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1、外文资料DatabaseManagementSystemsAdatabase(sometimesspelleddatabase)isalsocalledanelectronicdatabase,referringtoanycollectionofdata,orinformation,thatisspeciallyorganizedforrapidsearchandretrievalbyacomputer.Databasesarestructuredtofacilitatethestorage,retrieval,modification,anddeletionofdatainc
2、onjunctionwithvariousdata-processingoperations.Databasescanbestoredonmagneticdiskortape,opticaldisk,orsomeothersecondarystoragedevice.Adatabaseconsistsofafileorasetoffiles.Theinformationinthesefilesmaybebrokendownintorecords,eachofwhichconsistsofoneormorefields.Fieldsarethebasicunitsofdatast
3、orage,andeachfieldtypicallycontainsinformationpertainingtooneaspectorattributeoftheentitydescribedbythedatabase.Usingkeywordsandvarioussortingcommands,userscanrapidlysearch,rearrange,group,andselectthefieldsinmanyrecordstoretrieveorcreatereportsonparticularaggregateofdata.Complexdatarelation
4、shipsandlinkagesmaybefoundinallbutthesimplestdatabases.Thesystemsoftwarepackagethathandlesthedifficulttasksassociatedwithcreating,accessing,andmaintainingdatabaserecordsiscalledadatabasemanagementsystem(DBMS).TheprogramsinaDBMSpackageestablishaninterfacebetweenthedatabaseitselfandtheusersoft
5、hedatabase..(Theseusersmaybeapplicationsprogrammers,managersandotherswithinformationneeds,andvariousOSprograms.)ADBMScanorganize,process,andpresentselecteddataelementsformthedatabase.Thiscapabilityenablesdecisionmakerstosearch,probe,andquerydatabasecontentsinordertoextractanswerstononrecurri
6、ngandunplannedquestionsthataren’tavailableinregularreports.Thesequestionsmightinitiallybevagueand/orpoorlydefined,butpeoplecan“browse”throughthedatabaseuntiltheyhavetheneededinformation.Inshort,theDBMSwill“manage”thestoreddataitemsandassembletheneededitemsfromthecommondatabaseinresponsetothe
7、queriesofthosewhoaren’tprogrammers.Adatabasemanagementsystem(DBMS)iscomposedofthreemajorparts:(1)astoragesubsystemthatstoresandretrievesdatainfiles;(2)amodelingandmanipulationsubsystemthatprovidesthemeanswithwhichtoorganizethedataandtoadd,delete,ma