBMSpackageestablishaninterfacebetweenthedatabaseitselfandtheusersofthedatabase.(Theseusersmaybeapplicationsprogrammers,managersandotherswithinformationneeds,andvariousOSprogrammers.ADBMScanorganize,process,andpresentselecteddataelementsfromthedatabase.Thiscapabilityenablesdecisionmakerstosearch.Probe,andquerydatacontentsinordertoextractanswerstononrecurringandunplannedquestionsthataren’tavailableinregularreports.Thesequestionsmightinitiallybevagueand/orpoorlydefined,butpeoplecan“browse”throughthedatabaseuntiltheyhavetheneededinformation.Inshort,theDBMSwill“manage”thestoreddataitemsandassembletheneededitemsfromthecommondatabaseinresponsetothequeriesofthosewhoaren’tprogrammers.Inafile-orientedsystem,users
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2012
needingspecialinformationmaycommunicatetheirneedstoaprogrammers,who,whentimepermits,willinformation.TheavailabilityofaDBMS,however,offersusersamuchfasteralternativecommunicationspatch(seefigure.Special,direct,andotherfileprocessingapproachesateusedtoorganizeandstructuredatainsinglefiles.ButaDBMSisabletointegratedataelementsfromseveralfilestoanswerspecificuserinquiriesfirinformation.ThismeansthattheDBMSisabletostructureandtietogetherthelogicallyrelateddatafromseverallargefiles.Logicalstructures.Identifyingtheselogicalrelationshipsisajobofthedataadministrator.Adatadefinitionlanguageisusedforthispurpose.TheDBMSmaythenEmployoneofthefollowinglogicalstructuringtechniquesduringstorageaccess,andretrievaloperation:liststructures,hierarchical(treestructures,andnetworkstructures,relationalstructures.1.Liststructures.Inthislogicalapproach,recordsarelinkedtogetherbytheuseofpointers.Apointerisadataiteminonerecordthatidentifiesthestoragelocationofanotherlogicallyrelatedrecord.Recordsinacustomermasterfile,forexample,willcontainthenameandaddressofeachcustomer,andanaccountnumberidentifieseachrecordinthisfile.Duringanaccountingperiod,acustomermaymaintainaninvoicefiletoreflectthesetransactions.Aliststructurecouldbeusedinthissituationtoshowtheunpaidinvoicesatanygiventime.Eachinthe
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