Sentient Computing for Everyone - CiteSeerX

SentientComputingforEveryone

Diego LópezdIepiña(1)and Sai-Lai Lo (2) (1) LaboratoryforCommunicationsEngineering,DepartmentofEngineering,Unive Cambridge,Cambridge,UK (2) AT&TLaboratoriesCambridge,24aTrumpingtonStreet,Cambridge,UK

rsityof

Key words:

Context-AwareComputing,Location-AwareComputing,CORBA,

Abstract:

SentientComputinggivesperceptiontocomputingsystemssot hattheycan detect,interpret and respond tcohanging aspects of user contexts The . location attributeoafuser’scontextisosfpecialinterestbecause itmakeshumancomputerinteractions more natural. In the last few years, several sophisticated indoorlocationtechnologies,whichcantrackuserwhereabouts, havebeen developed.However,theyareyettobewidelyadoptedbecause oftheirhigh costandcomplexitiesindeployment,configurationandmaintenance. This paperdescribesanovelvision-basedsoftwarelocationsyst em,knownas TRIP,whoselow-cost,off-the-shelfhardwarerequirementsa ndeasy deploymentfeaturesovercomeothersystems’limitations. Nevertheless,in orderto fosterthedeploymentof “sentientspaces”thatbring services to users wherevertheyareorabouttomoveto,alocationsystem mustalsobe accompaniedbythemiddlewaretofacilitateuser-boundsoftware service activation,migrationanddeactivation.LocALEaddressesthi sissueby providingaCORBA-basedsolutionthatdealswithheterogeneouso bject lifecycleandlocationcontrol.Somedistributedapplications combining TRIP’sandLocALE’scapabilitiesarepresentedtodemonstrat tehatSentient Computing canbm e adereadily availableforeveryoneandevery where.

1.

Mobility

INTRODUCTION

UbiquitousComputing[16]envisionsphysicalspaces,suchas offices, meetingroomsorhomes,tobeaugmentedwithfullyint egratedcomputing devices.Iat imstomakeservicesprovidedbythesed evicesascommonly 1

2

DiegoLópezdIepiña(1)andSai-LaiLo(2)

availableaeslectricity.WithUbiquitousComputing,perso nalcomputersare nolongerthefocusofattention.Instead,thedevic esinthephysicalspace providetheirservicesunobtrusivelyandmaynotrequire thedirect commandsfrom the user. SentientComputing[5]isourapproachtomakeUbiquitousCo mputinga reality.Itstemsfromthebasicideathattomakec omputerisedservices pervasiveinourlife,thedevicesprovidingsuchservi cesmustbegiven perception,i.e.thecapabilityto seeor hearwhatentitiesarearoundthem; whattheseentitiesaredoing;wheretheyareandw hensomethingis happening.Onlythenitispossiblefor theunderlyingcomputingsystemto undertakesuitableactionstomatchtheenduserexpectat ions.Forexample, whenauserentershisoffice,dependingonthetime anddayothe f week,the sentientenvironmentcouldautomaticallyinitiatethe playbackofaspecific kindofmusic.Iafcolleaguelateroncomesintothe roomtodiscusssome projectideas,themusicvolumecouldbeautomaticallyad justedtofacilitate communication.Inordertodoso,SentientComputingm ustcollectdata fromavarietyofsensorsintheenvironmentandac tuponthesestimuli according tporeviously specified userpreferences. Location-AwareComputing[9],whosebehaviourisdetermi nedbythe positionoof bjectsintheenvironment,representsan interestingsubsetofthe SentientComputingparadigmsincelocationios ftenan essentialattributeof thecontext.Thishasmotivatedthedevelopmentosf e veralindoorlocation systemsfeaturingdifferentlocationgranularity,ran gingfromroom-scale resolutionsuchastheinfrared-basedActiveBadge[15], tothemore accurate3Dresolutionofferedbysystemssuchastheult rasound-based ActiveBat[4]otrheradio-based3D-iD[17].Thesesyst emsrequirepeople orobjectstowearanelectronictagthattransmits auniqueidentifiervia infrared,ultrasoundoradiotoanetworkosensors f onthewallsoceilings. r A LocationServer thenpollsandanalysesthedatafromthesensorsa nd makestheinformationavailabletoapplications.These systemsshareseveral drawbacks.Thetagstheyuseneedbatterypowerandare expensive.The infrastructurerequired,anetworkofsensors,iscompl exandexpensiveto installandmaintain.Thesefactorsmaylimittheir practicaluseoutside researchlaboratories.Wehavedevisedanalternativ esensortechnology, calledTRIP,thatprovidesabettertrade-offbetween thepriceandflexibility ofthetechnologyandtheaccuracyotfhelocationd ataprovided.TRIPisa vision-basedsensortechnologythatrecognisesandl ocatesprinted2D circularbarcode tagsusing inexpensive low-resolution CC Dcameras. InordertopromotetheuseotfheSentientComputingpa radigminour livingspaces,iitsnotsufficienttomakecomputings ystemsawareotfhe user’spresence,movementorpreciselocation,itisi mportant thatthese systemsareprovidedwiththecapabilitytoautomatical lyactivateservices


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onbehalfoftheuserwhentheappropriatecontextualcond Furthermore,itisdesirabletoenableuser-boundservice ashemovesthroughthephysicalspace,andtodeacti whentheuserleavesthespace.Inotherwords,what middlewareinfrastructurethatgivessentientapplicati computingobject’slifecycleandlocationinanetwork frameworkios urmiddlewaresolutiontothisneed.Se theTRIPtechnologyandthedistributedsysteminfras it.LocALEisintroducedinsection4Section . 5descr combiningTRIPandLocALE.Section6summarizessomer Thisifsollowed btyhe conclusionsisnection 7.

2.

itionsaremet. stofollowtheuser vatesuchservices isneededisa onsthecontrolovera .TheLocALE ctions2and3explore tructurebuiltontopof ibessomeapplications elatedresearch.

TRIP: A DOWNLOADABLELOCATIONSENSOR

TRIP(TargetRecognitionusingImageProcessing)[8] isanovelvisionbasedsensorsystemthatusesacombinationofvisualm arkers(2-D ringcodes)andconventionalvideocamerastoidentifytagged objectsinthe fieldofview.RelativelylowCPUdemandingimagepr ocessingand computervisionalgorithmsareappliedtovideoframes toobtainthe identifier( TRIPcode)andpose(3Dlocationandorientation)otfhetarge ts relative ttohe viewing camera. even-parity sectors

1

syncsector

0

2

* 102011221210001 Figure 1.TRIPcoderepresenting number1,160,407

TRIPconstitutesaverycheapandversatilesensorte ringcodesareprintable,andcanthereforebaettached suchabs ooksooffice r stationeries(e.g.stapler).A readincounter-clockwisefashionfromitssynchroni

chnology.Its2-D eventolow-costitems, TRIPcode(seeFigure1), sationsector,represents

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13 aternarynumberintherange1-3 (1,594,323).Onlyoff-the-shelfhardware isrequired,i.e.low-resolution CCDcamerasand CPU processing power. TheTRIPsoftwarewillbemadepubliclydownloadablein duecourse. Userswithaweb-camattachedtotheirPCscaneasi lyinstallandrunthis software sensorand hence provide visual awarenessto theircomputers. Whenthe TargetRecognitionAlgorithm isappliedtotheimages,asetof imageprocessingstagesisexecutedinordertodeterm inetheidentitiesand positions(x-ycoordinatesintheimage)whereTRIPco desarespotted.[8] fullydescribesthemathematicsinvolved.Inaddition ,aPoseExtraction Algorithmisemployed.Givenasingleviewofatarg et,thismethod , , t)hat determinesthetranslationvector(t tx, yt, za) ndrotationangles( definetherigidbodytransformationbetweenthecame racoordinatesystem andthetarget-centredcoordinatesystem.Themetho dappliedibs asedonthe POSE_FROM_CIRCLEmethod given i[n3]. TheC++implementationoftheTargetRecognitionAlg orithmprocesses 15640x480pixelsframespersecondonan800MHzPentiumIII.When the targetrecognitionandposeestimationaresimultaneo uslyundertaken,the performanceachievedisabout12Hz.TRIPcodesarerecogn isedaslongas thetarget’splaneorientationanglesarelessthan 70ºanditsimageoccupies atleast20x20pixels.The3Dlocationothe f centreoatf argetrelativetothe viewingcameraisobtainedwithlessthan5%error.A nevenerrorparity check (see Figure 1isu) sed tporeventthe identificat ion ofalse f positives.

3.

TRIP: A DISTRIBUTED

SENSORSYSTEM

Anevent-baseddistributedarchitecturehasbeendevised aroundTRIPin ordertomanipulateanddistributethesensordataprovi dedbythis technology.ThefunctionalityoftheTRIPsystem,i. e.itstargetrecognition andposeextraction,hasbeenencapsulatedbyaCORBA[11] component, named TRIParser.ThiscomponentoffersaUNIX pipe-likeinterfacethat enablesapplicationstoconnectdistributed FrameGrabber components, whichsupply imagesfromcameras,toTRIParsers.ATRIParsermay consumeimagessuppliedbyoneomore r FrameGrabbers TRIP . processing resultsare,bydefault,asynchronouslycommunicatedin anevent-formtoa CORBA NotificationChannel [10], whichis associated with each TRIParser.TheNotificationChannelservesasadecouplerbetweenthe frame analysersand the componentsinterested itnhe results. ATRIParserpushes TRIPevents(seeFigure2)toitsassociated NotificationChannel.Thepartiesinterestedinagi venTRIParser’slocation datasubscribetoitsassociatedchannelandconveya setofconstraintsthat specifytheeventstheyareinterestedinreceiving. TheNotificationChannel


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undertakesconsumerregistration,eventfilteringand communicationon behalfofitsrepresentingTRIParser.Thefiltercons traintlanguagesupported istheconstraintlanguagedefinedbytheOMGTrading Service.Hierarchical interconnectionsoftheseNotificationChannelscan becreatedinorderto ensuretheefficientandscalabledisseminationotfh eTRIParseroutput.The TRIParseralsoprovidesasynchronousinvocationinte rface( processFrame) thatanalysesasubmittedframeandreturnsthelocati ondatainferredfrom it. Hence,applicationscaninteractwithaTRIParsereit her synchronouslyor asynchronously.However,forefficiencypurposes,anappl icationshould establishdirectcommunicationbetweena FrameGrabber andaTRIParser, and registerasaenventconsumerto the parser’sNot ification Channel. struct TRIPevent { string TRIPcode; // code ternary representation string cameraID; // capturing camera identifier paramsEllipse params; // bull’s-eye’s outer ellipse parameters (x,y,a,b, θ) targetPosition pose; // translation vector from camera origin to target centre targetOrientation angels; // ( , , ) };

Figure 2.TRIPeventcontents

3.1

TheTRIPDirectoryServer

ATRIPDirectoryServer(TDS)hasbeencreatedwith thepurposeof regulatingtheTRIPcodegrantingprocessandestablish ingmappings betweenreal-worldobjectsandTRIPcodes.Thiscompone ntensuresthe efficientutilisationotfheTRIPcodeaddressspacea nditsclassificationinto categories.TheTDSoffersCORBAinterfacesforthe creation,modification, deletion and retrieval ofboth TRIPcodesand theirc ategories.

3.2

TheSentientInformation Framework

TheSentientInformationFramework(SIF)definesan application constructionmodeltostreamlinesentientapplication development.SIF isolatescontextcaptureandabstractionfromapplication semantics.Athe sametime,ipt rovidesefficientmechanismsforcont extcommunication.Its mainfunctionitsotransformcontextinformationint otheformatsdemanded bytheapplications.SIFisnotconstrainedtoTRIPsi nceitissensortechnologyindependent.Inthisframework,component sarecategorisedinto 3types(seeFigure3):(1) ContextGenerators (CGs),(2) ContextChannels (CCs)and(3) ContextAbstractors (CAs). ContextGenerators encapsulate

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sensors,suchaT s RIP,andthesoftwarethatextracts informationfrom them. Theyaresourcesofsensorialevents. ContextChannels ,inourcase implementedasCORBANotificationChannels,receive eventsand,after consumerspecifiedfiltering,passtheeventstothec onsumers. Context Abstractors achievetheseparationocf oncernsbetweencontextsen singand applicationsemantics.Theyconsumetherawsentientd ataprovidedbyCGs (e.g.TRIPcode1234spotted),interpretitscontents(e.g user . Diegospotted) andaugmentit(e.g.Diego’sloginids ipina)toproduc enhancedcontextual eventsthatcanbedirectlyusedbyapplications.Theyc analso correlate otherCAs’oC r Gs’outcomestogeneratetherequired sentientdata.Fora more detailed description oSIF f referto [6]. Context Generator 1

Context Generator 3

Context Generator 2

push events CG3

push events CG2

push events CG1

Context Channel B

Context Channel A

push filtered events


Context Abstractor 1 push events CA1

Application 1


push events CA2

Context Channel C push filtered events

Context Abstractor 2

Context Channel D

pull filtered events

Application 2

Application 3

Figure 3.TheSIFArchitecture

4.

LOCALE:MIDDLEWAREFOROBJECT LIFECYCLE ANDLOCATIONCONTROL

Inordertomakesentientcomputingavailableforever yoneand everywhere,wehave,sofar,describedanewcost-ef fectiveandeasily deployablelocationsensortechnology,TRIP,andase ntientapplication constructionmodel,SIF,fortheefficientmanipulatio nanddisseminationof sensorialdata.However,onequestionstillhastobe answered,i.e.oncea sentientsystemreceivesahighlevelevent(e.g.D iegoentershisoffice),how canthesystemeffectivelytriggertherequiredacti on,i.e.activates, deactivatesomigrates r user-bound a software service?


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Ourexperiencewithsentientapplicationdevelopmenthas pointedusto theneedforaninfrastructuretostreamlinethelife cyclecontrolofuserassociatedservices.Otherwise,everytimeanewse ntientapplicationis developed,thedistributedcomponentsinvolvedinitso perationhavetobe manually started. This makes sentient application deplo yment very cumbersome.Moreover,user-relatedservicesareoften boundtouser locations,e.g.theactivationoaf nMP3playermustt akeplaceinoneotfhe PCsinaroomwhereauserpresenceids etected.Ther efore,itisdesirableto controlboththelifecycleandlocationofuser-bounds ervicesbya middleware designed forthispurpose. TheLocALE(Location-AwareLifecycleEnvironment) framework[7] definesasimplemechanismformanagingthelifecycl eandlocationof distributedCORBAobjectsresidingonanetwork.Inad dition,ipt rovides load-balancingandfault-tolerancefeaturestotheobje ctswhoselifecycleit manages.Theemphasisofitsdesignisplacedonprovi dingasuitable interfaceforthirdparty object-locationcontrollers T . hesecontrollerscan intelligentlydirectwhenandwherecomponentsarea ctivatedormoved basedontheinputsonuserwhereaboutsandthelocation, loadand capabilitiesofcomputingresources.LocALEoffersanobj ect-lifecycle infrastructure,simplifyingsentientapplicationdeployme ntand enabling CPUintensivesystems,suchaT s RIP,toreusethespar reesourcesavailable in network. a

4.1

LocALEArchitecture

TheLocALEmiddlewarehas3½-tier a architecture(Fig ure4).Itconsists ofclientapplicationsand the following 3typesocom f ponents: – The LifecycleManager (LCManager)providesobject-typeindependent lifecyclecontrolinterfacesandmediatesthelifec ycleoperationsoverany CORBAobjectresidinginalocationdomain.Alocati ondomainisa groupofmachinesonaLANthatarephysicallylocated inthesame place,suchasabuilding,afloororaroom.Everyobje ctcreation, movementordeletionrequestisroutedthroughthisco mponent.This permitstheLCManagertocachethecurrentlocationo efveryobjectina domainandthusactasa forwardingagentthatredirectsclientrequests afterobjectreferencesheldbyclientsarebrokendue toeitherobject movementofrailure.Inthelattercase,theLCManag ertriestorecover the failed object,and,in case osuccess, f returnsth neew objectreference. – LifecycleServer(s) (LCServer)arecontainersoLocALE-enabled f objects thataresubjectedtolifecyclecontrol.Lifecycleope rationsinvokedonan LCManageraredelegatedtosuitableLCServers.Theys ubsumestandard stronglytypedfactoryfunctionalitiesbyprovidinga typespecific

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creationmethodwithhard-codedtypes.Furthermore,t heyalsoassist theirlocalobjectsontheirmigrationtootherLCSe rvers.Theycanbe startedeithermanuallyorbythelocalLCManageraft eracreationor migrationrequestarrivesaaltocationwherethere quiredLCServertype doesnotexist.Ineithercase,theyregisterwitht hemanagerbypassing ontheirphysicallocation(host),theirCORBAobject reference(orIOR) and dataspecificttohe type oobjects f they handle. – Type-specificProxyFactories areplacedinbetweenclientsand LCManagers.Theysaveclientapplicationsfromdealin gwiththegeneric objectcreationinterfaceofferedbyanLCManager.Us ingtype-specific interfacesmakesclientcodefarshorterandsimpler tounderstand.With thegenericversion,iafmismatchinthetypeoaf constructorargument occurs,theclientwouldonlyreceiveanerrorartuntimeratherthanat compiletime. Type-specificProxyFactories offertypespecificobjectcreationmethodswiththesameargumenttypesandsem anticsasthe LCServerstheyrepresent.Theymaptypespecificrequest tsothegeneric formatdemandedbyLCManagers.Theyareondemandac tivatedbythe local LCManager. Type A Proxy Factory strongly-typed creation requests LocALE Client 1

… Type X Proxy Factory

… LocALE Client N

Tier 1

generic creation requests

Lifecycle Manager migration, removal & redirection requests

Type A Server lifecycle Lifecycle at Host 1 operations delegation

…

Type A Lifecycle Server at Host N

…

Type X Lifecycle Server at Host 1

…

Tier 2

…

Type X Lifecycle Server at Host N

Tier 3

Figure 4. LocALE3½-tierarchitecture

TheLocALEarchitectureguaranteescompile-timetypesa fetyofclients withrespecttothelifecyclecontroloftheirservi ces.Clientsfind,through theLCManager,objectreferencestotype-specificproxy factoriesandissue throughthemobjectcreationrequests.Objectmigration anddeletion requestsaredirectlyinvokedontheLCManagerbecause theyareobjecttype independent.TheLCManagerthendelegatesincomingl ifecycleoperations to the appropriate LCServers.


4.2

9

Location-constrained LifecycleControl

OneofthemainadvantagesofCORBA[11]isthatiot fferslocation transparencytoapplications,i.e.im t akesmethodinv ocationsas impleon remoteobjectsaos nlocalobjects.LocALEleverages onCORBA’slocation transparencybutiitsabletocontrol whereservicesarelocated.Itcanalso settheconstraintsunderwhichtheseservicescanl aterbere-located.We thinkthesefunctionsmaybringimportantbenefits.For example,loadbalancing systemsmaywishtoinitiatenewserviceinstances onthehostsof thesameLANwiththelowestprocessingload.Follow -mesentient applicationsmaywanttomoveobjectstiedtoauser’s physicallocationto thenearesthostwiththerequiredcapabilities.LocAL Eallowsapplications tocontrolthelocationofCORBAobjects.Itextends conventionalobject factorieswithadditionaldistributedobjectconstructi onsemantics.The followingtwoattributesareappendedtotheobjectcrea tioninterfaces offered btyhe proxy factories: – Locationattribute( LocSpec):specifies “where”aserviceshouldbe instantiated (or moved to). The formats available fo r location specificationare:(1) hostDN(hostName),(2) roomID(room)and(3) hostGroup(listHostName). hostDNand roomIDareusedwhenthe applicationwantstocreateanobjectonaspecifichos ot irnaspecific room.Bysetting hostNameor roomattribute to “ANY”in eitherotfhese LocSpecsthe , programmercaninstantiatelocation-independent services. The hostGroupformatisusefultospecifyanarbitrarysetofhosts where an objectmay bcereated,e.g.hostsiroom an with a udio capabilities. – LifeCyclecontraints ( LCconstraintsa) ttribute:determineswhetherthe objectcreatedshouldbeconsideredas RECOVERABLEand/or MOVABLE withinthelocationscopeinwhichiis tcreated,i. e.onahost,inaroom orahostgroup.Arecoverableobjectiseitherastate lessoapersistent r objectwhose state can breestored afterfailure. Withrespecttotheabilitytocreateobjectsbasedon thelocation constraintssupplied,theLCManagerprovidesasimilar functionasa conventionalTrader.TheLCManagermatchescliento bjectcreation specificationsagainsttheregisteredobjectLifecycl eServertypesand locations,and delegatesthe operation tsuitable ao L CServer.

4.3

LocALEImplementation

TheLCManagerhasbeenimplementedinC++usingtheCO C++ORBomniORB[1].Itsimplementationmakesextensiv advancedfeaturesprovidedbytheCORBA2.3’sPortableObj (POA).Amongthese,irteliesonthePOAdefinedst

RBA2.3 euseosf ome ectAdapter andardmechanismto

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generateLOCATION_FORWARDreplymessages.Thesemessa gesaresent byLCManagerstoclientORBstoindicatethenewloc ationofanobject wherepreviouslyissuedrequestshavetoberedirected. Adetailed descriptionontheimplementationotfheLocALEmiddl ewareias vailablein [7].

5.

TRIP-ENABLEDSENTIENT APPLICATIONS

Thissectiondescribesthreesentientapplications sensingwithLocALE’sobjectlifecycleandlocation demonstratehowourworkstreamlinesthedeploymento and make icatost-effective process.

5.1

1

thatcombineTRIP management.They fsentientsystems

TheLCESentientLibrary

Thissystemaugmentsaconventionallibrarycatalogue systemwith sentientfeatures.Apartfromthetypicalfunctionaliti esexpectedinabook cataloguingsystem,theLCESentientLibraryoffersc ontextualinformation aboutthebooksinourlab.Detailsonthelastseenbook locationandits proximitytootherfixeditemsintheenvironmentare offered.This applicationisanillustrationofTRIP’sversatilityf ortrackinganytag-able entitiesitnhe environment.

Figure 5.LCESentientLibrary snapshot

Everylocationwhereabookmaybelocatedinourlabh witha location-categoryTRIPcode.Similarly, havebeenattachedtobookspines.Periodically,theL 1 The firsttwo applicationsareavailableat:

asbeentagged book-categoryTRIPcodes CElibrarianwanders

http://www-lce.eng.cam.ac.uk/~dl231/#Demos.

SentientComputingforEveryone aroundourlabwithavideocamerarecordingTRIPtagg books.Thesystemautomaticallyupdatesthebookdatabase processingofthebook-sightingvideo.Thisprocessi operationofaVideoFrameGrabber,whichprovidesacce frames,aTRIParser,whichanalysesthoseframes,a Server,wherebookdetailsandcontextualdataarerec FrameGrabberandTRIParsercomponentsareautomaticall LocALE. AwebinterfaceallowsLCEmembersto(1)browseallth categories,(2)listbooksinacategory,(3)obtainboo performkeyword-basedsearchobf ooks.Figure5showsth search with thiswebinterface.

5.2

11 edlocationsand bytheoff-line nvolvesthecosstothevideo nd theTRIPDirectory orded.TheVideo yactivatedby ebook kdetailsand(4) reesultofabook

ActiveTRIPboard

Figure 6.ActiveTRIPboardsnapshot

Thisapplicationaugmentsaconventionalwhiteboardwit hinteractive commandsissuedbyplacingTRIPcodesinthefieldofv iewofacamera pointingathewhiteboard.Someexampleactionsthatc anbetriggeredare: (1)capturewhiteboardsnapshotandemailitsweblinkto peoplecurrently presentintheroom,(2)printoutacopyotfhewhiteboar dsnapshotforeach personintheroom. Theapplicationcomponents:aFram eGrabberanda TRIParserareactivatedviaLocALEeitherwhenaper sonappearsinthe meetingroomorthroughawebinterface(seeFigure6). TheActiveBadge indoorlocationsystemdeployedinourlabisusedtod etermineperson presence.Infuture,themeetingroomwillbepopulatedwi thsufficient camerastocoverallthefieldofviewsoftheroom a, ndsopermitpeople

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wearingTRIPcodetagstobedetected.ThroughLocALE, activatedinaload-balancingwaybyrandomlypicking candidatelist.ItfheTRIParserfails,theapplicati becauseLocALE’sfault-tolerancesupportwillrecreateth the available host.

5.4

theTRIParser is oneotfhehostsina onrecoverstransparently eparserononeof

Follow-meAudio

Thisapplication providesmobileuserswithmusicfromthenearest speakers wherevertheyare. Thesourceom f usicisanMP3jukeboxserver whoseoperationiscontrolledbyshowingjukebox-typeTR IPcodestowebcamsattachedtosomeofourlab’sPCs.Apersonalsof twareagent, associatedwitheachlabperson,listensforthatpers on’smovementevents generatedbya PersonLocationMonitorContextAbstractor .This componentobtainspeoplesightingsfromthe ContextChannels ofthe TRIParserscorrespondingtothePCweb-camsspreadth roughoutthe laboratory.FromrawTRIPsightingevents,itgenera tespersonnelpresence andmovementevents.Thepersonalagent,actingasa componentmigration controller,requestsLocALEtomigratetheaudioplaye ar ndMP3decoder componentstothehostnearesttotheuserthatcand eliverthemusic.Asthe userwandersaroundthelocation-awarecomputingenviro nment,themusic followshim.Thestateofthesystemandtimeindex intothecurrentsong persistsasthecomponentsmigrate.Thisapplication makesuseoT f RIP’s trackingcapabilities,SIF’scontextmodellingfeatures andLocALE’s migration support.

6.

RELATED WORK

SONY’sCyberCode[12]isvisual a taggingsystem basedo barcodethatcanbeusedtodeterminethe3Dpositionan taggedobjects.Severalaugmentedrealityapplications basedonthissystem,e.g.thevisitorviewofCyberC museumisaugmentedwithsynthesisedinformation.The ofCyberCodesrequirehigherimageresolutionforthei andlocationthanTRIP.BBC’sfree-d[14]locationsy precisepositionandorientationofstudiocameras,by cameramountedonthebackofaconventionalmovingc circularmarkers,similartoTRIPcodes,placedonthe recordingstudio.Ahardwareimplementationofitsal necessarytoachieverealtimeprocessing.Thesyste reality TV production.Itisexpensive and cumbersome to

2D na square didentifierof havebeenproduced odetaggeditemsina geometricfeatures ar ccuraterecognition stemmeasuresthe usinganauxiliary amerapointingto ceilingofaTV gorithmswas misusedforvirtual deploy.


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GeorgiaTech’sContextArchitectureproject[2]attempts tomakesentient applicationdevelopmentassimpleasGUIdevelopment.Fo rthatit introducesContextWidgetsthatseparatecontextsensin gfromcontext-use. IthassomesimilaritiestoSIFbutdoesn’ttackleef ficientcontext informationdissemination.Microsoft’sEasyLiving[ 13]projecttriesto createreactivecontext-awarelivingspaceswithoutth euserhavingtowear anylocationtagocomputing r device.Theirapproachtr ackspeoplebasedon colourhistogramswithoutrequiringtheusertowearan ymarker.Thishasa muchheaviercomputationaldemandandproduceslessreli ableresultsthan TRIP.AT&T’sSentientComputingproject[5]aimstorepl acehumancomputerdirectinteraction(throughmouseokr eyboard) byenablingusers toinsteadinteractwiththeirsurroundingspacebased onthepreciselocation andorientationprovidedbytheActiveBatLocationS ystem[4].This concepthasbeen explored with several sophisticated sen tientapplications.

7.

CONCLUSION

TRIP,anovelcost-effectiveandeasilydeployablelo cationsensor technology,hasbeenintroduced.Thissensorrequires onlyinexpensiveand off-the-shelfhardware,whichmakesthecreationof location-awarereactive environments,eveninthehome,anaffordableproposit ion.Allthatis requiredtoaugmentastandardPCwithvisualawarenes isasweb-camand TRIP’sdownloadable software. SIF,anapplicationconstructionmodeltoeasethedev elopmentof distributed sensor-driven systemshasalso been descri bed. LocALE,anobjectlifecycleandlocationcontrolmid dlewarethat streamlinesuser-boundserviceactivation,migrationa nddeactivationand,at thesametime,permitsapplicationdeveloperstoreuset hesparenetworked computingresourcesinaLAN,hasbeenpresented.LocALE complements TRIP’sminimalcostanddeploymentcomplexity.Itisa veryusefultoolfor sentientapplicationsthathavetotriggeruser-relate dservicesinresponseto captured sensordata. To validate our contributions, several TRIP-enabled appli cations, followingtheSIFmodelandleveragingontheLocAL Einfrastructurehave beendevelopedanddescribedinthispaper.Theinitial resultsare encouraging.

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ACKNOWLEDGEMENTS DiegoLópezdeIpiñaisverygratefultotheBasqueGov DepartmentofEducationforthesponsorshipohf isPhD also due tA o T&TLaboratoriesCambridge forsponsoring

ernment’s studies.Thanksare the TRIPproject.

REFERENCES [1] AT&TLaboratoriesCambridge,“omniORBC++CORBA ORB” , http://www.uk.research.att.com/omniORB/omniORB.html [2]DeyA.K.,SalberD.,FutakawaMand . AbowdG“An . archite cturetosupportcontextawareapplications”,12thACM’sUIST,1999 [3]ForsythD.,MundyJ.L.,ZissermanA., CoelhoC.,HellerA.andRothwellC.“Invariant Descriptorsfor3-DObjectRecognition and Pose”, IEEE Tr ansactions on Pattern Analysis andMachineIntelligence,Vol.13,No.10,pp.971-991,October1991 [4]HarterA.,HopperA.,StegglesP.,WardAand . WebsterP.“TheAnatomy oC af ontextAwareApplication”,ProceedingsoMOBICOM’99, f August1999 [5]Hopper.A.“SentientComputing”,TheRoyalSocietyCliff ordPatersonLecture,AT&T LaboratoriesCambridge,TechnicalReport1999.12,1999 [6]LópezdeIpiña,D". BuildingComponentsforaDistributedSenti entFrameworkwith PythonandCORBA ", Proceedingsotfhe8thInternationalPythonConference,January 24 27, - 2000 [7]López deIpiña,Da. ndLoS."LocALE:aLocation-AwareLifecyc leEnvironmentfor UbiquitousComputing", ProceedingsoICOIN-15, f February 2001 [8]LópezdIepiñaD.,”TRIP: A Distributedvision-basedSensor System”,TechnicalReport, Laboratory forCommunicationEngineering,Cambridge,September 1999 [9]NelsonG.“Context-AwareandLocationSystems”.PhDThes is.CambridgeUniversity ComputerLab,UK,January 1998 [10] ObjectManagementGroup.“NotificationServiceSpecific ation”,June2000 [11]ObjectManagementGroup.“TheCommonObjectRequestBroker Architecture: ArchitectureandSpecification”,October1999 [12]RekimotoJand . AyatsukaY“CyberCode: . Designing Augmented Reality Environments withVisualTags”,Designing AugmentedReality Environments( DARE2000),2000 [13] ShaferS,etal.“ThenewEasyLiving ProjectatMicr osoftResearch,Microsoft,1999 [14]ThomasGA., . JinJ.,NiblettT.,UrquhartC.“A versa tilecamera positionmeasurement system forvirtualreality inTVproduction”,Proceedingso IBC’97, f September1997 [15]WantR.,HopperA.,FalcãoAand . GibbonsJ“The . Active BadgeLocationSystem”, ACMTransactionsonInformationSystems,Vol.10,No.1.91102, January 1992 st [16] WeiserM.“TheComputerforthe21 Century”. Scientific American,September1992 [17]WerbJ.andLanzlC“. Designingapositioningsystemfor findingthingsandpeople indoors”,IEEESpectrum,pp.71-78,September1998