毕业设计数据库管理外文文献Word格式文档下载.docx
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毕业设计数据库管理外文文献Word格式文档下载.docx
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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"
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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