数据库作业答案-ch.ppt

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1、Chapter1:IntroductionPurposeofDatabaseSystemsViewofDataDataModelsDataDefinitionLanguageDataManipulationLanguageTransactionManagementStorageManagementDatabaseAdministratorDatabaseUsersOverallSystemStructure1.1DatabaseSystemApplicationsDatabaseSystemCollectionofinterrelateddataAdatabasecontainsin

2、formationaboutaparticularenterpriseSetofprogramstoaccessthedataDBMSprovidesanenvironmentthatisbothconvenientandefficienttouse.DatabaseApplications:Banking:alltransactionsAirlines:reservations,schedulesUniversities:registration,gradesSales:customers,products,purchasesManufacturing:production,inv

3、entory,orders,supplychainHumanresources:employeerecords,salaries,taxdeductionsDatabasestouchallaspectsofourlives1.2DatabaseSystemsversusFileSystemsPurposeofDatabaseSystemIntheearlydays,databaseapplicationswerebuiltontopoffilesystemsDrawbacksofusingfilesystemstostoredata:Dataredundancyandincons

4、istencyMultiplefileformats,duplicationofinformationindifferentfilesDifficultyinaccessingdataNeedtowriteanewprogramtocarryouteachnewtaskDataisolation—multiplefilesandformatsIntegrityproblemsIntegrityconstraints(e.g.accountbalance>0)becomepartofprogramcodeHardtoaddnewconstraintsorchangeexistingon

5、esPurposeofDatabaseSystems(Cont.)Drawbacksofusingfilesystems(cont.)AtomicityofupdatesFailuresmayleavedatabaseinaninconsistentstatewithpartialupdatescarriedoutE.g.transferoffundsfromoneaccounttoanothershouldeithercompleteornothappenatallConcurrentaccessbymultipleusersConcurrentaccessedneededforp

6、erformanceUncontrolledconcurrentaccessescanleadtoinconsistenciesE.g.twopeoplereadingabalanceandupdatingitatthesametimeSecurityproblemsDatabasesystemsoffersolutionstoalltheaboveproblems1.3ViewofDataLevelsofAbstractionPhysicalleveldescribeshowarecord(e.g.,customer)isstored.Logicalleveldescribesda

7、tastoredindatabase,andtherelationshipsamongthedata.typecustomer=recordname:string;street:string;city:integer;end;PhysicalDataIndependence–theabilitytomodifythephysicalschemawithoutchangingthelogicalschemaApplicationsdependonthel