毕业设计数据库管理外文文献.docx

毕业设计数据库管理外文文献.docx

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毕业设计数据库管理外文文献

1．Databasemanagementsystem

1.Databasemanagementsystem

ADatabaseManagementSystem（DBMS）isasetofcomputerprogramsthatcontrolsthecreation,maintenance,andtheuseofadatabase.Itallowsorganizationstoplacecontrolofdatabasedevelopmentinthehandsofdatabaseadministrators（DBAs）andotherspecialists.ADBMSisasystemsoftwarepackagethathelpstheuseofintegratedcollectionofdatarecordsandfilesknownasdatabases.Itallowsdifferentuserapplicationprogramstoeasilyaccessthesamedatabase.DBMSsmayuseanyofavarietyofdatabasemodels,suchasthenetworkmodelorrelationalmodel.Inlargesystems,aDBMSallowsusersandothersoftwaretostoreandretrievedatainastructuredway.Insteadofhavingtowritecomputerprogramstoextractinformation,usercanasksimplequestionsinaquerylanguage.Thus,manyDBMSpackagesprovideFourth-generationprogramminglanguage（4GLs）andotherapplicationdevelopmentfeatures.Ithelpstospecifythelogicalorganizationforadatabaseandaccessandusetheinformationwithinadatabase.Itprovidesfacilitiesforcontrollingdataaccess,enforcingdataintegrity,managingconcurrency,andrestoringthedatabasefrombackups.ADBMSalsoprovidestheabilitytologicallypresentdatabaseinformationtousers.

2.Overview

ADBMSisasetofsoftwareprogramsthatcontrolstheorganization,storage,management,andretrievalofdatainadatabase.DBMSsarecategorizedaccordingtotheirdatastructuresortypes.TheDBMSacceptsrequestsfordatafromanapplicationprogramandinstructstheoperatingsystemtotransfertheappropriatedata.Thequeriesandresponsesmustbesubmittedandreceivedaccordingtoaformatthatconformstooneormoreapplicableprotocols.WhenaDBMSisused,informationsystemscanbechangedmuchmoreeasilyastheorganization'sinformationrequirementschange.Newcategoriesofdatacanbeaddedtothedatabasewithoutdisruptiontotheexistingsystem.

DatabaseserversarecomputersthatholdtheactualdatabasesandrunonlytheDBMSandrelatedsoftware.Databaseserversareusuallymultiprocessorcomputers,withgenerousmemoryandRAIDdiskarraysusedforstablestorage.Hardwaredatabaseaccelerators,connectedtooneormoreserversviaahigh-speedchannel,arealsousedinlargevolumetransactionprocessingenvironments.DBMSsarefoundattheheartofmostdatabaseapplications.DBMSsmaybebuiltaroundacustommultitaskingkernelwithbuilt-innetworkingsupport,butmodernDBMSstypicallyrelyonastandardoperatingsystemtoprovidethesefunctions.

3.History

Databaseshavebeeninusesincetheearliestdaysofelectroniccomputing.Unlikemodernsystemswhichcanbeappliedtowidelydifferentdatabasesandneeds,thevastmajorityofoldersystemsweretightlylinkedtothecustomdatabasesinordertogainspeedattheexpenseofflexibility.OriginallyDBMSswerefoundonlyinlargeorganizationswiththecomputerhardwareneededtosupportlargedatasets.

3.11960sNavigationalDBMS

Ascomputersgrewinspeedandcapability,anumberofgeneral-purposedatabasesystemsemerged;bythemid-1960stherewereanumberofsuchsystemsincommercialuse.Interestinastandardbegantogrow,andCharlesBachman,authorofonesuchproduct,IntegratedDataStore（IDS）,foundedthe"DatabaseTaskGroup"withinCODASYL,thegroupresponsibleforthecreationandstandardizationofCOBOL.In1971theydeliveredtheirstandard,whichgenerallybecameknownasthe"Codasylapproach",andsoontherewereanumberofcommercialproductsbasedonitavailable.

TheCodasylapproachwasbasedonthe"manual"navigationofalinkeddatasetwhichwasformedintoalargenetwork.Whenthedatabasewasfirstopened,theprogramwashandedbackalinktothefirstrecordinthedatabase,whichalsocontainedpointerstootherpiecesofdata.Tofindanyparticularrecordtheprogrammerhadtostepthroughthesepointersoneatatimeuntiltherequiredrecordwasreturned.Simplequerieslike"findallthepeopleinIndia"requiredtheprogramtowalktheentiredatasetandcollectthematchingresults.Therewas,essentially,noconceptof"find"or"search".Thismightsoundlikeaseriouslimitationtoday,butinanerawhenthedatawasmostoftenstoredonmagnetictapesuchoperationsweretooexpensivetocontemplateanyway.

IBMalsohadtheirownDBMSsystemin1968,knownasIMS.IMSwasadevelopmentofsoftwarewrittenfortheApolloprogramontheSystem/360.IMSwasgenerallysimilarinconcepttoCodasyl,butusedastricthierarchyforitsmodelofdatanavigationinsteadofCodasyl'snetworkmodel.Bothconceptslaterbecameknownasnavigationaldatabasesduetothewaydatawasaccessed,andBachman's1973TuringAwardawardpresentationwasTheProgrammerasNavigator.IMSisclassifiedasahierarchicaldatabase.IMSandIDMS,bothCODASYLdatabases,aswellasCINCOMsTOTALdatabaseareclassifiedasnetworkdatabases.

3.21970sRelationalDBMS

EdgarCoddworkedatIBMinSanJose,California,inoneoftheiroffshootofficesthatwasprimarilyinvolvedinthedevelopmentofharddisksystems.HewasunhappywiththenavigationalmodeloftheCodasylapproach,notablythelackofa"search"facilitywhichwasbecomingincreasinglyuseful.In1970,hewroteanumberofpapersthatoutlinedanewapproachtodatabaseconstructionthateventuallyculminatedinthegroundbreakingARelationalModelofDataforLargeSharedDataBanks.[1]

Inthispaper,hedescribedanewsystemforstoringandworkingwithlargedatabases.Insteadofrecordsbeingstoredinsomesortoflinkedlistoffree-formrecordsasinCodasyl,Codd'sideawastousea"table"offixed-lengthrecords.Alinked-listsystemwouldbeveryinefficientwhenstoring"sparse"databaseswheresomeofthedataforanyonerecordcouldbeleftempty.Therelationalmodelsolvedthisbysplittingthedataintoaseriesofnormalizedtables,withoptionalelementsbeingmovedoutofthemaintabletowheretheywouldtakeuproomonlyifneeded.

Forinstance,acommonuseofadatabasesystemistotrackinformationaboutusers,theirname,logininformation,variousaddressesandphonenumbers.Inthenavigationalapproachallofthesedatawouldbeplacedinasinglerecord,andunuseditemswouldsimplynotbeplacedinthedatabase.Intherelationalapproach,thedatawouldbenormalizedintoausertable,anaddresstableandaphonenumbertable（forinstance）.Recordswouldbecreatedintheseoptionaltablesonlyiftheaddressorphonenumberswereactuallyprovided.

Linkingtheinformationbacktogetheristhekeytothissystem.Intherelationalmodel,somebitofinformationwasusedasa"key",uniquelydefiningaparticularrecord.Wheninformationwasbeingcollectedaboutauser,informationstoredintheoptional（orrelated）tableswouldbefoundbysearchingforthiskey.Forinstance,iftheloginnameofauserisunique,addressesandphonenumbersforthatuserwouldberecordedwiththeloginnameasitskey.This"re-linking"ofrelateddatabackintoasinglecollectionissomethingthattraditionalcomputerlanguagesarenotdesignedfor.

Justasthenavigationalapproachwouldrequireprogramstoloopinordertocollectrecords,therelationalapproachwouldrequireloopstocollectinformationaboutanyonerecord.Codd'ssolutiontothenecessaryloopingwasaset-orientedlanguage,asuggestionthatwouldlaterspawntheubiquitousSQL.Usingabranchofmathematicsknownastuplecalculus,hedemonstratedthatsuchasystemcouldsupportalltheoperationsofnormaldatabases（inserting,updatingetc.）aswellasprovidingasimplesystemforfindingandreturningsetsofdatainasingleoperation.

Codd'spaperwaspickedupbytwopeopleattheBerkeley,EugeneWongandMichaelStonebraker.TheystartedaprojectknownasINGRESusingfundingthathadalreadybeenallocatedforageographicaldatabaseproject,usingstudentprogrammerstoproducecode.Beginningin1973,INGRESdelivereditsfirsttestproductswhichweregenerallyreadyforwidespreadusein1979.Duringthistime,anumberofpeoplehadmoved"through"thegroup—perhapsasmanyas30peopleworkedontheproject,aboutfiveatatime.INGRESwassimilartoSystemRinanumberofways,includingtheuseofa"language"fordataaccess,knownasQUEL—QUELwasinfactrelational,havingbeenbasedonCodd'sownAlphalanguage,buthassincebeencorruptedtofollowSQL,thusviolatingmuchthesameconceptsoftherelationalmodelasSQLitself.

IBMitselfdidonetestimplementationoftherelationalmodel,PRTV,andaproductionone,BusinessSystem12,bothnowdiscontinued.HoneywelldidMRDSforMultics,andnowtherearetwonewimplementations:

AlphoraDataphorandRel.AllotherDBMSimplementationsusuallycalledrelationalareactuallySQLDBMSs.In1968,theUniversityofMichiganbegandevelopmentoftheMicroDBMSrelationaldatabasemanagementsystem.ItwasusedtomanageverylargedatasetsbytheUSDepartmentofLabor,theEnvironmentalProtectionAgencyandresearchersfromUniversityofAlberta,theUniversityofMichiganandWayneStateUniversity.ItranonmainframecomputersusingMichiganTerminalSystem.Thesystemremainedinproductionuntil1996.

3.3End1970sSQLDBMS

IBMstartedworkingonaprototypesystemlooselybasedonCodd'sconceptsasSystemRintheearly1970s.Thefirstversionwasreadyin1974/5,andworkthenstartedonmulti-tablesystemsinwhichthedatacouldbesplitsothatallofthedataforarecord（muchofwhichisoftenoptional）didnothavetobestoredinasinglelarge"chunk".Subsequentmulti-userversionsweretestedbycustomersin1978and1979,bywhichtimeastandardizedquerylanguage,