HBSTR-treeleafnodes
ThehybridindexmethodHBSTR-treethatintegratesR-tree,hashtableandB*treeisadopted,asshowninFigure1TheprincipleandframediagramofHBSTR-tree.3Thefunctionsoftheseedindexstructureareasfollows:(1)R-treeisthemainindexstructure,whichisusedtorealizethespace-timerangequery;(2)Hashtableistheauxiliarystructure,whichmaintainsthelatesttrajectorynodeofthemovingobject,andisusedforgroupinsertionsamplingPoint;(3)B*treeisasecondaryindexstructure,aone-dimensionalindexoftrajectorynodes,whichisusedtorealizethetrajectoryqueryofthetargetobject.
Samplingpointscontaindataitemssuchasobjectidentifiers,timestamps,andspatiallocations.Duetofactorssuchassensorocclusionorinstability,thespatiallocationdataofsamplingpointsmaybegrosslyinaccurate.Generally,certaindatacleaningmethodsareusedtofilterGrosserrordata.Thenumberofsamplingpointsforasinglemovingobjectistensofthousands.Distributedmanagementofsamplingpointsisnotconducivetofindingtrajectories,andwillhaveanegativeimpactonstorageutilizationandcreationefficiency.
Hashtableisusedtomanagethelatesttrajectorynodeofallobjects,whichisconvenientforfindingthelatesttrajectorynodeofanobjectthroughtheobjectidentifier.Whenatrajectorynodeisfull,inserttheRtreeandcreateanewtrajectorynodetoreceiveanewtrajectorynode.Samplingpoint.Inthisway,thewayofinsertingthespatio-temporalR-treeingroupsintheformofnodescangreatlyimprovetheefficiencyofindexcreation.
IntheHBSTR-tree,theRtreeisaspatiotemporalRtreewithN+1dimensions(Nisthespatialdimension,and1referstothetimedimension),andtheminimumboundingboxMBRoftheR-treenodeisthespatiotemporalcoordinatesofitschildsetTheminimumrangeoftheaxis,thetimereferenceusestheabsolutenumberofsecondssince1970asthebenchmark.TheabovetrajectorynodeisusedastheleafnodeoftheRtree.Anewnodeinsertionalgorithmisusedtoinsertitsindexentryintotheupperlayeroftheleafnodelayer,andthespatio-temporalR-treestructureisoptimizedbyusingnodeselectionandnodesplittingsub-algorithms.Spatio-temporalR-treesupportsmultiplequerytypes,suchassearchingforobjectcollectionsandobjecttrajectorieswithinacertaintimeandspace,orobjectcollectionsandobjectpositionswithinacertainspaceatacertaintime,orthenearestneighborsofacertainspatialpointatacertaintime.Thespatio-temporalR-treeisnotefficientinsearchingthetrajectoryofthetargetobjectinacertainperiodoftime.Tosolvethisproblem,theone-dimensionalkeycode(OID+tTimeStart)composedoftheobjectidentifierOIDofthetrajectorynodeandthestarttimetTimeStartisusedtoconstructtheB*treeindexofthetrajectorynode.Theobject'strajectorynodeatacertainmoment,usingthebidirectionalpointerbetweentheB*treebrothernodestotracethetrajectory.Thetrajectorynodeusuallycontainsnearlyahundredconsecutivesamplingpoints.Comparedwiththeone-dimensionalindexstructureofdirectsamplingpoints,thismethodsavesmorethan90%ofstoragespace.
Indexleafnode
TakethecreationofaB-treeindexonthednamecolumnofthedepttableasanexample.Becausethedepttablehasonly4rowsofrecords,theindexonthednamecolumnonlyneedsoneleafnode,Thatis,onedatablockcanstoreallindexdata.Thecontentofthisleafnodedatablockisthesorteddnamecolumnvalueandtherowidoftherecordwherethecorrespondingcolumnvalueislocated.Therowidhereonlyincludesthefilenumber,thedatablocknumber,andthedatarecordedinthedataTheaddressintheblockdoesnotincludetheobject_idpartinthepseudocolumnrowidofthedepttable.
Thestorageformatoftheindexintheleafnodedatablockissimilartotherowdatastoragemethodofthetable.Eachcombinationofindexcolumnvalueandrow-idcanberegardedasarowofrecords.TheserowsarefromthedatablockStartfillingattheendofeachrow,andtheaddressrecordedinthedatablockforeachrowisstoredintheslotattheheadoftheblock.Ifanindexiscreatedonthednamecolumnofthedepttable,itconsistsofonlyoneleafnode.Figure2showsthestructureoftheleafnodeoftheB-treeindex.AscanbeseenfromFigure2,therowidpartoftheB-treeindexleafnodeiscomposedof48bits,thefirst10bitsrepresentthefilenumber,themiddle22bitsrepresenttheblocknumber,andthelast16bitsrepresenttherownumberintheblock.Thatistheslotnumber.
ATMleafnode
Introduction
Itisrelativelysimpletocreatealeafnodeinamulticastgroup.InanATMnetwork,asa"leafnode",youmustListenforinvitationsfroma"rootnode"tojoinagroupbyyourselfanytime,anywhere.Itisworthnotingthatatanygivenmoment,Windows98andWindows2000canonlysupportoneATMleafnode.Inotherwords,foranyATM"point-to-multipoint"session,withinthescopeoftheentiresystem,onlyoneprocesscanbecomeitsleafmember.
Creationsteps
IntheATMnetwork,thestepstocreatealeafnodeare:
(1)UsetheWSASocketfunctiontocreateasetofaddressfamilyAF_ATMConnection,setthetwoflagsWSA_FLAG_MULTIPOINT_C_LEAFandWSA_FLAG_MULTIPOINT_D_LEAFatthesametime.
(2)UsethebindfunctiontobindthesockettothelocalATMaddressandport.
(3)Callthelistencommand.
(4)UseacceptorWSAAccepttowaitfortheinvitation.Asforwhichcommandisused,itdependsonwhichI/O(input/output)modelisused.Aftertheconnectionisestablished,theleafnodecanstarttoreceivedatafromtheroot.ForATMmulticast,thedataflowmustbeone-way,fromtherootnodetotheleafnode,irreversible.
IPleafnode
Introduction
TheprocessofjoininganIPmulticastgroupforaleafnodeisrelativelysimple,becauseeachnodeisa"leafnode",soThestepstakenwhenjoiningagrouparethesame.SinceIPmulticastcanbeimplementedinbothWinsock1andWinsock2,thesamethingcanbedonethroughtwoAPIcallmethods.Itisworthnotingthatifanapplicationonlyintendstosenddata,itdoesnothavetojoinanIPmulticastgroup.Whensendingdatatoamulticastgroup,thedatapacketstransmittedinthenetworkareroughlythesameasordinaryUDPpackets,exceptthatthedestinationaddressisreplacedwithaspecialmulticastaddress.Butifyouwanttoreceivemulticastdata,youmustjoinagroup.Butinanycase,exceptfortherequirementsforgroupmembership,IPmulticastcommunicationisnodifferentfromordinaryUDPprotocolcommunication,becausebothare"connectionless"and"unreliable".
Creationsteps
InWinsock1,thebasicstepstocreateleafnodesrequiredforIPmulticastcommunicationare:
(1)CreateusingsocketfunctionAsocket,payattentiontotheAF_INETaddressfamilyandSOCK_DGRAMsockettype.Toinitializeamulticastsocket,youdon'tneedtosetanyspecialflags,becausethesocketfunctionitselfdoesnotprovideflagparameters.
(2)Ifyouwanttoreceivedatafromthegroup,youneedtobindthesockettothesamelocalport.
(3)CallthesetsockoptfunctionandsettheIPADDMEMBERSHIPoptionatthesametimetospecifytheaddressstructureofthegroupyouwanttojoin.
IfyouareusingWinsock2,thensteps(1)and(2)arethesame,andstep(3)shouldbereplacedbycallingtheWSAJoinLeaffunctiontoaddtheleafnodetothatgroup.
OSGleafnode(Geode)
TheGeodeclass(GeometryNode)isequivalenttotheleafnodeinOSG.Ithasnochildnodes,butcontainstheosg::Drawableobject,andtheosg::Drawableobjectstoresthegeometrytoberendered.Generally,thedrawablegeometryispassedtotherootnodeforrenderingthroughtheGeodenode.TheGeodenodeisthehighestmanagementnodeforOSGgeometricdrawing.