c語言基本知識（BasicknowledgeofClanguage）

c語言基本知識(BasicknowledgeofClanguage)SummarizethetwobasicknowledgeofthepubliccomputerSummarizethetwobasicknowledgeofthepubliccomputerThefirstchapter,datastructureandalgorithmThe1.1algorithmThesolutionalgorithmisaccurateandcompletedescription.Thebasiccharacteristicsofthealgorithmareasetofcarefullydefinedsequenceofoperationrules,eachruleiseffective,Isclear,thisorderwillterminateinalimitednumberof.Featuresinclude:Thealgorithmisnotequaltotheprogram,norcomputerprogrammingmethod,thealgorithmdesignisbetterthannotpossible.thefeasibility;uncertainty,eachstepinthealgorithmhastobeclearlydefined,notallowedtohavereadytoaccepteithercourseexplanation,Thereisambiguityisnotallowed;thereispoor,thealgorithmmustbedonewithinalimitedperiodoftime,whichcanterminateintheimplementationoffinitesteps,includingreasonableexecutiontimemeaning;havesufficientinformation.Thebasicelementsofthealgorithm:oneistheoperationandoperationofdataobjects;twoistocontrolthestructureofthealgorithm.Instructionsystem:setalltheinstructionsofacomputersystemcanbeexecuted.Thebasicoperationandoperationincluding:arithmeticlogic,relationaloperationanddatatransmission.Thetimecomplexityofthealgorithmistoexecutetheworkloadneededbythealgorithm.Thebasicdesignmethod:enumerationmethod,inductivemethod,recursive,recursiveandrecursivereductionbuckettechnology,backtracking.Thecomplexityofthealgorithm:thealgorithmoftimecomplexityandspacecomplexityofthealgorithm.Thecontrolstructureofthealgorithm:sequencestructure,selectionofstructure,circulationstructure.Thespacecomplexityofthealgorithmisthatthealgorithmperformstherequiredmemoryspace.2basicconceptofdatastructureThreeaspectsofdatastructure:thelogicalrelationshipbetweeneachdatasetinthedataelementsinherentinthedatalogicalstructure;inthedataprocessing,thedataelementsstoredinthecomputerdatastorageStructure;ontheoperationofthedatastructure.Thedatastructureisacollectionofdataelementsthatarerelatedtoeachother.Containsthelogicstructureofdata:saiddataelementinformation;beforeandafterthesaiddataelementsoftherelationshipbetween.Thedatastoragestructureinorder,linkandindex.Linearstructure:thereisonlyonerootnode;eachnodehasatmostonebefore,alsohasatmostonepieceafter.Nonlinearstructure:thedatastructureofthelinearstructuredoesnotmeettheconditions.1.3lineartableandsequentialstoragestructureThelineartableconsistsofasetofdataelements,dataelementsonlydependsonthelocationoftheirnumber,betweenelementsTherelativepositionislinear.Inthecomplexlineartable,thedataelementiscomposedofapluralityofdataelementscalledrecords,andmultiplerecords.Alineartableiscalledafile.Thestructurecharacteristicsofnonempty1ineartable:onlyonerootnodeAl,itnoonebefore;thereisonlyoneterminalnodean,itisnota;therootnodeandterminalnode,allothernodesandthereisonlyonethingbefore,alsohasonlyoneAfterapieceof.Thenumberofnodesinniscalledthelinearlengthofthetable,whenn=0,Calledtheemptytable.Theorderofthelineartablestoragestructurehasthefollowingtwobasiccharacteristics:forthestoragespaceofallelementsinalinearformiscontinuous;thelineardataelementsinthetableislogicallyorderlyinthestoragespace.StorageaddressAI:ADR(AI)-ADR(Al)+(i-1)k,ADR(Al)istheaddressofthefirstelement,KEachelementrepresentsthenumberofbytesfor.Theorderofthetable:insert,deleteoperation,(see16)Stackandqueue1.4Thestackisdefinedtoinsertanddeletethelineartableatoneend,oneendtoallowinsertionanddeletioniscalledthetopofthestack,notAllowtheinsertionanddeletionoftheotherendiscalledthebottomofthestack.Thestackinaccordancewiththe"advancedafter"(FILO)or"LIFO”(LIFO)organizesthedatastackwithmemoryUse.Topsaidthetopofthestack,bottomstack.Thebasicoperationofthestack:(1)insertelementscalledstackoperations;(2)deleteelementscalledbackstackoperations(;3)readthetopelementonthestackisthetopelementassignedtoaspecifiedvariable,pointernochange.Thequeueistoallowatoneend(tail)insertedinto,andattheotherend(teamhead)ofthelineartabletodelete.Rearpointertofrontpointertothetail,headofline.Thequeueis"advancedline"(FIFO)or"LIFO"(LILO)ofthelineartable.Thequeueoperationsinclude(1)enqueueoperations:insertanelementfromtheendofthe1ine;(2)theteambackfromtheteamheadtodeleteoperations:Inadditiontoanelement.Circularqueue:s=0s=lfront=rearsaidthequeueisempty,andthatthequeueisfulllinearlistThedatastructureofeachnodecorrespondstoastorageunit,thestorageunitiscalledastoragenode,JaneCallnode.Thenodeconsistsoftwoparts:(1)forstoringdataelementvalue,calledthedatadomain;(2)forstoringmeansTheneedle,calledthepointerpointstoanodeforabeforeorafter.Inthelinkedstoragestructure,storagespacetostorethedatastructurecanbediscontinuous,thedatastoragenodeThelogicalrelationshipbetweenorderanddataelementscanbeinconsistent,andlogicalrelationshipsbetweendataelementsbywhichisTodeterminetheneedledomain.Youcanchainstorageforlinearstructure,canalsobeusedfortherepresentationofnonlinearstructure.Linearlist,HEADiscalledtheheadpointer,HEAD=NULL(or0)iscalledtheemptytable,ifitistwopointer:leftfingerTheneedle(Llink)toanode,therightpointer(RIink)toanode.Thebasicoperationoflinearlist:search,insertanddelete.treesandtwoforktreeThetreeisasimplenonlinearstructure,hastheobviouscharacteristicsoftheelementsbetweenalllevels.Inthetreestructure,eachnodehasonlyonebefore,calledaparentnode,thenodenotonlyoneTherootnodeisatree,said,referredtoastherootofthetree.Eachnodecanhavemultipleconsequents,calledthesubnodeNode.Notafterthepieceiscalledaleafnode.Inthetreestructure,anodehasanumbercalledafterthenodedegree,thelargestofallthenodesintheIscalledthetreeof.Themaximumlevelofthetreecalledthetreedepth.Thecharacteristicsofthetwoforktree:(1)twononemptybinarytreehasonlyonerootnode;(2)eachnodehasatmosttwotreesAndarecalledthesubtreeofthenodeleftsubtreeandtherightsubtree.Thebasicpropertiesofthetwoforktree:intheklayerofthetwoforktree,upto2k-1(k=1)nodes;mindepthtwotreeatmost2m-1nodes;of0nodes(i.e.,leafnodes)isalwayslessthan2degreesofanode;withnnodesoftwobinarytree,thedepthofatleast[log2n]+l,wherein[log2n]representslog2nTheintegerpart;totallytwobinarytreewithnnodesinthedepthof[log2n]+l;acompletebinarytreeoftwototalNnodes.Ifyoustartfromtherootnode,accordingtosequence(eachlayerfromlefttorightWiththenaturalnumber1,2),....ntothenodenumber(k=l,2....n),withthefollowingconclusions:Ifk=I,thenthenodeistherootnode,whichhasnoparentnode;ifk>listheparentofthenodetonodenumberINT(k/2);If2K=n,thenumberofleftsubnodeK,nodenumberis2K;otherwisetheleftchildnode(alsoNorightchild);If2k+l=n,thenumberofKnodesoftherightchildnodenumberis2k+l;otherwisethenodehasnorightchiIdWiththetwoforktreereferstotheadditionofthelastlayer,allthenodesoneachlayerhastwosubnode,a2Kklayer-1nodesinadepthofmoverthetwoforktreewith2m-1nodes.Totallytwoforktreeisdefinedinthelastlayer,thenumberofnodesoneachlevelarereachedthemaximumvalueinthelastlayer.Somenodesonlythelackofright.Twobinarytreestoragestructureusingchainstoragestructure,forthefulltwotreeandtotallytwotreeaccordingtosequenceSequentialstorage.Twobinarytreetraversal:beforethetraversal(DLR),thefirstaccessnode,andthentraversetheleftsubtree,rightsubtreetraversalfinally;inordertraversal(LDR),thefirsttraversaloftheleftsubtree,andthenvisittherootnode,andfinallytherightsubtreetraversal;afterthetraversal(LRD)firsttraversaloftheleftsubtree,andthentherightsubtreetraversal,lastaccessnode1.7searchtechnologyTheuseofasequentialsearch:lineartableasanunorderedlist;thestructureofchainstore.Anorderedlistofbinarysearchisonlyapplicabletosequentialstorage,forthelengthoflinearn,theworstcaseOnlylog2ntimes.8sequencingtechnologySortingreferstoanunorderedsequencearrangedaccordingtothevalueofnondecreasingorderedsequenceorder.Exchangesortmethod:(1)bubblesortmethod,comparingtimesforn(n-l)/2;(2)quicksortMethod.Insertionsortmethod:(1)asimpleinsertionsortmethod,theworstcaseneedsn(n-1)/2(2)andcomparison;Sortmethod,theworstcaseneeds0(nl.5)time.Selectthesortmethod:(1)simpleselectionsort,Theworstcaseneedsn(n-l)/2;(2)theheapsort,theworstcaseneeds0(nlog2n)timeThesecondchapterprogramdesign1programdesignmethodanddesignstyleHowtoformagoodprogrammingstyle1,sourceprogramdocumentation;2,datadescriptionmethod;3,statement4,inputandoutput.Note:prefacetheannotationandfunctionalannotation,sentencestructureclearfirst,efficiencysecond.2.2structuredprogramdesignFourprinciplesofstructuredprogrammingmethodis:1.top-down;2.stepbystep3.;modularization;4.Therestrictionoftheuseofthegotostatement.Thebasicstructureandcharacteristicsofstructuredprogramming:sequentialstructure:asimpleprogramdesign,thebasicstructure,themostcommonlyused;structure:alsocalledbranchstructure,includingsimpleselectionandmultibranchstructure,accordingtotheconditionsofJudge,shouldchooseabranchtoperformthecorrespondingsequenceofstatements;repeatstructure:alsoknownascyclicstructure,accordingtothegivenconditions,determinewhetheryouneedtorepeataThesameprocedure.3objectorientedprogrammingObjectorientedprogramming:attheendofthe60sNorwayUniversityofOsloandNorwaycomputercenterdevelopedSIMULAlanguageisthesymbolof.Theadvantagesofobject-orientedmethod:consistentwiththethinkinghabitsofhumanbeings;goodstability;goodreusability;tothedevelopmentoflarge-scalesoftwareproducts;(5)goodmaintainability.Theobjectisthemostbasicconceptofobjectorientedmethod,canbeusedtorepresentanyentityintheobjectiveworld,theLiketheabstractentity.Objectorientedprogrammingmethodintheobjectisusedtodescribearealsystemofobjectivethings,is.Asabasicunitofthesystem,asetofpropertiesthatrepresentitsstaticcharacteristicsanditcanexecuteasetofoperationgroupA.Theinformationcontainedintheobjectattribute,objectdescriptionofoperationexecutivefunctions,alsoknownasoperationmethodorserviceThebasiccharacteristicsoftheobject:identifyuniqueness;classification;polymorphism;package;(5)moduleindependently.Classisacollectionofobjectswithcommonpropertiesandcommonmethodsof.Itistheobjectoftheobjectisabstract.Aclassinstanceshouldbe.Themessageisthemessagebetweenaninstancewithanotherinstance.Themessageconsistsof(1)thenameoftheobjectthatreceivesthemessage;(2)themessageidentifier,ormessagename;(3)zeroormoreparameters.Inheritancereferstothedirectaccesstothenatureandcharacteristicsoftheexisting,withouthavingtorepeattheirdefinition.Theinheritanceofsingleinheritanceandmultipleinheritance.Singleinheritancereferstoaclassisallowedtohaveonlyoneparentclass,multipleinheritancereferstoaClassallowsmultipleparentclasses.Polymorphismreferstothesamemessagebydifferentobjectsacceptedcanleadtoatotallydifferentactionphenomenon.ThethirdchapterisbasedonSoftwareEngineering1basicconceptsofsoftwareengineeringComputersoftwareisasetofprocedures,includingdataandrelevantdocumentcomplete.Includingthecharacteristicsofthesoftware:softwareisalogicalentity;theproductionofsoftwareandhardwareisdifferent,ithasnoobviousproductionprocess;theuseofsoftwareintheoperation,doesnotexistduringthewearandagingproblem;thedevelopmentandoperationofsoftwareisdependentonthecomputersystem,computersystem,thisguideTheproblemofsoftwaretransplantation;thecomplexityofthesoftwareishigh,thecostofexpensive;thesoftwareinvolvesmanysocialfactors.Thesoftwareisdividedintoapplicationsoftwareandsystemsoftware,supportsoftware(orsoftware).Thesoftwarecrisisismainlymanifestedinthecost,quality,productivityandotherissues.Softwareengineeringistheapplicationofcomputersoftwareinthedefinition,developmentandmaintenanceofasetofmethods,toolsanddocumentation,Thestandardofpracticeandprocedure.Softwareengineeringincludes3elements:methods,toolsandprocesses.Thesoftwareengineeringprocessisputintothesoftwareoutputsasetofinterrelatedresourcesandactivities,including4basicActivity:P-softwarespecification;D--softwaredevelopment;C--software;A--softwareevolution.Software:softwareproductcyclefromputforward,implementationanduseofthemaintenancetostoptheuseofretirement.Thethreestagesofthesoftwarelifecycle:softwaredefinition,softwaredevelopment,operationandmaintenance,themainstageis:researchanddevelopmentprojectfeasibility;demandanalysis;softwaredesign;software;softwaretesting;operationandmaintenance.Thegoalofsoftwareengineeringandtheprincipleof:Objectives:atagivencostandschedule,developedwiththevalidity,reliability,understandabi1ity,canMaintainability,reusability,flexibility,portability,traceabilityandinteroperabilityandmeetuserneedsForproducts.Basicobjectives:topaylowerdevelopmentcosts;tomeettherequirementsofthesoftwarefunctionhasbetterperformanceofsoftware;Thedevelopmentofthesoftwareiseasytotransplant;needlowercost;tocompletethedevelopmentoftimelydeliveryontime.Abstract:thebasicprincipleofinformationhiding,modularity,localization,uncertainty,consistency,completenessandexperienceCertificateof.Studyonthetheoryandtechnologyofsoftwareengineering,themaincontentsinclude:softwaredevelopmenttechnologyandsoftwareengineeringmanagement.Includingsoftwaredevelopmenttechnology:softwaredevelopmentmethodology,developmentprocess,developmenttoolsandsoftwareengineeringenvironment.Includingsoftwareengineeringmanagement:softwaremanagement,softwareengineering,economics,psychologyandothercontentsoftware.Softwaremanagementincludingpersonnelorganization,schedule,qualityassurance,configurationmanagement,projectplanetc..Softwareengineeringprinciplesincludeabstraction,informationhiding,modularity,localization,uncertainty,consistency,completenessAndverification.3.2structuralanalysismethodThecoreandfoundationofthestructuredmethodisastructuredprogramdesigntheory.Demandanalysismethod(1)thestructuraldemandanalysismethod;(2)themethodofobjectorientedanalysis.Characteristicanalysismodelfromthedemandpoints:staticanalysisanddynamicanalysis.Theessenceofthemethodofstructuredanalysis:focusondataflow,top-down,layerdecomposition,processingsystemIntheprocess,thedataflowdiagramanddatadictionaryasthemaintool,thelogicmodelofthesystemisestablished.Thecommonlyusedtoolforstructuralanalysis(1)thedataflowchart;(2)thedatadictionary(3);decisiontree;decisiontable(4).Thedataflowdiagram:describesdataprocessingtools,saidlogicmodelneedstounderstandthegraphics,itstraightThefunctionofsystemmodeling.Datadictionary:onanorganizedlistofallsystemrelateddataelements,aswellasaccurateandstrictLatticedefinitionallowstheuserandsystemanalystforinputandoutput,storagecomponentandtheintermediateresultsareCommonunderstanding.Thedecisiontree:fromproblemdefinitiontextdescriptioncriteriatodistinguishwhatis,whatisthejudgmentconclusion,Accordingtothedescriptioninthematerialconditionstofindouttheconjunctionbetweenthesubordinaterelations,parallelrelationship,relationship,Accordingtotheirdecisiontreestructure.Decisiontable:similardecisiontree,whenthevalueofDFDdependsonmultiplelogicalconditions,i.e.Tocompleteasetofactionsoftheprocessiscausedbyacombinationofasetofconditionsofvalues,usingdecisiontabledescriptionSuitable.Thedatadictionaryisthecoreofstructuredanalysis.Thecharacteristicsofsoftwarerequirementspecification:correct;noambiguous;integrity;verification;consistency;comprehensible;traceability.3.3structuraldesignmethodThebasicgoalofsoftwaredesignistodeterminethetargetsystemtocompletethescheduledtaskswithmoreabstractwayAndthesoftwaredesignistodeterminethephysicalmodelofthesystem.Thesoftwaredesignisthemostimportantstepisthedevelopmentstage,willdemandaccuratelyintoacompletesoftwareproductorsystemTheonlyway.Fromatechnicalpointofview,thesoftwaredesignincludingsoftwaredesign,datastructuredesign,interfacedesign,processdesignStructuredesign:therelationshipbetweenthemainpartsofthedefinitionofsoftwaresystem.Design:dataanalysiswillbecreatedwhenthemodelistransformedintothedefinitionofthedatastructure.Interfacedesign:todescribehowthecommunicationbetweensoftwareandsoftware,internalcollaborationsystemandsoftwareandpeople.Thedesignprocess:thesystemstructurecomponentsintosoftwareprocessdescription.Fromtheprojectmanagementperspective:outlinedesignanddetaileddesign.Thegeneralprocessofsoftwaredesign,thesoftwaredesignisaniterativeprocess;advancedstructuraldesignforhighlevel;Afterthedesignprocessoflowlevel;withthedatadesignandinterfacedesign.Metricindependentuseofcouplingandcohesiontwoqualitativesoftwaremodule.Intheprogramstructuremorestrongcohesionofeachmodule,thenthecouplingisweak.GoodsoftwareshouldbeofhighcohesionandlowcouplingThebasictaskofdesignsoftwareis:(1)thedesignofsoftwaresystemstructure;(2)datastructureanddatabasedesign;(3)writtensummaryofthedesigndocuments;(4)summaryofthedesigndocumentsreview.Themoduleisrepresentedbyarectangle,thearrowindicatesthecallrelationbetweenmodules.Thestructurediagramcanalsouseannotatedarrowmodulecallsintheprocessofinformationtransferring.AlsoavailableWiththearrowroundsolidrepresentationoftransfercontrolinformation,thehollowcirculararrowisthedatatransferheartsaid.Thebasicformofstructure:basicform,orderform,repeatform,form.Therearefourtypesofmodulestructure:theafferentandefferentmodulemodule,conversionmoduleandcoordinationmodule.Typicaldatastream:therearetwotypesoftransformationtypeandtransactiontype.Transformtypesystemstructureiscomposedofinput,transformationandoutputcenterofthreeparts.Thecharacteristicsoftransactionaldataflowis:acceptatransaction,accordingtothecharacteristicsandthenatureofthetransaction,selecttheassignmentAnappropriateprocessingunit,thengivestheresult.Detaileddesign:determinetheimplementationalgorithmandlocaldatastructureforeachsoftwaremodulestructurediagram,withaAtooltoexpressalgorithmsanddatastructuresforthedetailsoftheselected.Processdesigntoolsarecommon:graphicaltools(flowchart)andforms(decisiontable),languageThetool(PDL).softwaretestingSoftwaretestdefinition:theuseofmanualorautomaticmeanstorunortestasystem,itspurposeistoCheckwhetheritmeetsthespecifiedrequirementsorbetweentheexpectedresultsandcleartheactualresultdifference.Thepurposeofsoftwaretesting:finderrorsandprocessexecution.Softwaretestingmethods:statictestinganddynamictesting.Thestatictestincludescodetest,staticstructureanalysis,codequalitymetrics.Nottheactualoperationofthemainsoftware.Throughthemanual.Thedynamictestis:basiccomputertest,includingwhiteboxtestingandblackboxtestingmethod.Whiteboxtesting:insidetheprogramismainlyusedtoverifythecompletionofsoftwareinternaloperations.Themainmethod.Seriescoverage,basicpathtest.Blackboxtesting:themaindiagnosticfunction,interfaceerror,wrongormissingdatastructureorexternaldatabaseaccessErrorperformance,error,initializationandterminationconditionsforfault,softwarevalidation.ThereisthemainmethodofequivalenceclasspartitionMethod,boundaryvalueanalysis,errorguessingmethod,causalitydiagrametc..Thesoftwaretestingprocessaccordingto4steps:unittesting,integrationtesting,acceptancetesting(validationtest)andsystemtesting.debuggingprogramProgramdebuggingtaskistodiagnoseandcorrecttheerrorsintheprogram,mainlyinthedevelopmentstage.Thebasicstepsofprogramdebugging:positioningerror;designandmodifycode,toeliminatetheerror;regressiontesting,topreventtheintroductionofnewerror.Softwaredebuggingcanbedividedintostaticanddynamicdebuggingdebuggingtable.Staticdebuggingmainlyreferstothroughthepeople,sthinkingtoanalyzethesourceProgramcodeanddebugisthemaindesignmethod,dynamicandstaticdebuggingdebuggingassistant.Themaintestmethod.Method:forceddebuggingmethod;backtracking;causeelimination.Thefourthchapterbaseddatabasedesign1basicconceptsofdatabasesystemThedataisactuallydescribed:symbolofthings.Thecharacteristicsofthedata:thereisacertainstructure,typeandvalueofthepoints,suchasinteger,real,characteretc..ButthedataThevaluegiveninaccordancewiththesettingvalue,suchastheintegervalue15.Thedatabaseisacollectionofdatastructureswithuniformandstoredinthestoragemediumismoreuniform,Theintegratedapplicationofthedata,andcanbeofvariousapplicationsharing.Thedatabasestoringthedataisstoredaccordingtothedataprovidedbythedatamodel,withthecharacteristicsofintegrationandsharing.Databasemanagementsystem:asystemfordataorganization,datamanipulation,datadimensionSupport,controlandprotectionanddataservices,isthecoreofdatabase.Databasemanagementsystem:thedatamodeldefinition:thatis,fortheconstructionofthedataframedatabase;physicaldataaccessconstruction:providesaccesstoeffectivemethodforconstructingthephysicalmodelanddataaccessAndmeans;datamanipulation:toprovideconveniencefortheusersofthedatabasedata,suchasquery,insert,modify,deleteInaddition,simplearithmeticandstatistics;dataintegrity,safetyinspectionanddefinition;concurrencycontrolandfaultrecoverydatabase;dataservicessuchascopy,conversion,reorganization,performancemonitoringandanalysis.Inordertofulfilltheabovesixfunctions,thedatabasemanagementsystemprovidesthefollowingdatalanguage:datadefinitionlanguage:physicalaccessdatadefinitionanddatamodelforconstruction;:datamanipulationlanguagefordatamanipulation,suchasadd,delete,queryandetc.;datacontrollanguage:responsiblefordataintegrity,securityandconcurrencycontrol,definitionandcheckitFaultrecovery.Accordingtothedatalanguageusehastwostructuralforms:interactivecommand(alsoknownasselfcontainedorindependent.Thehostlanguage(words)canbeembeddedinsomehostlanguage).Thedatabaseadministrator:professionalmanagementpersonnelplanning,design,maintenanceandmonitoringofthedatabase.Databasesystem:thedatabase(data),databasemanagementsystem(software),thedatabaseadministrator(peopleMember),hardwareplatform(hardware)andsoftwareplatform(software)fivepartsconstitutetheoperatingentity.Thedatabaseapplicationsystemiscomposedofdatabasesystem,applicationsoftwareandapplicationinterfacethree.Filesystem:providesasimpledatasharinganddatamanagementcapabilities,butitcannotprovideacompleteTheabilityofmanagement,datasharingandunified.Hierarchicaldatabaseandnetworkdatabasesystem:toprovideastrongsupportfortheunityandsharingofdata.TherelationaldatabasesystemThebasiccharacteristicsofthedatabasesystem:integration,datasharingofhighandlowredundancy,dataindependence(ofphysicalindependenceandlogicalindependence),unifieddatamanagementandcontrol.Threelevelmodelofdatabasesystem:conceptualmodel:globaldatalogicalstructureofthedatabasesystemisdescribed,thepublicdatatoallusersasFigure;externalmode:submodeandusermode.Istheuser'sviewofdata,whichistheuserseeThedatamodel;inthemodel:alsoknownasthephysicalmodel,itgivesthedatabasephysicalstoragestructureandphysicalaccessmethod.Thetwolevelmappingdatabasesystem:theconceptofmappingmodetothemodeof;mappingmodetotheconceptualmodel.2datamodelTheconceptofdatamodel:datafeatureabstract,fromtheabstractleveltodescribethestaticcharacteristics,dynamicsystemBehaviorandconstraintsfordatabasesystemsandinformationtableoperationprovidesanabstractframework.DescriptionDatastructure,datamanipulationanddataconstraints.ThebasicconceptofE-Rmodelentity:thethingsintheworld;attributes:thecharacteristicsofthings;(3):therelationshipbetweenthingsintherealworld.Therelationshipbetweenentitysethasonetoone,onetomanyandmanytoMultilink.CouplingrelationshipbetweenthethreebasicconceptsofE-Rmodel:theentityisthebasicunitintheconceptualworld,attributeAttributedomain,eachentityattributevaluewithindesirabledomain.Alloftheattributesofanentitycalledtuplevalues.ThemethodofE-Rmodel:(1)theentitysetrepresentation;(2)attributetablemethod;(3)contactmethod.Thebasicstructureofthehierarchicalmodelisatreestructure,hasthefollowingcharacteristics:eachtreehasonlyonerootnodecalledorphan;inthetreeexceptallthenodeshaveoneandonlyoneparent.Fromthegraphtheory,thenetworkmodelisonewithoutanylimitationoftheundirectedgraph.Therelationshipmodelusingtwo-dimensionaltablesaid,referredtoasthetable,tableandtableframe