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1、（2009届毕业设计）外文翻译原文及译文学院（部）：计算机与通信学院专业：计算机科学与技术学生姓名：许淦班级：计052学号0540810215指导教师姓名：李建设职称副教授2009年4月湖南工业大学本科毕业设计（外文翻译原文及译文）TheSemanticWeb:AnOverviewDataIndependenceAnimportantpointaboutdatabasesystemsisthatthedatabaseshouldexistindependentlyofanyofthespecific

2、applications.Traditionaldataprocessingapplicationsaredatadependent.COBOLprogramscontainfiledescriptionsandrecorddescriptionsthatcarefullydescribetheformatandcharacteristicsofthedata.Usersshouldbeabletochangethestructureofthedatabasewithoutaffectingthea

3、pplicationsthatuseit.Forexample,supposethattherequirementsofyourapplicationschange.AsimpleexamplewouldbeexpandingZIPcodesfromfivedigitstoninedigits.OnatraditionalapproachusingCOBOLprogramseachindividualCOBOLapplicationprogramthatusedthatparticularfield

4、wouldhavetobechanged,recompiled,andretested.Theprogramswouldbeunabletorecognizeoraccessafilethathadbeenchangedandcontainedanewdatadescription;this,inturn,mightcausedisruptioninprocessingunlessthechangewerecarefullyplanned.Mostdatabaseprogramsprovidethe

5、abilitytochangethedatabasestructurebysimplychangingtheZIPcodefieldandthedata-entryform.Inthiscase,dataindependenceallowsforminimaldisruptionofcurrentandexistingapplications.Userscancontinuetoworkandcanevenignorethenine-digitcodeiftheychoose.Eventually,

6、thefilewillbeconvertedtothenewnine-digitZIPcode,buttheeasewithwhichthechangeovertakesplaceemphasizestheimportanceofdataindependence.DataIntegrityDataintegrityreferstotheaccuracy,correctness,orvalidityofthedatainthedatabase.Inadatabasesystem,dataintegri

7、tymeanssafeguardingthedataagainstinvalidalterationordestructionarise.Thefirsthastodowithmanyusersaccessingthedatabaseconcurrently.Forexample,ifthousandsoftravelagentsandairlinereservationclerksareaccessingthedatabaseconcurrently.Forexample,ifthousandso

8、ftravelagentsandairlinereservationclerksareaccessingthesamedatabaseatonce,andtwoagentsbookthesameseatonthesameflight,thefirstagent’sbookingwillbelost.Insuchcasethetechniqueoflockingtherecordorfieldprovidesthemeansforpreventingoneuserfro