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.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,
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