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1、外文资料DatabaseManagementSystemsAdatabase(sometimesspelleddatabase)isalsocalledanelectronicdatabase,referringtoanycollectionofdata,orinformation,thatisspeciallyorganizedforrapidsearchandretrievalbyacomputer.Databasesarestructuredtofacilitatethestorage,retrieval,modification,anddeletionofdatainconju
2、nctionwithvariousdata-processingoperations.Databasescanbestoredonmagneticdiskortape,opticaldisk,orsomeothersecondarystoragedevice.Adatabaseconsistsofafileorasetoffiles.Theinformationinthesefilesmaybebrokendownintorecords,eachofwhichconsistsofoneormorefields.Fieldsarethebasicunitsofdatastorage,an
3、deachfieldtypicallycontainsinformationpertainingtooneaspectorattributeoftheentitydescribedbythedatabase.Usingkeywordsandvarioussortingcommands,userscanrapidlysearch,rearrange,group,andselectthefieldsinmanyrecordstoretrieveorcreatereportsonparticularaggregateofdata.Complexdatarelationshipsandlink
4、agesmaybefoundinallbutthesimplestdatabases.Thesystemsoftwarepackagethathandlesthedifficulttasksassociatedwithcreating,accessing,andmaintainingdatabaserecordsiscalledadatabasemanagementsystem(DBMS).TheprogramsinaDBMSpackageestablishaninterfacebetweenthedatabaseitselfandtheusersofthedatabase..(The
5、seusersmaybeapplicationsprogrammers,managersandotherswithinformationneeds,andvariousOSprograms.)ADBMScanorganize,process,andpresentselecteddataelementsformthedatabase.Thiscapabilityenablesdecisionmakerstosearch,probe,andquerydatabasecontentsinordertoextractanswerstononrecurringandunplannedquesti
6、onsthataren’tavailableinregularreports.Thesequestionsmightinitiallybevagueand/orpoorlydefined,butpeoplecan“browse”throughthedatabaseuntiltheyhavetheneededinformation.Inshort,theDBMSwill“manage”thestoreddataitemsandassembletheneededitemsfromthecommondatabaseinresponsetothequeriesofthosewhoaren’tp
7、rogrammers.Adatabasemanagementsystem(DBMS)iscomposedofthreemajorparts:(1)astoragesubsystemthatstoresandretrievesdatainfiles;(2)amodelingandmanipulationsubsystemthatprovidesthemeanswithwhichtoorganizethedataandtoadd,delete,ma
