toprovideacompletesetofoperationalcapabilitieswithrequiredefficiencyonalargescaleitappearstodaythattechnologicalimprovementsinprovidingfasterandmorereliablehardwaremayanswerthequestionpositively.
Thehierarchicaldatamodelisbasednoatree-likestructuremadeupofnodesandbranchesanodeisacollectionofdataattributesdescribingtheentityatthatopinethehighestnodeofthehierarchicaltreestructureiscalledarootthenodesatsucceedinglowerlevelsarecalledchildren.
Ahierarchicaldatamodelalwaysstartswitharootnodeeverynodeconsistsofoneormoreattributesdescribingtheentityatthatnodedependentnodescanfollowthesucceedinglevelsthemodeintherecedinglevelbecomestheparentnodeofthenewdependentnodesaparentnodecanhaveonechildnodeasadependentormanychildrennodesthemajoradvantageofthehierarchicaldatamodelistheexistenceofprovendatabasemanagementsystemsthatusethehierarchicaldatamodelasthebasicstructurethereisareductionofdatadependencybutanychildmodeisaccessibleonlyinaclumsywaythisoftenresultsinaredundancyinstoreddata.
Thenetworkdatamodelinterconnectstheentitiesofanenterpriseintoanetworkinthenetworkdatamodeladatabase.
Consistsofanumberofareasanareacontainsrecordsinturnarecodemayconsistoffieldsasetwhichisagroupingofrecordsmayresideinanareaorspananumberofareasasettypeisbasedontheownerrecordtypeandthememberrecordtypethemany-to-manyrelation-shipwhichoccursquitefrequentlyinrapfifecanbeimplementedeasilythenetworkdatamodelisverycompeltheapplicationprogrammermustbefamiliarwiththelogicalstructureofthedatabase.
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哈尔滨工业大学成人高等教育毕业设计(论文)
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