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1、Chapter1:IntroductionChapter1:IntroductionPurposeofDatabaseSystemsViewofDataDatabaseLanguagesRelationalDatabasesDatabaseDesignObject-basedandsemistructureddatabasesDataStorageandQueryingTransactionManagementDatabaseArchitectureDatabaseUsersandAdministratorsOverallStruct
2、ureHistoryofDatabaseSystemsDatabaseManagementSystem(DBMS)DBMScontainsinformationaboutaparticularenterpriseCollectionofinterrelateddataSetofprogramstoaccessthedataAnenvironmentthatisbothconvenientandefficienttouseDatabaseApplications:Banking:alltransactionsAirlines:reser
3、vations,schedulesUniversities:registration,gradesSales:customers,products,purchasesOnlineretailers:ordertracking,customizedrecommendationsManufacturing:production,inventory,orders,supplychainHumanresources:employeerecords,salaries,taxdeductionsDatabasestouchallaspectsof
4、ourlivesPurposeofDatabaseSystemsIntheearlydays,databaseapplicationswerebuiltdirectlyontopoffilesystemsDrawbacksofusingfilesystemstostoredata:DataredundancyandinconsistencyMultiplefileformats,duplicationofinformationindifferentfilesDifficultyinaccessingdataNeedtowriteane
5、wprogramtocarryouteachnewtaskDataisolation—multiplefilesandformatsIntegrityproblemsIntegrityconstraints(e.g.accountbalance>0)become“buried”inprogramcoderatherthanbeingstatedexplicitlyHardtoaddnewconstraintsorchangeexistingonesPurposeofDatabaseSystems(Cont.)Drawbacksofus
6、ingfilesystems(cont.)AtomicityofupdatesFailuresmayleavedatabaseinaninconsistentstatewithpartialupdatescarriedoutExample:TransferoffundsfromoneaccounttoanothershouldeithercompleteornothappenatallConcurrentaccessbymultipleusersConcurrentaccessedneededforperformanceUncontr
7、olledconcurrentaccessescanleadtoinconsistenciesExample:TwopeoplereadingabalanceandupdatingitatthesametimeSecurityproblemsHardtoprovideuseraccesstosome,butnotall,dataDatabasesystemsoffersolutionstoalltheaboveproblemsLevelsofAbstractionPhysicallevel:describeshowarecord(e.
8、g.,customer)isstored.Logicallevel:describesdatastoredindatabase,andtherelationshipsamongthedata.typecustomer=r
