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1、外文资料DatabaseManagementSystemsAdatabase(sometimesspelleddatabase)isalsocalledanelectronicdatabase,referringtoanycollectionofdata,orinformation,thatisspeciallyorganizedforrapidsearchandretrievalbyacomputer.Databasesarestructuredtofacilitatethestorage,retrieval,modification,anddele
2、tionofdatainconjunctionwithvariousdata-processingoperations.Databasescanbestoredonmagneticdiskortape,opticaldisk,orsomeothersecondarystoragedevice.Adatabaseconsistsofafileorasetoffiles.Theinformationinthesefilesmaybebrokendownintorecords,eachofwhichconsistsofoneormorefields.Fiel
3、dsarethebasicunitsofdatastorage,andeachfieldtypicallycontainsinformationpertainingtooneaspectorattributeoftheentitydescribedbythedatabase.Usingkeywordsandvarioussortingcommands,userscanrapidlysearch,rearrange,group,andselectthefieldsinmanyrecordstoretrieveorcreatereportsonpartic
4、ularaggregateofdata.Complexdatarelationshipsandlinkagesmaybefoundinallbutthesimplestdatabases.Thesystemsoftwarepackagethathandlesthedifficulttasksassociatedwithcreating,accessing,andmaintainingdatabaserecordsiscalledadatabasemanagementsystem(DBMS).TheprogramsinaDBMSpackageestabl
5、ishaninterfacebetweenthedatabaseitselfandtheusersofthedatabase..(Theseusersmaybeapplicationsprogrammers,managersandotherswithinformationneeds,andvariousOSprograms.)ADBMScanorganize,process,andpresentselecteddataelementsformthedatabase.Thiscapabilityenablesdecisionmakerstosearch,
6、probe,andquerydatabasecontentsinordertoextractanswerstononrecurringandunplannedquestionsthataren’tavailableinregularreports.Thesequestionsmightinitiallybevagueand/orpoorlydefined,butpeoplecan“browse”throughthedatabaseuntiltheyhavetheneededinformation.Inshort,theDBMSwill“manage”t
7、hestoreddataitemsandassembletheneededitemsfromthecommondatabaseinresponsetothequeriesofthosewhoaren’tprogrammers.Adatabasemanagementsystem(DBMS)iscomposedofthreemajorparts:(1)astoragesubsystemthatstoresandretrievesdatainfiles;(2)amodelingandmanipulationsubsystemthatprovidestheme
8、answithwhichtoorganizethedataandtoadd,delete,ma
