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IntroductiontoDBMSAdatabasemanagementsystem(DBMS)isanimportanttypeofprogrammingsystem,usedtodayonthebiggestandthesmallestcomputers.Asforothermajorformsofsystemsoftware,suchascompilersandoperatingsystems,awell-understoodsetofprinciplesfordatabasemanagementsystemshasdevelopedovertheyears,andtheseconceptsareusefulbothforunderstandinghowtousethesesystemseffectivelyandfordesigningandimplementingDBMS's.DBMSisacollectionofprogramsthatenablesyoutostore,modify,andextractinformationfromadatabase.TherearemanydifferenttypesofDBMS's,rangingfromsmallsystemsthatrunonpersonalcomputerstohugesystemsthatrunonmainframes.Thefollowingarethelocationofdatabasebetweenapplicationprogramsandend-users.Therearetwoqualitiesthatdistinguishdatabasemanagementsystemsfromothersortsofprogrammingsystems.1)Theabilitytomanagepersistentdata,and2)Theabilitytoaccesslargeamountsofdataefficiently.Point1)merelystatesthatthereisadatabasewhichexistspermanently;thecontentsofthisdatabaseisthedatathataDBMSaccessesandmanages.Point2)distinguishesaDBMSfromafilesystem,whichalsomanagespersistentdata.ADBMS'scapabilitiesareneededmostwhentheamountofdataisverylarge,becauseforsmallamountsofdata,simpleaccesstechniques,suchaslinearscansofthedata,areusuallyadequate.WhileweregardtheabovetwopropertiesofaDBMSasfundamental,thereareanumberofothercapabilitiesthatarealmostuniversallyfoundincommercialDBMS's.Theseare:Supportforatleastonedatamodel,ormathematicalabstractionthroughwhichtheusercanviewthedata.Supportforcertainhigh-levellanguagesthatallowtheusertodefinethestructureofdata,accessdata,andmanipulatedata.Transactionmanagement,thecapabilitytoprovidecorrect,concurrentaccesstothedatabasebymanyusersatonce.Accesscontrol,theabilitytolimitaccesstodatabyunauthorizedusers,andtheabilitytocheckthevalidityofdata.Resiliency,theabilitytorecoverfromsystemfailureswithoutlosingdata.DataModelsEachDBMSprovidesatleastoneabstractmodelofdatathatallowstheusertoseeinformationnotasrawbits,butinmoreunderstandableterms.Infact,itisusuallypossibl
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