A Context-Aware System Architecture for

ASystemArchitectureforContext-AwareMobileComputingWilliamNoahSchilitSubmittedinpartialfulfillmentoftherequirementsforthedegreeofDoctorofPhilosophyintheGraduateSchoolofArtsandSciencesCOLUMBIAUNIVERSITY1995c1995WilliamNoahSchilitAllRightsReservedABSTRACTASystemArchitectureforContext-AwareMobileComputingWilliamNoahSchilitComputerapplicationstraditionallyexpectastaticexecutionenvironment.However,thispreconditionisgenerallynotpossibleformobilesystems,wheretheworldaroundanap-plicationisconstantlychanging.Thisthesisexploreshowtosupportandalsoexploitthedynamicconfigurationsandsocialsettingscharacteristicofmobilesystems.Morespecifi-cally,itadvancesthefollowinggoals:(1)enablingseamlessinteractionacrossdevices;(2)creatingphysicalspacesthatareresponsivetousers;and(3)andbuildingapplicationsthatareawareofthecontextoftheiruse.Examplesofthesegoalsare:continuinginyourofficeaprogramstartedathome;usingaPDAtocontrolsomeoneelse’swindowingUI;automat-icallycancelingphoneforwardinguponreturntoyouroffice;havinganairportoverhead-displayhighlighttheflightinformationviewersarelikelytobeinterestedin;easilylocatingandusingthenearestprinterorfaxmachine;andautomaticallyturningoffaPDA’saudiblee-mailnotificationwheninameeting.Thecontributionofthisthesisisanarchitecturetosupportcontext-awarecom-puting;thatis,applicationadaptationtriggeredbysuchthingsasthelocationofuse,thecollectionofnearbypeople,thepresenceofaccessibledevicesandotherkindsofobjects,aswellaschangestoallthesethingsovertime.Threekeyissuesareaddressed:(1)thein-formationneedsofapplications,(2)whereapplicationsgetvariouspiecesofinformationand(3)howinformationcanbeefficientlydistributed.Adynamicenvironmentcommunicationmodelisintroducedasageneralmech-anismforquicklyandefficientlylearningaboutchangesoccurringintheenvironmentinafaulttolerantmanner.Forpurposesofscalability,multipledynamicenvironmentserversstoreuser,device,and,foreachgeographicregion,contextinformation.Inordertoef-ficientlydisseminateinformationfromthesecomponentstoapplications,adynamiccol-lectionofmulticastgroupsisemployed.ThethesisalsodescribesademonstrationsystembasedontheXeroxPARCTAB,awirelesspalmtopcomputer.ContentsListofFiguresivListofTablesvAcknowledgmentsvi1Introduction11.1ThesisStatement::::::::::::::::::::::::::::::41.2ThesisOverview::::::::::::::::::::::::::::::62AspectsofMobileDistributedSystems82.1SystemModel:::::::::::::::::::::::::::::::82.2SystemDynamics:::::::::::::::::::::::::::::122.2.1CommunicationDynamics:::::::::::::::::::::122.2.2EnvironmentalDynamics:::::::::::::::::::::152.2.3LocationDynamics::::::::::::::::::::::::172.3Context-AwareComputing:::::::::::::::::::::::::192.3.1SomeExamples::::::::::::::::::::::::::202.3.2Context-AwareCycle:::::::::::::::::::::::212.3.3TypesofInformation:::::::::::::::::::::::222.3.4ModelingaSystem::::::::::::::::::::::::232.3.5InformationDissemination::::::::::::::::::::242.3.6ApplicationAdaptation::::::::::::::::::::::252.4ArchitecturalConsiderations::::::::::::::::::::::::272.5Summary::::::::::::::::::::::::::::::::::283RelatedWork303.1MobileComputing:::::::::::::::::::::::::::::303.2UbiquitousComputing:::::::::::::::::::::::::::323.3Location-basedComputing::::::::::::::::::::::::343.4InformationDissemination:::::::::::::::::::::::::35i4DynamicEnvironments374.1Overview:::::::::::::::::::::::::::::::::374.1.1Approach:::::::::::::::::::::::::::::394.1.2DesignIssues:::::::::::::::::::::::::::424.2DataModel::::::::::::::::::::::::::::::::434.2.1DataTypes:::::::::::::::::::::::::::::434.2.2Self-DescribingRepresentation::::::::::::::::::444.2.3AttributeConventions:::::::::::::::::::::::444.3ApplicationProgrammingInterface::::::::::::::::::::464.3.1Binding::::::::::::::::::::::::::::::474.3.2Queries::::::::::::::::::::::::::::::484.3.3Subscriptions:::::::::::::::::::::::::::504.3.4FaultTolerance::::::::::::::::::::::::::514.4InformationDissemination:::::::::::::::::::::::::534.4.1AReliableMulticastDesign::::::::::::::::::::544.4.2BroadcastChannel:::::::::::::::::::::::::554.4.3MultipleMulticastChannels::::::::::::::::::::554.4.4DetectingMultiply-SubscribedQueries::::::::::::::584.4.5DetectingRecurringUpdateQuerySets::::::::::::::604.4.6MulticastSwitchOverCosts:::::::::::::::::::634.4.7LimitingBandwidth::::::::::::::::::::::::644.5Summary::::::::::::::::::::::::::::::::::655Context-AwareComputingArchitecture665.1SystemOrganization::::::::::::::::::::::::::::665.2ComponentInteractions::::::::::::::::::::::::::675.3DeviceAgent:::::::::::::::::::::::::::::::695.4ActiveMapService::::::::::::::::::::::::::::715.4.1ServiceOrganization:::::::::::::::::::::::725.4.2LocatedObjects::::::::::::::::::::::::::735.4.3LocationInformation:::::::::::::::::::::::745.4.4Query&SubscribeOperations::::::::::::::::::815.4.5MoveOperation::::::::::::::::::::::::::825.4.6ActiveMapScaling::::::::::::::::::::::::825.4.7ActiveMapAvailability::::::::::::::::::::::835.5UserAgent:::::::::::::::::::::::::::::::::845.5.1FunctionalDescription:::::::::::::::::::::::855.5.2ExampleofUse::::::::::::::::::::::::::865.5.3