eXtendablexyq.163.cbg.com

RESEARCHONADISTRIBUTEDARCHITECTUREOFMOBILEGISBASEDONWAPWangFangxionga,JiangZhiyongbaResearchCentreofSpatialInformationandDigitalEngineering,WuhanUniversity,129LuoyuRoad,Wuhan430079,China.
wfxwhu@163.
combStateKeyLaboratoryofInformationEngineeringinSurveying,MappingandRemoteSensing,WuhanUniversity,129LuoyuRoad,Wuhan430079,China.
houyingzi@sohu.
comCommissionVI,WGVI/4KEYWORDS:MobileGIS,Architecture,J2EE,WAP,MobileInternetABSTRACT:MobileGeographicalInformationSystem(MobileGIS)isaGeographicalInformationSystembasedonmobilecomputingandmobileInternet.
ItisnotaconventionalGISmodifiedtooperateonasmallercomputer,butanextensionofWebGIStomobileInternetincludingwirelessInternet/Intranetandmobilecommunicationnetwork.
ButarchitecturesofWebGISareunsuitableforMobileGIS,becauseofseveralbottleneckssuchasthelow-bandwidthofwirelessnetwork,thediversityofmobiledevices,limitedprocessingpowerandscreendisplaylimitationofmobiledevicesandthediversityofmobilesystemplatform.
SotheresearchonthearchitectureofMobileGISishotintheGISfield.
WAP-basedMobileGIScanbedescribedasmobileuserscanperformthealmostsamefunctionalityasofWebGISbutinamobileenvironmentatanytime,anyplaceandwithoutthelimitationofoperatingsystemandwiredlink.
Inthispaper,adistributedarchitectureforWAP-basedMobileGISisproposed.
UsingJavaServletEnginetechnologyandspatialinformationWebcachingmechanismatthefatserverside,thearchitecturebasedonJ2EEiscomposedoffourlogictiers:presentationtier,WAPservicetier,applicationtieranddataservicetier.
Aprototypesystembasedonthearchitecturehasbeendeveloped.
ItcansuccessfullyworkonWAPphones,whichprovesthatthearchitectureisfeasible.
1.
INTRODUCTIONSince1990,geospatialinformationtechnologiesandmobilewirelessInternethavebeenrapidlydeveloped.
ItiseasytoseethattheintegrationofgeospatialinformationandmobileInternetisinevitable,whichissimultaneitydrivenbymarketdemandsandtechnologies(LiDeren,etal,2002).
Theintegratedsystemisdesignedtoworkonmobileintelligentterminals,andbringsnewdimension-atanytime,anyplace-toaccessgeospatialandattributeinformationinGIS.
ItiscalledMobileGeographicInformationSystem(MobileGIS).
MobileGISoffersanothernewperspectivefortheuseofGISandfurtherextendsthe"office"GISworksinmobileenvironment(ShiWenzhongandKwanKawai,2002).
MobileGISwasearlyappliedtoassistofficeandcollectdatainthefield(NessS.
T.
Lee,1993;K.
North,1997).
ItisnotaconventionalGISmodifiedtooperateonasmallercomputer,butasystembuildusingafundamentallynewparadigm(DavidMaguire,2001).
ItextendsunlimitedinformationontheInternetandpowerfulservicefunctionsofGIStomobiledevices,andcanprovidemobileuserswithgeospatialinformationservices.
MobileGIScreatesanewchannelofbusinesspractice,andthousandsofpotentialapplicationsandservicescanalsobedeveloped.
Hence,itisexploringaneweraofmobilegeographicinformationservices.
Therestthispaperisarrangedasfollow:WAP-basedMobileGISanditssuperioritytoSMS/MMS-basedMobileGISarebrieflyintroducedinSection2.
ThreemainstreamarchitecturesolutionsfordistributedsystemsarepresentedinSection3.
AdistributedarchitectureforWAP-basedMobileGISbasedonJ2EEisproposedinSection4.
AndaprototypesystemimplementedbasedonJ2EEispresentedinSection5.
Finally,theconclusionisdrawnandoutlookofWAP-basedMobileGISarediscussed.
2.
MOBILEGISBASEDONWAPMobileGIScanbesimplydividedintotwocategories,accordingtocurrentlypopularsolutionsaccessingtotheMobileInternet.
TheoneisbasedonShortMessageService(SMS)/MultimediaMessageService(MMS),theotherisbasedonWirelessApplicationProtocol(WAP).
SMS/MMS-basedMobileGIS(MaLingbin,etal,2002;WeiZhongya,etal,2002;ZhangJianqunandLiangJuanzhu,2003)canonlybesuitableformobilephoneswithsamplesystemfunctions,unfriendlygraphicaluserinterface(GUI),poorinformationpresentationandtherestrictedapplicationfields,becauseofthelimitationsofSMS/MMSsuchasrestrictedcarryinginformation,timelag,unfriendlyinteractivemode,andsoon.
Onthecontrary,WAPisabear-independentinternationalstandardprotocolthathasoptimizedformobiledeviceswithlimiteddisplayandsmallkeyboardsofmobilehandsetsandlowbandwidthsofwirelessnetworks,andpermitsapplicationsandservicestooperateoverallexistingandforeseeablewirelessnetworkssuchasGSM,CDMA,PHS,TDMAandWCDMA(WAPForum,2002).
TheWAPspecificationencompassesarelativelysimpleandcompactversionofXML(eXtendableMarkupLanguage)calledWML(WirelessMarkupLanguage),whichmakesitpossibletomakerequeststoamobileservicefromamobileterminalandreturnamapintheformofanembeddedbitmap(e.
g.
WBMP).
SoWAP-basedMobileGIShasricherinformationpresentation,friendlierGUI,moresystemfunctionsandmoreapplicationfieldsthantheformer.
Moreover,itcanworkonawiderangeofmobiledeviceswithaWAPmicrobrowseronly,fromPersonalDigitalAssistants(PDAs),mobilephones,andin-carcomputerstoothersmallmobiledevices,andkeepsthestandardbrowsingstyle.
WAP-basedMobileGIScanbedescribedasmobileusers(withaWAPmobileterminalonly)canperformthealmostsamefunctionalityasofInternetGISbutinamobileenvironmentatanytime,anyplaceandwithoutthelimitationofoperatingsystemandwiredlink.
Altogether,itisbecauseoftheadvantagesofWAPthatwebelieveWAP-basedMobileGISwillplayaleadingroleinourmobileinformationservicesmarkets.
Theframeworkandsoulofadistributedsystemisthesystemarchitecturedecidingthedistributionofsystemfunctionsanddata.
WAP-basedMobileGIS,asanewdevelopmenttoInternetGIS,isstillinapreliminarystage,whoseresearchissuesneedbedealwith.
However,thearchitecturesolutiontoWAP-basedMobileGISisthekeyandcoreofitswholeresearches.
AlthoughLiDeren,etal(2002)andLiLuqun,etal(2002)usedtopresentanarchitectureforMobileGISrespectively,thearchitectureswereconceptualonesandhaddifficultyplayingasubstantiallydirectiveroletobuildingaMobileGISsystem,letaloneWAP-basedMobileGIS.
3.
ARCHITECTURESOLUTIONSWAP-basedMobileGISisa"thinclient"distributedsystemviamobileInternet.
Itmustbeanopen,extendable,stableandcross-platformdistributedsystem,becauseoftheincreasingapplicationdemandsandthediversityofmobileterminals.
Currently,popularsystemarchitecturesolutionsfordistributedsystemsareallbasedondistributedobjecttechnologies.
Therearethreemainstreamindustrystandards:Microsoft'sWindowsDistributedNetworkArchitecture(WindowsDNA)/.
NETArchitecture,ObjectManagementGroup'sCommonObjectRequestBrokerArchitecture(CORBA),Sun'sJava2EnterpriseEdition(J2EE)Architecture.
AsystembasedonWindowsDNA/.
NETArchitecturesolutioncanonlyuseMicrosoft'splatformsfromdevelopment,deploymenttorunning,includingdevelopingplatformsandoperatingsystem.
Itcannotcrossoperatingsystemplatformespecially,whichisthefatalweaknessofWindowsDNA/.
NETArchitecture.
CORBAistoohugeandcomplicated.
Anditstechnologiesandstandardsareupdatedrelativelyslowly.
J2EEisaspecificationandstandardcreatedbySunandherindustrypartners,anditevolvesquickly.
J2EEprovidessupportforthetechnologiessuchasEnterpriseJavaBeans(EJB),JavaServletsAPIandJavaServerPagers(JSP),andsoon.
J2EEsolutionreducesthecostandcomplexityofdevelopingamulti-tierdistributedsystemwhichcanberapidlydevelopedanddeployed,andcanenhancetheportability,security,loadbalancingandextensibilityofadistributedsystem.
TherearethefollowingadvantagestobuilddistributedGISbasedonJ2EE(MaoHaifeng,2004):(1)cross-platform;(2)multi-tierseparatingtocomplicatedtasks;(3)componentreusingand(4)moduledeveloping.
Thus,J2EEsolutioncansatisfythesystemrequirementsofWAP-basedMobileGIS.
BasedonJ2EE,thispaperproposesadistributedarchitectureforWAP-basedMobileGIS.
4.
ADISTRIBUTEDARCHITECTUREAsshowedonFigure1,theJ2EE-baseddistributedarchitectureiscomposedoffourlogictiersfromtheclientsidetotheserverside:presentationtier,WAPservicetier,applicationtieranddataservicetier.
Atthefatserverside,GeospatialinformationWebcachingmechanismisusedtooptimizetheperformancecapabilityandreducingtheaccessdelayoftheclient.
Functionsandcomponentsofeachlogictierandthestatementaboutthedistributionofpresentationlogic,businesslogicandgeospatialdatainthearchitecturearedetailedlystatedasfollow.
MobileClientWAPMicroBrowserJ2MEApplicationPDA/phone/in-carPCWAPGatewayWMLEncoderWMLScriptDecoderWebServerJSPPresentingServletIdentifyingServletServletEngineWebContainerApplicationServerGISSessionBeansGISEntityBeansEJBContainerSDE+RDBMSDatabaseServerLegacysystemWAPHTTPRMIJDBCJMSMobilePositionCentreMLPWirelessnetworkInternetIntranetFigure1:AdistributedarchitectureofWAP-basedMobileGIS4.
1PresentationTierPresentationtierisacarrieroftheclientofWAP-basedMobileGIS,andismainlyresponsibleforimplementingthepresentationlogicofGISdata.
Generally,theclientwithoutlocal-storagedataisaWAPmicrobrowserthatcontrolstheGUIandisanalogoustoastandardWebbrowser.
TheWAPmicrobrowserneedn'tperformanyGISbusinesslogic,don'tdirectlyconnecttoaback-enddatabaseserver,anddon'tstoreitselfstateinformation,soitisareally"ThinClient".
TheclientalsomaybeaJ2ME(Java2MicroEdition)application.
4.
2WAPServiceTierWAPservicetierincludesaWAPProxy(oftenreferredtoasaWAPGateway)andaWebServer.
TheWAPGatewaywasrequiredtohandletheprotocolinterworkingbetweentheclientandtheWebServer.
AsdepictedinFigure1,theWAPGatewayconsistsofWMLencodersandWMLScriptdecoders.
TheWAPGatewaycanoptimizethecommunicationprocessandmayoffermobileserviceenhancements,suchaslocation,privacy,andpresencebasedservices.
TheWAPGatewaycommunicateswiththeclient(WAPmicrobrowser)usingtheWAPprotocols,anditcommunicateswiththeWebServerusingthestandardInternetprotocolssuchasHTTP/HTTPS.
OncetheWAPGatewayreceivesWAPrequestsfromtheclient,ittranslatestherequeststoHTTPrequests,andthensendsthemtotheWebServer.
OncetheWAPGatewayreceivesHTTPresponses(webcontents)fromtheWebServer,ittranslatesthewebcontentstocompactencodedbinaryformatsforreducingthesizeandnumberofpacketstravelingoverthewirelessnetworktotheclientfordisplayingand/orprocessing.
TheWebServerincludesaWebContainerandWebprotocolssupport,securitysupport,andsoon.
WebcachingmechanismforGeospatialInformationTheWebContainerisresponsibleformanagingaJavaServletEngineandJavaServerPagers(JSP).
AnInternetGISsystembasedonJavaoftenusesJavaAppletsand/orServletstoextendthedynamicallydisplayingfunctionalityfortheWebbrowser.
ThispaperusesaServletEngineinsteadofrunningAppletsand/orServletsinsidetheWebServer,whichhasseveraladvantagesasfollow:1TheServletEnginerunsitselfinsidetheWebServer.
ButappletsinsidetheWebServermustbedynamicallydownloadedtotheclientforprocessing,whichwouldincreasetheloadofwirelessandmobiledevices(Especially,aWAPphonehasnotthecapabilityofrunningapplets.
).
2TheServletEnginecanhostServletsandprovidethemwithstandardJavaServletAPIs.
3TheServletEnginedecouplesServletsprocessingfromspecificimplementationdetailsoftheWebServer.
Thisincreasestheflexibilityofthesystemarchitecture,asitallowstheWebServertochangewithoutimpactingontheoverallsystem.
TheServletEnginecanalsoprovidevariousmanagementfeaturesthathelptoshifttheloadofServletsprocessingawayfromtheWebServer.
TheclientdevicesofWAP-basedMobileGIShaveseveraltypes(e.
g.
PDAandWAPphone)whosedisplayingandpresentingcapabilitiesaredifferent.
Sotheremusthasamechanismattheserverside,thatis,theWebServermaydeterminethetypeoftheclientdeviceandgeneratecorrespondingpresentationlogicfortheclient.
Fortunately,theServletEnginecansolvetheproblemeffectively.
TheServletEnginemayprovidetwokindsofServlets:theoneispresentingServletwhichisresponsibleforgeneratingcorrespondingpresentationlogicaccordingtothetypeoftheclientdevicefortheclient;theortherisidentifyingServletwhichisresponsiblefordeterminingthetypeoftheclientdevice(throughtheonlyIDoftheclientdeviceaccessingmobilenetworks)andthennotifypresentingServlet.
TheServletEngineisresponsibleformanageServletsandprovidesupportforJSP.
SinceServletsruninsidetheWebServer,everyonedoesnotneedaGUI.
Servletsinthesameservletenginecanshareresourcesandchaintogether.
SotheWebServercangeneratedynamicalWebcontentsbyrunningServlets(i.
e.
presentingServlets)toresponseforclientrequestslikeCGI.
AndServletsaremoreefficientthantheCGIapproachandtheFast-CGIapproach.
ThroughServletsand/orJSP,theclientsidemayindirectlyperformEJBcomponentsinsidetheApplicationServertoimplementGISbusinesslogic,suchasspatialanalysis,spatialandattributequerying,routeplanning,geocodingandgazetteer,andsoon.
4.
3ApplicationTierApplicationtieristhecoreofthearchitecture.
ItcorrespondsGISApplicationServersthatcommunicatewiththeWebServerinWAPservicetierthroughRemoteMethodInvocation(RMI).
AnEJBcontaineratanApplicationServeristheruntimeenvironmentofEJBcomponentsincludingGISSessionBeansandGISEntityBeans,andcontrolsthesecomponentstobeperformedandtransferred.
Atthesametime,thecontaineralsoprovidesthesecomponentswithallrequiredservicesfordistributedcomputingenvironments.
Thus,theseEJBcomponentscouldmoreefficientlyexecuteintheApplicationServer.
TheEJBcomponentscanuseJDBC(JavaDatabaseConnection)technologytoaccesstodatabaseservers,anduseJMS(JavaMessageService)technologytoconnecttoback-endlegacysystems.
TheApplicationServerhasaspecialLocatingEntityBeantocommunicatetheMobilePositionCentre(MPC),aServerprovidinggeographiclocationinformation,withMobileLocationProtocol(MLP)(LocationInteroperabilityForum,2002).
Themobilepositiontechnologiesforreal-timecapturingthelocationinformationofmobileusersgenerallyareGPS,CellOfOrigin(COO),TimeOfArrival(TOA),AngleOfArrival(AOA),EnhancedObservedTimeDifference(E-OTD)andsoon.
4.
4DataServiceTierDataservicetiercorrespondsDatabaseServersthatareusedtomanageandstoregeospatialandattributedataofthewholesystem.
Objectorienteddatabasemanagementsystem(OODBMS)isthemostdesireddatabaseserverforaGISsystem,butOODBMSisimmatureandverycostlycurrently,soitisnotpopularandtobeusedcommonly(GongJianya,2001).
Atpresent,themainstreamsolutionisthatlargeobject-relationdatabasesystemssuchasDB2,Oracle,Sybase,SQLServer,andsoonareusedtomanageandstoreGISdata,atthesametime,spatialdataengine(SDE)alsocanbedevelopedtobuildthecommunicationbetweendataservicetierandapplicationtier.
SDEisanopenstandards-basedmiddlewaresuchasArcSDE,SpatialWareandOracleSpatial.
5.
J2EE-BASEDPROTOTYPESYSTEMUsingthe100%PureJavaJ2EEsolution,theabovearchitectureisopenandcross-platform,andhasthecharacteristicssuchasextensibility,stabilityandreliability,whichcouldsatisfysystemrequirementsofWAP-basedMobileGIS.
Basedonthearchitecture,aprototypesystemofWAP-basedMobileGIShasbeendeveloped.
Intheprototypesystem,theserversideusesApacheTomcat5asthewebserver,BEAWebLogic8.
1astheapplicationserver,Oracle8iandESRIArcSDEasthedatabaseserver,anditprovidesarangeofbasicGISfunctions(e.
g.
spatialandattributequerying,routeplanning,geocoding,mapping,etc.
)toaMobileGISuserusingtheServletEngineandEJBcomponentstogainandprocessspatialgeometryobjectinback-endspatialdatabases.
TheclientsideusesWAPphonewithaWAPmicrobrowserandmayobtainmapsinWBMPformatfromtheserverside,andithasthebasicmapbrowsingfunctionssuchaszoomingout,zoomingin,moving(up,down,leftandright).
TherunningresultsareshowedinFigure2.
Figure2:AprototypesystemofWAP-basedMobileGIS6.
CONCLUSIONANDPROSPECTWAP-basedMobileGISisaverynewstudyfieldofGeoinformatics.
Aboveall,thearchitectureissolved,becauseitisthekeyandcoreofthedistributedsystem.
Inthispaper,basedonJ2EE,anopendistributedarchitectureisproposedforWAP-basedMobileGIS.
Andaprototypesystemisdesignedanddevelopedbasedonthearchitecturewhichiscomposedoffourlogictiers.
TheprototypesystemcansuccessfullyworkonWAPphones,whichprovesthatthearchitectureisfeasible.
Atpresent,lowbandwidthsarestillthemainbottleneckofallmobileapplications(WeiZhongya,XuSunxinandWuLun,2003).
Soresearchesontheorganizationofgeospatialdataatthefatserversideandonthepresentationofgeospatialinformationatthethinclientsideshouldbedonefarther.
Fortunately,themobilenetworkistowardsthedevelopmentof3G.
In3Gage,whenthemobileterminalmovesatthesamespeedasvehicle,thetransmissionspeedis144kbps,whenthemobileterminalmovesatthewalkingspeedorun-movesinoutdoor,thetransmissionspeedis384kbps,whenthemobileterminalisintheroom,thetransmissionspeedisupto2Mbps.
The3Gbandwidthswillsatisfywiththerequirementsofgeospatialinformationwirelesstransmission.
Therefore,itisnothardtounderstandthatWAP-basedMobileGISwillhavebetterdevelopmentandapplicationperspectivesandconsiderablebusinessvalue.
REFERENCESLiDeren,LiQingquan,XieZhiying,ZhuXinyan,2002.
TheTechniqueIntegrationoftheSpatialInformationandMobileCommunication.
GeomaticsandInformationScienceofWuhanUniversity,27(1):1-6.
ShiWenzhong,Ka-waiKwan,2002.
:AReviewandAnalysisofMobileGISDevelopment.
TheInternationalWorkshoponMobileandInternetGIS.
Wuhan,2002.
NessS.
T.
Lee,1993.
SingleLineStreetNetwork:TheFoundationofMobileGIS.
IEEE-IEEVehicleNavigationandInformationSystemsConference.
Ottawa-VNIS'93,34-37.
K.
North,1997.
FieldInformationSystemsforManagingYourAssets.
EngineeringtheBenefitsofGeographicalInformationSystems.
IEEEColloquium,1997,6/1-6/7.
DavidMaguire,2001.
MobileGeographicServicesComeofAge.
Geoinformatics,March,6-9.
MaLinbing,GongJianya,ZhangChunSen,2002.
ResearchonApplicationSolutionandKeyTechnologyofMobileGIS.
ISPRS,VolumeXXXIV,Part2,CommissionII:323-326.
WeiZhongya,XuSuning,WuLun,2002.
AModelofMobileGeographicInformationService.
ISPRS,VolumeXXXIV,Part2,CommissionII:525-529.
ZhangJianqun,LiangJuanzhu,2003.
ImplementationofMobileSpatialInformationServiceByMMS.
GeomaticsandInformationScienceofWuhanUniversity,28(1):115-119.
WAPForum,2002.
WAP2.
0TechnicalWhitePaper.
http://www.
wapforum.
org/what/WAPWhite_Paper1.
pdf(accessed28Nov.
2003)LiLuqun,LiChengmingandLinZongjian,2002.
InvestigationontheConceptModelofMobileGIS.
ISPRS,Vol.
XXXIV,part4,CommissionIV.
http://www.
isprs.
org/commission4/proceedings/pdfpapers/415.
pdf(accessed18May2003)MaoHaifeng,2004.
DistributedGISforAgricultureBasedonJ2EE.
GeomaticsandInformationScienceofWuhanUniversity,29(2):142-143.
LocationInteroperabilityForum,2002.
MobileLocationProtocolSpecification.
http://www.
openmobilealliance.
org/lifdownload/LIF-TS-101-v3.
0.
0.
zip(accessed18May2003)GongJianya,2001.
ConceptandDevelopmentTrendofSpatialDatabaseManagementSystem.
ScienceofSurveyingandMapping,26(3):4-9.
WeiZhongya,XuSuning,WuLun,2003.
AWAP-basedGeographicInformationMobileService.
CommunicationTechnologyProceedings,ICCT2003.
InternationalConferenceon,Vol2:1455-1460.