1、1本科毕业论文外文翻译外文文献原文GETTINGTOKNOWRELATIONALDATABASESMATERIALSOURCEBEGINNINGC2008DATABASES，FROMNOVICETOPROFESSIONALNOTESINAPRESSAUTHORVIDYAVRATAGARWALANDJAMESHUDDLESTONNOWTHATYOUHAVEGOTTENTOKNOWTHETOOLSYOULLUSEINTHISBOOK,WELLSTEPBACKABITTOGIVEYOUABRIEFINTRODUCTIONTOTHEIMPORTANTCONCEPTSOFTHEPCDATABASEWOR
2、LDBEFOREDIVINGINTOTHEEXAMPLESWHATISADATABASEINVERYSIMPLETERMS,ADATABASEISACOLLECTIONOFSTRUCTUREDINFORMATIONDATABASESAREDESIGNEDSPECIFICALLYTOMANAGELARGEBODIESOFINFORMATION,ANDTHEYSTOREDATAINANORGANIZEDANDSTRUCTUREDMANNERTHATMAKESITEASYFORUSERSTOMANAGEANDRETRIEVETHATDATAWHENREQUIREDADATABASEMANAGEMEN
3、TSYSTEMDBMSISASOFTWAREPROGRAMTHATENABLESUSERSTOCREATEANDMAINTAINDATABASESADBMSALSOALLOWSUSERSTOWRITEQUERIESFORANINDIVIDUALDATABASETOPERFORMREQUIREDACTIONSLIKERETRIEVINGDATA,MODIFYINGDATA,DELETINGDATA,ANDSOFORTHDBMSSSUPPORTTABLESAKARELATIONSORENTITIESTOSTOREDATAINROWSAKARECORDSORTUPLESANDCOLUMNSAKAFI
4、ELDSORATTRIBUTES,SIMILARTOHOWDATAAPPEARSINASPREADSHEETAPPLICATIONARELATIONALDATABASEMANAGEMENTSYSTEM,ORRDBMS,ISATYPEOFDBMSTHATSTORESINFORMATIONINTHEFORMOFRELATEDTABLESRDBMSISBASEDONTHERELATIONALMODELCHOOSINGBETWEENASPREADSHEETANDADATABASEIFDATABASESAREMUCHLIKESPREADSHEETS,WHYDOPEOPLESTILLUSEDATABASE
5、APPLICATIONSADATABASEISDESIGNEDTOPERFORMTHEFOLLOWINGACTIONSINANEASIERANDMOREPRODUCTIVEMANNERTHANASPREADSHEETAPPLICATIONWOULDREQUIRERETRIEVEALLRECORDSTHATMATCHPARTICULARCRITERIAUPDATEORMODIFYACOMPLETESETOFRECORDSATONETIME2EXTRACTVALUESFROMRECORDSDISTRIBUTEDAMONGMULTIPLETABLESWHYUSEADATABASEFOLLOWINGA
6、RESOMEOFTHEREASONSWEUSEDATABASESCOMPACTNESSDATABASESHELPINMAINTAININGLARGEAMOUNTSOFDATA,ANDTHUSCOMPLETELYREPLACEVOLUMINOUSPAPERFILESSPEEDSEARCHESFORAPARTICULARPIECEOFDATAORINFORMATIONINADATABASEAREMUCHFASTERTHANSORTINGTHROUGHPILESOFPAPERLESSDRUDGERYMAINTAININGFILESBYHANDISDULLWORKUSINGADATABASECOMPL
7、ETELYELIMINATESSUCHMAINTENANCECURRENCYDATABASESYSTEMSCANEASILYBEUPDATEDANDSOPROVIDEACCURATEINFORMATIONALLTHETIMEANDONDEMANDBENEFITSOFUSINGARELATIONALDATABASEMANAGEMENTSYSTEMRDBMSSOFFERVARIOUSBENEFITSBYCONTROLLINGTHEFOLLOWINGREDUNDANCYRDBMSSPREVENTHAVINGMULTIPLEDUPLICATECOPIESOFTHESAMEDATA,WHICHTAKES
8、UPDISKSPACEUNNECESSARILYINCONSISTENCYEACHREDUNDANTSETOFDATAMAYNOLONGERAGREEWITHOTHERSETSOFTHESAMEDATAWHENANRDBMSREMOVESREDUNDANCY,INCONSISTENCYCANNOTOCCURDATAINTEGRITYDATAVALUESSTOREDINTHEDATABASEMUSTSATISFYCERTAINTYPESOFCONSISTENCYCONSTRAINTSDATAATOMICITYINEVENTOFAFAILURE,DATAISRESTOREDTOTHECONSIST
9、ENTSTATEITEXISTEDINPRIORTOTHEFAILUREFOREXAMPLE,FUNDTRANSFERACTIVITYMUSTBEATOMICACCESSANOMALIESRDBMSSPREVENTMORETHANONEUSERFROMUPDATINGTHESAMEDATASIMULTANEOUSLYSUCHCONCURRENTUPDATESMAYRESULTININCONSISTENTDATADATASECURITYNOTEVERYUSEROFTHEDATABASESYSTEMSHOULDBEABLETOACCESSALLTHEDATASECURITYREFERSTOTHEP
10、ROTECTIONOFDATAAGAINSTANYUNAUTHORIZEDACCESSTRANSACTIONPROCESSINGATRANSACTIONISASEQUENCEOFDATABASEOPERATIONSTHATREPRESENTSALOGICALUNITOFWORKINRDBMSS,ATRANSACTIONEITHERCOMMITSALLTHECHANGESORROLLSBACKALLTHEACTIONSPERFORMEDUNTILTHEPOINTATWHICHFAILUREOCCURREDRECOVERYRECOVERYFEATURESENSURETHATDATAISREORGA
11、NIZEDINTOACONSISTENT3STATEAFTERATRANSACTIONFAILSSTORAGEMANAGEMENTRDBMSSPROVIDEAMECHANISMFORDATASTORAGEMANAGEMENTTHEINTERNALSCHEMADEFINESHOWDATASHOULDBESTOREDCOMPARINGDESKTOPANDSERVERRDBMSSYSTEMSINTHEINDUSTRYTODAY,WEMAINLYWORKWITHTWOTYPESOFDATABASESDESKTOPDATABASESANDSERVERDATABASESHERE,WELLGIVEYOUAB
12、RIEFLOOKATEACHOFTHEMDESKTOPDATABASESDESKTOPDATABASESAREDESIGNEDTOSERVEALIMITEDNUMBEROFUSERSANDRUNONDESKTOPPCS,ANDTHEYOFFERALESSEXPENSIVESOLUTIONWHEREVERADATABASEISREQUIREDCHANCESAREYOUHAVEWORKEDWITHADESKTOPDATABASEPROGRAMMICROSOFTSQLSERVEREXPRESS,MICROSOFTACCESS,MICROSOFTFOXPRO,FILEMAKERPRO,PARADOX,
13、ANDLOTUSREPRESENTAWIDERANGEOFDESKTOPDATABASESOLUTIONSDESKTOPDATABASESDIFFERFROMSERVERDATABASESINTHEFOLLOWINGWAYSLESSEXPENSIVEMOSTDESKTOPSOLUTIONSAREAVAILABLEFORJUSTAFEWHUNDREDDOLLARSINFACT,IFYOUOWNALICENSEDVERSIONOFMICROSOFTOFFICEPROFESSIONAL,YOUREALREADYALICENSEDOWNEROFMICROSOFTACCESS,WHICHISONEOFT
14、HEMOSTCOMMONLYANDWIDELYUSEDDESKTOPDATABASEPROGRAMSAROUNDUSERFRIENDLYDESKTOPDATABASESAREQUITEUSERFRIENDLYANDEASYTOWORKWITH,ASTHEYDONOTREQUIRECOMPLEXSQLQUERIESTOPERFORMDATABASEOPERATIONSALTHOUGHSOMEDESKTOPDATABASESALSOSUPPORTSQLSYNTAXIFYOUWOULDLIKETOCODEDESKTOPDATABASESGENERALLYOFFERANEASYTOUSEGRAPHIC
15、ALUSERINTERFACESERVERDATABASESSERVERDATABASESARESPECIFICALLYDESIGNEDTOSERVEMULTIPLEUSERSATATIMEANDOFFERFEATURESTHATALLOWYOUTOMANAGELARGEAMOUNTSOFDATAVERYEFFICIENTLYBYSERVINGMULTIPLEUSERREQUESTSSIMULTANEOUSLYWELLKNOWNEXAMPLESOFSERVERDATABASESINCLUDEMICROSOFTSQLSERVER,ORACLE,SYBASE,ANDDB2HEREARESOMEOT
16、HERCHARACTERISTICSTHATDIFFERENTIATESERVERDATABASESFROMTHEIRDESKTOPCOUNTERPARTSFLEXIBILITYSERVERDATABASESAREDESIGNEDTOBEVERYFLEXIBLETOSUPPORTMULTIPLEPLATFORMS,RESPONDTOREQUESTSCOMINGFROMMULTIPLEDATABASEUSERS,AND4PERFORMANYDATABASEMANAGEMENTTASKWITHOPTIMUMSPEEDAVAILABILITYSERVERDATABASESAREINTENDEDFOR
17、ENTERPRISES,ANDSOTHEYNEEDTOBEAVAILABLE24/7TOBEAVAILABLEALLTHETIME,SERVERDATABASESCOMEWITHSOMEHIGHAVAILABILITYFEATURES,SUCHASMIRRORINGANDLOGSHIPPINGPERFORMANCESERVERDATABASESUSUALLYHAVEHUGEHARDWARESUPPORT,ANDSOSERVERSRUNNINGTHESEDATABASESHAVELARGEAMOUNTSOFRAMANDMULTIPLECPUS,ANDTHISISWHYSERVERDATABASE
18、SSUPPORTRICHINFRASTRUCTUREANDGIVEOPTIMUMPERFORMANCESCALABILITYTHISPROPERTYALLOWSASERVERDATABASETOEXPANDITSABILITYTOPROCESSANDSTORERECORDSEVENIFITHASGROWNTREMENDOUSLYTHEDATABASELIFECYCLETHEDATABASELIFECYCLEDEFINESTHECOMPLETEPROCESSFROMCONCEPTIONTOIMPLEMENTATIONTHEENTIREDEVELOPMENTANDIMPLEMENTATIONPRO
19、CESSOFTHISCYCLECANBEDIVIDEDINTOSMALLPHASESONLYAFTERTHECOMPLETIONOFEACHPHASECANYOUMOVEONTOTHENEXTPHASE,ANDTHISISTHEWAYYOUBUILDYOURDATABASEBLOCKBYBLOCKBEFOREGETTINGINTOTHEDEVELOPMENTOFANYSYSTEM,YOUNEEDTOHAVESTRONGALIFECYCLEMODELTOFOLLOWTHEMODELMUSTHAVEALLTHEPHASESDEFINEDINPROPERSEQUENCE,WHICHWILLHELPT
20、HEDEVELOPMENTTEAMTOBUILDTHESYSTEMWITHFEWERPROBLEMSANDFULLFUNCTIONALITYASEXPECTEDTHEDATABASELIFECYCLECONSISTSOFTHEFOLLOWINGSTAGES,FROMTHEBASICSTEPSINVOLVEDINDESIGNINGAGLOBALSCHEMAOFTHEDATABASETODATABASEIMPLEMENTATIONANDMAINTENANCEREQUIREMENTANALYSISREQUIREMENTSNEEDTOBEDETERMINEDBEFOREYOUCANBEGINDESIG
21、NANDIMPLEMENTATIONTHEREQUIREMENTSCANBEGATHEREDBYINTERVIEWINGBOTHTHEPRODUCERANDTHEUSEROFTHEDATATHISPROCESSHELPSINCREATINGAFORMALREQUIREMENTSPECIFICATIONLOGICALDESIGNAFTERREQUIREMENTGATHERING,DATAANDRELATIONSHIPSNEEDTOBEDEFINEDUSINGACONCEPTUALDATAMODELINGTECHNIQUESUCHASANENTITYRELATIONSHIPERDIAGRAMPHY
22、SICALDESIGNONCETHELOGICALDESIGNISINPLACE,THENEXTSTEPISTOPRODUCE5THEPHYSICALSTRUCTUREFORTHEDATABASETHEPHYSICALDESIGNPHASEINVOLVESTABLECREATIONANDSELECTIONOFINDEXESDATABASEIMPLEMENTATIONONCETHEDESIGNISCOMPLETED,THEDATABASECANBECREATEDTHROUGHIMPLEMENTATIONOFFORMALSCHEMAUSINGTHEDATADEFINITIONLANGUAGEDDL
23、OFTHERDBMSDATAMODIFICATIONDATAMODIFICATIONLANGUAGEDMLCANBEUSEDTOQUERYANDUPDATETHEDATABASEASWELLASSETUPINDEXESANDESTABLISHCONSTRAINTSSUCHASREFERENTIALINTEGRITYDATABASEMONITORINGASTHEDATABASEBEGINSOPERATION,MONITORINGINDICATESWHETHERPERFORMANCEREQUIREMENTSAREBEINGMETIFTHEYARENOT,MODIFICATIONSSHOULDBEM
24、ADETOIMPROVEDATABASEPERFORMANCETHUSTHEDATABASELIFECYCLECONTINUESWITHMONITORING,REDESIGN,ANDMODIFICATIONMAPPINGCARDINALITIESTABLESARETHEFUNDAMENTALCOMPONENTSOFARELATIONALDATABASEINFACT,BOTHDATAANDRELATIONSHIPSARESTOREDSIMPLYASDATAINTABLESTABLESARECOMPOSEDOFROWSANDCOLUMNSEACHCOLUMNREPRESENTSAPIECEOFIN
25、FORMATIONMAPPINGCARDINALITIES,ORCARDINALITYRATIOS,EXPRESSTHENUMBEROFENTITIESTOWHICHANOTHERENTITYCANBEASSOCIATEDVIAARELATIONSHIPSETCARDINALITYREFERSTOTHEUNIQUENESSOFDATAVALUESCONTAINEDINAPARTICULARCOLUMNOFADATABASETABLETHETERMRELATIONALDATABASEREFERSTOTHEFACTTHATDIFFERENTTABLESQUITEOFTENCONTAINRELATE
26、DDATAFOREXAMPLE,ONESALESREPINACOMPANYMAYTAKEMANYORDERS,WHICHWEREPLACEDBYMANYCUSTOMERSTHEPRODUCTSORDEREDMAYCOMEFROMDIFFERENTSUPPLIERS,ANDCHANCESARETHATEACHSUPPLIERCANSUPPLYMORETHANONEPRODUCTALLOFTHESERELATIONSHIPSEXISTINALMOSTEVERYDATABASEANDCANBECLASSIFIEDASFOLLOWSONETOONE11FOREACHROWINTABLEA,THEREI
27、SATMOSTONLYONERELATEDROWINTABLEB,ANDVICEVERSATHISRELATIONSHIPISTYPICALLYUSEDTOSEPARATEDATABYFREQUENCYOFUSETOOPTIMALLYORGANIZEDATAPHYSICALLYFOREXAMPLE,ONEDEPARTMENTCANHAVEONLYONEDEPARTMENTHEADONETOMANY1MFOREACHROWINTABLEA,THERECANBEZEROORMORERELATED6ROWSINTABLEB,BUTFOREACHROWINTABLEB,THEREISATMOSTONE
28、ROWINTABLEATHISISTHEMOSTCOMMONRELATIONSHIPANEXAMPLEOFAONETOMANYRELATIONSHIPOFTABLESINNORTHWINDISSHOWNINFIGURE31NOTETHECUSTOMERSTABLEHASACUSTOMERIDFIELDASTHEPRIMARYKEYINDICATEDBYTHEKEYSYMBOLONTHELEFT,WHICHHASARELATIONWITHTHECUSTOMERIDFIELDOFTHEORDERSTABLECUSTOMERIDISCONSIDEREDAFOREIGNKEYINTHEORDERSTA
29、BLETHELINKSHOWNBETWEENTHECUSTOMERSANDORDERSTABLESINDICATESAONETOMANYRELATIONSHIP,ASMANYORDERSCANBELONGTOONECUSTOMERHERE,CUSTOMERSISREFERREDTOASTHEPARENTTABLE,ANDORDERSISTHECHILDTABLEINTHERELATIONSHIPMANYTOMANYMMFOREACHROWINTABLEA,THEREAREZEROORMORERELATEDROWSINTABLEB,ANDVICEVERSAMANYTOMANYRELATIONSH
30、IPSARENOTSOEASYTOACHIEVE,7ANDTHEYREQUIREASPECIALTECHNIQUETOIMPLEMENTTHEMTHISRELATIONSHIPISACTUALLYIMPLEMENTEDINAONEMANYONEFORMAT,SOITREQUIRESATHIRDTABLEOFTENREFERREDTOASAJUNCTIONTABLETOBEINTRODUCEDINBETWEENTHATSERVESASTHEPATHBETWEENTHERELATEDTABLESTHISISAVERYCOMMONRELATIONSHIPANEXAMPLEFROMNORTHWINDI
31、SSHOWNINFIGURE32ANORDERCANHAVEMANYPRODUCTSANDAPRODUCTCANBELONGTOMANYORDERSTHEORDERDETAILSTABLENOTONLYREPRESENTSTHEMMRELATIONSHIP,BUTALSOCONTAINSDATAABOUTEACHPARTICULARORDERPRODUCTCOMBINATIONNOTETHOUGHRELATIONSHIPSAMONGTABLESAREEXTREMELYIMPORTANT,THETERMRELATIONALDATABASEHASNOTHINGTODOWITHTHEMRELATIO
32、NALDATABASESARETOVARYINGEXTENTSBASEDONTHERELATIONALMODELOFDATAINVENTEDBYDREDGARFCODDATIBMINTHE81970SCODDBASEDHISMODELONTHEMATHEMATICALSETTHEORETICCONCEPTOFARELATIONRELATIONSARESETSOFTUPLESTHATCANBEMANIPULATEDWITHAWELLDEFINEDANDWELLBEHAVEDSETOFMATHEMATICALOPERATIONSINFACT,TWOSETSRELATIONALALGEBRAANDR
33、ELATIONALCALCULUSYOUDONTHAVETOKNOWORUNDERSTANDTHEMATHEMATICSTOWORKWITHRELATIONALDATABASES,BUTIFYOUHEARITSAIDTHATADATABASEISRELATIONALBECAUSEIT“RELATESDATA,”YOULLKNOWTHATWHOEVERSAIDITDOESNTUNDERSTANDRELATIONALDATABASESUNDERSTANDINGKEYSTHEKEY,THEWHOLEKEY,ANDNOTHINGBUTTHEKEY,SOHELPMECODDRELATIONSHIPSAR
34、EREPRESENTEDBYDATAINTABLESTOESTABLISHARELATIONSHIPBETWEENTWOTABLES,YOUNEEDTOHAVEDATAINONETABLETHATENABLESYOUTOFINDRELATEDROWSINANOTHERTABLETHATSWHEREKEYSCOMEIN,ANDRDBMSSMAINLYWORKWITHTWOTYPESOFKEYS,ASMENTIONEDEARLIERPRIMARYKEYSANDFOREIGNKEYSAKEYISONEORMORECOLUMNSOFARELATIONTHATISUSEDTOIDENTIFYAROWPR
35、IMARYKEYSAPRIMARYKEYISANATTRIBUTECOLUMNORCOMBINATIONOFATTRIBUTESCOLUMNSWHOSEVALUESUNIQUELYIDENTIFYRECORDSINANENTITYBEFOREYOUCHOOSEAPRIMARYKEYFORANENTITY,ANATTRIBUTEMUSTHAVETHEFOLLOWINGPROPERTIESEACHRECORDOFTHEENTITYMUSTHAVEANOTNULLVALUETHEVALUEMUSTBEUNIQUEFOREACHRECORDENTEREDINTOTHEENTITYTHEVALUESMU
36、STNOTCHANGEORBECOMENULLDURINGTHELIFEOFEACHENTITYINSTANCETHERECANBEONLYONEPRIMARYKEYDEFINEDFORANENTITYBESIDESHELPINGINUNIQUELYIDENTIFYINGARECORD,THEPRIMARYKEYALSOHELPSINSEARCHINGRECORDSASANINDEXAUTOMATICALLYGETSGENERATEDASYOUASSIGNAPRIMARYKEYTOANATTRIBUTEANENTITYWILLHAVEMORETHANONEATTRIBUTETHATCANSER
37、VEASAPRIMARYKEYANYKEYORMINIMUMSETOFKEYSTHATCOULDBEAPRIMARYKEYISCALLEDACANDIDATEKEYONCECANDIDATEKEYSAREIDENTIFIED,CHOOSEONE,ANDONLYONE,PRIMARYKEYFOREACHENTITYSOMETIMESITREQUIRESMORETHANONEATTRIBUTETOUNIQUELYIDENTIFYANENTITYAPRIMARYKEYTHATCONSISTSOFMORETHANONEATTRIBUTEISKNOWNASACOMPOSITEKEYTHERE9CANBE
38、ONLYONEPRIMARYKEYINANENTITY,BUTACOMPOSITEKEYCANHAVEMULTIPLEATTRIBUTESIE,APRIMARYKEYWILLBEDEFINEDONLYONCE,BUTITCANHAVEUPTO16ATTRIBUTESTHEPRIMARYKEYREPRESENTSTHEPARENTENTITYPRIMARYKEYSAREUSUALLYDEFINEDWITHTHEIDENTITYPROPERTY,WHICHALLOWSINSERTIONOFANAUTOINCREMENTEDINTEGERVALUEINTOTHETABLEWHENYOUINSERTA
39、ROWINTOTHETABLEFOREIGNKEYSAFOREIGNKEYISANATTRIBUTETHATCOMPLETESARELATIONSHIPBYIDENTIFYINGTHEPARENTENTITYFOREIGNKEYSPROVIDEAMETHODFORMAINTAININGINTEGRITYINTHEDATACALLEDREFERENTIALINTEGRITYANDFORNAVIGATINGBETWEENDIFFERENTINSTANCESOFANENTITYEVERYRELATIONSHIPINTHEMODELMUSTBESUPPORTEDBYAFOREIGNKEYFOREXAM
40、PLE,INFIGURE31EARLIER,THECUSTOMERSANDORDERSTABLESHAVEAPRIMARYKEYANDFOREIGNKEYRELATIONSHIP,WHERETHEORDERSTABLESCUSTOMERIDFIELDISTHEFOREIGNKEYHAVINGAREFERENCETOTHECUSTOMERIDFIELD,WHICHISTHEPRIMARYKEYOFTHECUSTOMERSTABLEUNDERSTANDINGDATAINTEGRITYDATAINTEGRITYMEANSTHATDATAVALUESINADATABASEARECORRECTANDCO
41、NSISTENTTHEREARETWOASPECTSTODATAINTEGRITYENTITYINTEGRITYANDREFERENTIALINTEGRITYENTITYINTEGRITYWEMENTIONEDPREVIOUSLYIN“PRIMARYKEYS”THATNOPARTOFAPRIMARYKEYCANBENULLTHISISTOGUARANTEETHATPRIMARYKEYVALUESEXISTFORALLROWSTHEREQUIREMENTTHATPRIMARYKEYVALUESEXISTANDTHATTHEYAREUNIQUEISKNOWNASENTITYINTEGRITYEIT
42、HEDBMSENFORCESENTITYINTEGRITYBYNOTALLOWINGOPERATIONSINSERT,UPDATETOPRODUCEANINVALIDPRIMARYKEYANYOPERATIONTHATCREATESADUPLICATEPRIMARYKEYORONECONTAININGNULLSISREJECTEDTHATIS,TOESTABLISHENTITYINTEGRITY,YOUNEEDTODEFINEPRIMARYKEYSSOTHEDBMSCANENFORCETHEIRUNIQUENESSREFERENTIALINTEGRITYONCEARELATIONSHIPISD
43、EFINEDBETWEENTABLESWITHFOREIGNKEYS,THEKEYDATAMUSTBEMANAGEDTOMAINTAINTHECORRECTRELATIONSHIPS,THATIS,TOENFORCEREFERENTIALINTEGRITYRIRIREQUIRESTHATALLFOREIGNKEYVALUESINACHILDTABLEEITHERMATCHPRIMARYKEYVALUESINAPARENTTABLEORIFPERMITTEDBENULLTHISISALSOKNOWNASSATISFYINGAFOREIGNKEYCONSTRAINT10NORMALIZATIONC
44、ONCEPTSNORMALIZATIONISATECHNIQUEFORAVOIDINGPOTENTIALUPDATEANOMALIES,BASICALLYBYMINIMIZINGREDUNDANTDATAINALOGICALDATABASEDESIGNNORMALIZEDDESIGNSAREINASENSE“BETTER”DESIGNSBECAUSETHEYIDEALLYKEEPEACHDATAITEMINONLYONEPLACENORMALIZEDDATABASEDESIGNSUSUALLYREDUCEUPDATEPROCESSINGCOSTSBUTCANMAKEQUERYPROCESSIN
45、GMORECOMPLICATEDTHESETRADEOFFSMUSTBECAREFULLYEVALUATEDINTERMSOFTHEREQUIREDPERFORMANCEPROFILEOFADATABASEOFTEN,ADATABASEDESIGNNEEDSTOBEDENORMALIZEDTOADEQUATELYMEETOPERATIONALNEEDSNORMALIZINGALOGICALDATABASEDESIGNINVOLVESASETOFFORMALPROCESSESTOSEPARATETHEDATAINTOMULTIPLE,RELATEDTABLESTHERESULTOFEACHPRO
46、CESSISREFERREDTOASANORMALFORMFIVENORMALFORMSHAVEBEENIDENTIFIEDINTHEORY,BUTMOSTOFTHETIMETHIRDNORMALFORM3NFISASFARASYOUNEEDTOGOINPRACTICETOBEIN3NF,ARELATIONTHEFORMALTERMFORWHATSQLCALLSATABLEANDTHEPRECISECONCEPTONWHICHTHEMATHEMATICALTHEORYOFNORMALIZATIONRESTSMUSTALREADYBEINSECONDNORMALFORM2NF,AND2NFREQ
47、UIRESARELATIONTOBEINFIRSTNORMALFORM1NFLETSLOOKBRIEFLYATWHATTHESENORMALFORMSMEANFIRSTNORMALFORM1NFINFIRSTNORMALFORM,ALLCOLUMNVALUESARESCALARINOTHERWORDS,THEYHAVEASINGLEVALUETHATCANTBEFURTHERDECOMPOSEDINTERMSOFTHEDATAMODELFOREXAMPLE,ALTHOUGHINDIVIDUALCHARACTERSOFASTRINGCANBEACCESSEDTHROUGHAPROCEDURETH
48、ATDECOMPOSESTHESTRING,ONLYTHEFULLSTRINGISACCESSIBLEBYNAMEINSQL,SO,ASFARASTHEDATAMODELISCONCERNED,THEYARENTPARTOFTHEMODELLIKEWISE,FORAMANAGERSTABLEWITHAMANAGERCOLUMNANDACOLUMNCONTAININGALISTOFEMPLOYEESINEMPLOYEESTABLEWHOWORKFORAGIVENMANAGER,THEMANAGERANDTHELISTWOULDBEACCESSIBLEBYNAME,BUTTHEINDIVIDUAL
49、EMPLOYEESINTHELISTWOULDNTBEALLRELATIONSANDSQLTABLESAREBYDEFINITIONIN1NFSINCETHELOWESTLEVELOFACCESSIBILITYKNOWNASTHETABLESGRANULARITYISTHECOLUMNLEVEL,ANDCOLUMNVALUESARESCALARSINSQLSECONDNORMALFORM2NFSECONDNORMALFORMREQUIRESTHATATTRIBUTESTHEFORMALTERMFORSQLCOLUMNSTHATARENTPARTSOFKEYSBEFUNCTIONALLYDEPENDENTONAKEYTHATUNIQUELYIDENTIFIESTHEMFUNCTIONALDEPENDENCEBASICALLYMEANSTHATFORAGIVENKEY11VALUE,ONLYONEVALUEEXISTSINATABLEFORACOLUMNORSETOFCOLUMNSFOREXAMPLE,IFATABLECONTAINEDEMPLOYEESANDTHEIRTITLES,ANDMORETHANONEEMPLOYEECOULDHAVETHESAMETITLEVERYLIKELY,AKEYTHATUNIQUELYIDENTIFIEDEMPLOYE
