英文文献《对分布式系统数据库的介绍》.doc

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1、AnIntroductiontoDatabaseSystems1ADatabaseManagementSystem(DBMS)consistsofacollectionofinterrelateddataandasetofprogramstoaccessthosedata.Adatabaseisacollectionofdataorganizedtoservermanyapplicationsefficientlybycentralizingthedataandminimizingredundantdata.TheprimarygoalofaDBMSistoprovideanenviro

2、nmentthatisbothconvenientandefficienttouseinretrievingandstoringdatabaseinformation.Databasesystemsaredesignedtomanagelargebodiesofinformation.Themanagementofdatainvolvesboththedefinitionofstructuresforthestorageofinformationandtheprovisionofmechanismsforthemanipulationofinformationstored,despite

3、systemmustavoidpossibleanomalousresults.Theimportantofinformationinmostorganizations,whichdeterminesthevalueofthedatabase,hasledtothedevelopmentofalargebodyofconceptsandtechniquesforthedatabase,hasledtothedevelopmentofalargebodyofconceptsandtechniquesfortheefficientmanagementofdata.Thetypicalfile

4、-processingsystemissupportedbyaconventionaloperatingsystem.Permanentrecordsarestoredinvariousfiles,anddifferentapplicationprogramsarewrittentoextractrecordsfrom,andtoaddrecordsto,theappropriatefiles.BeforetheadventofDBMSs,organizationstypicallystoredinformationusingsuchsystems.Keepingorganization

5、alinformationinafile-processingsystemhasanumberofmajordisadvantages.Dataredundancyandinconsistency.Dataredundancyisthepresenceofduplicatedatainmultipledatafiles.Sincethefilesandapplicationprogramsarecreatedbydifferentprogrammersoveralongperiod,thevariousfilesarelikelytohavedifferentformatsandthep

6、rogramsmaybewritteninseveralprogramminglanguages.Moreover,thesameinformationmaybeduplicatedinseveralplaces(files).Thisredundancyleadstohigherstorageandaccesscost.Inaddition,itmayleadtodatainconsistency;thatis,thevariouscopiesofthesamedatamaynolongeragree.Difficultyinaccessingdata.Thepointhereisth

7、atconventionalfile-processingenvironmentsdonotallowneededdatatoberetrievedinaconvenientandefficientmanner.Moreresponsivedata-retrievalsystemsmustbedevelopedforgeneraluse.Integrityproblems.Thedatavaluesstoredinthedataba