Internet of Things: A Context-Awareness Perspective · Internet of Things: A Context-Awareness...
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Chapter 13
Internet of Things: A Context-Awareness Perspective
Davy Preuveneers and Yolande Berbers
Contents13.1 Introduction......................................................................................288
13.1.1 SoftwareArchitectureandtheInternetofThings.....................28813.1.2 ContextAwarenessandtheInternetofThings...........................28913.1.3 ConvergenceasaKeyEnablerfortheInternetofThings...........290
13.2 State-of-the-ArtonContext-AwareComputingforNonintrusiveBehavior.......................................................................29013.2.1 ADefinitionofContext.............................................................29113.2.2 UsingRFIDtoSenseContext....................................................29113.2.3 RequirementsforRepresentingandExchangingContext..........292
13.3 TrendsinContext-AwareComputingwithinServiceOrientation..........29613.3.1 Context-EnabledServiceOrientedArchitecture
andtheSemanticWeb................................................................29613.3.2 Context-EnabledServiceDeliveryPlatforms..............................297
13.4 ServiceProvisioninaContext-Aware,ConvergedServiceArchitecture............................................................................................29913.4.1 ContextManagementasanEnablingService...........................30013.4.2 ConveyingContextandDistributedStorage..............................301
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13.1 IntroductionThenextwaveintheeraofcomputingwillbeoutsidetherealmofthetraditionaldesktop.IntheInternetofThings�paradigm(IoT)[22],everythingofvaluewillbeonthenetworkinoneformoranother.RadiofrequencyIDentification(RFID)andsensornetworktechnologieswillgiverisetothisnewstandard,inwhichinfor-mation and communication are invisibly embedded in the environment aroundus.Everydayobjects, suchascars,coffeecups, refrigerators,bathtubs,andmoreadvanced,looselycoupled,computationalandinformationserviceswillbeineachothersinteractionrangeandwillcommunicatewithoneanother.Largeamountsofdatawillcirculateinordertocreatesmartandproactiveenvironmentsthatwillsig-nificantlyenhanceboththeworkandleisureexperiencesofpeople.Smartinteract-ingobjectsthatadapttothecurrentsituationwithoutanyhumaninvolvementwillbecomethenextlogicalsteptopeoplealreadyconnectedanytimeandanywhere.WiththegrowingpresenceofWiFiand3GwirelessInternetaccess,theevolutiontoward ubiquitous information and communication networks is already evidentnowadays.However,fortheInternetofThingsvisiontosuccessfullyemerge,thecomputingcriterionwillneedtogobeyondtraditionalmobilecomputingscenariosthatusesmartphonesandportables,andevolveintoconnectingeverydayexistingobjectsandembeddingintelligenceintoourenvironment.Fortechnologytodis-appearfromtheconsciousnessoftheuser,theInternetofThingsdemands:(1)asharedunderstandingofthesituationofitsusersandtheirappliances,(2)softwarearchitectures andpervasive communicationnetworks toprocess and convey thecontextualinformationtowhereitisrelevant,and(3)thecomputationalartifactsintheInternetofThingsthataimforautonomousandsmartbehavior.Withthesethreefundamentalgroundsinplace,smartconnectivityandcontext-awarecompu-tationviaanything,anywhere,andanytimecanbeaccomplished.
13.1.1 Software Architecture and the Internet of ThingsAnysoftwarearchitecture,designedtobedeployedwithinthesettingoftheInter-net of Things, will need to foresee the increasing heterogeneity of devices andnetworks,andwillhavetoprovideforvaryinguserandapplicationrequirementswithindiversecontextsofserviceprovision.Itwillbeessentialfornewarchitectures
�Internet of Things refers to a ubiquitous network society in which a lot of objects are“connected.”
13.5 ContextAwarenessfromRFIDtotheEnd-UserintheInternetofThings.........................................................................303
13.6 Conclusions.......................................................................................30413.7 OpenIssues............................................................................................305References.........................................................................................................305
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tointegratethelatesttechnologiesintheareasofsoftwareandhardwareinordertoassimilateasmuchaspossibledataandservicesavailableintheenvironmentoftheuser.Asserviceintegration-relatedtaskswillremaininevitable,itisnosurprisethattheindustryisaimingforsoftwaresolutionsthatmakethisintegrationamoretrac-tableactivity.Theevolutiontowardintegratedserviceorientationisalreadyemerg-ingintheongoingconvergenceofWebservicesandtelecommunicationservices[21].Service-OrientedArchitecture(SOA)[27]isanarchitecturalstylethatenablesthecomposition of applications by using loosely coupled and interoperable services.Theseoftentransaction-basedservicesaredescribedandexposedusingopenstan-dards—inthecaseofWebservicesusingWSDL,SOAP,andBPEL[40]—thatareindependentoftheunderlyingprogramminglanguageandplatform.Thetelecom-municationsworldhasembracedtheServiceDeliveryPlatform(SDP)architecturalapproachtoenablemoreflexiblecommunicationandcollaborationservicesbyevolv-ingtoall-IP(InternetProtocol)networksforthedeliveryofmultimedia-enabledandlocation-orpresence-awareservices.Duetoitsevent-drivencommunicationpara-digm,anSDPdiffersfromthepreviousarchitecturalstyleinthataSOAtypicallydoesnotneedtomeetanyreal-timedemandsforitsdata-drivencommunication.BothSOAandSDPsoftwarearchitecturescommonlyprovisionserviceorchestra-tioncapabilitiesbyexposing their servicesusingopen standards, andoften sharebuildingblockstohandlenoncorefunctionalities,suchasauthentication,identitymanagement,andbilling.Asaresult,convergedservicesbringustheflexibleinterac-tionsfromtheWebserviceparadigm,nicelyintegratedwiththecommunicationandcollaborationservicesfromthetelecommunicationsworld.KeytothesuccessoftheInternetofThingswillbetheabilitytoconnecteverydayobjects,includingRFIDtagsandotherexistingresources,tosuchservice-orientedarchitecturessothatitwillleadtoanoverallflexiblearchitecturethataimstocreateapleasantuserexperienceattheworkplace,inpublicareasaswellasinthehomeenvironment.
13.1.2 Context Awareness and the Internet of ThingsContextawarenessplaysanimportantroleintheaforementionedsoftwarearchi-tectures toenableservicescustomizationaccordingtothecurrentsituationwithminimalhumanintervention.Acquiring,analyzing,andinterpretingrelevantcon-textinformation[11]regardingtheuserwillbeakeyingredienttocreateawholenewrangeofsmartentertainmentandbusinessapplicationsthataremoresupport-ivetotheuser.Althoughcontext-awaresystemshavebeenintheresearchepicenterformorethanadecade[32,33],theabilitytoconveyandselectthemostappropri-ate information toachievenonintrusivebehavioronmultiuser-convergedserviceplatformsinmobileandheterogeneousenvironmentsremainsasignificantman-agementchallenge.InteroperabilityatthescaleoftheInternetofThingsshouldgobeyondsyntacticalinterfacesandrequiresthesharingofcommonsemanticsacrossallsoftwarearchitectures.Italsodemandsaseamlessintegrationofexistingcom-putationalartifacts(hardwareandsoftware)andcommunicationinfrastructures.
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Onlythencancontextinformationbesuccessfullysharedbetweenhighlyadaptiveservices across heterogeneous devices on large-scale networks that consider thisinformationrelevantfortheirpurposes.
13.1.3 Convergence as a Key Enabler for the Internet of Things
Insummary,theInternetofThingsisallaboutconvergence,fromconnectedcom-puting using RFID and sensor technology to digital content and context-awareservices,anobservationthatwasalsomadeinthedigital lifestylechapterofthedigital.life ITU Internet Report 2006[23].ThesuccessoftheInternetofThingswillnotsomuchdependonthedevelopmentofnewtechnologies,butmoresooncon-nectingandintegratingexistingresources,rangingfromsmall-scaleobjects,suchasRFIDtags,uptolarge-scalesoftwaresystemsthatservethousandsofclientsatatime.Thegoalistocreateasoftwarearchitecturethatenablesobjectstoexchangeinformation through the Internet to achievenonintrusivebehavior and custom-izedservices.Partofthearchitecture’sresponsibilityistomakesurethatrelevantinformationarrivesattherightplaceinawaythattherecipientunderstandswhatitreceives.Here,weinvestigatehowsuchanarchitecturecanbedesignedbyinte-gratinginnovativescientificresultsfromrelatedresearchdomainswithindustrialtechnologiesandpracticeswithaproventrackrecord.
In section 13.2, we describe the current state-of-the-art in context-awarecomputinganddiscuss thegoals,motivation, and requirements thatdefine theactualneedforcontextawareness inorder toachieveabetterunderstandingofthe concepts involved. We review the trends for its use in converging service-oriented architectures in section 13.3. To illustrate the benefits of introducingcontext awareness as one of the underpinning fundamentals of the Internet ofThings,wealsoelaborateonourrecentresearchactivitiesatthearchitecturallevelinsection13.4.Itillustrateshowtointegrateexistingtechnologiesandcomputa-tionalartifactssupportingcontextawarenessasanenablingserviceamongstotherbuildingblocksinanoverallservice-orientedarchitectureforuseinhomeappli-ances and online consumer services. By not reinventing the wheel, but insteadleveraging on solid foundations from the software and knowledge engineeringdomains, nothing stands in the way for applications targeting the Internet ofThingsmodeltobecomeasuccess.
13.2 State-of-the-Art on Context-Aware Computing for Nonintrusive Behavior
Thenotionofcontextiswidelyunderstoodinthepervasiveandubiquitouscom-putingdomainasrelevantinformationreferringtothesituationandcircumstancesinwhichacomputationalartifactisembedded.Assuch,contextawarenessisthe
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abilitytodetectandrespondtocontextualchanges.Thegoalofcontext-awarecom-putingistogatherandutilizeinformationtopositivelyaffecttheprovisioningofservices thatareconsideredappropriate foraparticularpersonordevice.There-fore,contextinformationcanonlybeconsideredusefulifitcanbeinterpreted.Ascontextisarathervagueconcept,wefirstmentionhowcontexthasbeendefinedbyleadingexperts inthefieldbeforecontinuingtodescribehowcontextcanbemodeled,acquired,andusedtoachieveautonomousandnonintrusivebehaviorinaservice-orientedarchitecture.
13.2.1 A Definition of ContextManyauthorsinitiallydefinedcontextinformationbyenumeratingtypesofinfor-mationrelatedtotheuserorapplicationenvironmentthatseemedrelevant.ThetermcontextwasfirstusedbySchilitandTheimer[32]toreferto“location,identi-tiesofnearbypeopleandobjects,andchangestotheseobjects.”Brown,Bovey,andChen[6]havedefinedcontextas“location,identitiesofthepeoplearoundtheuser,thetimeofday,season,temperature,etc.”Ryan,Pascoe,andMorse[31]referredtocontextas“theuser’slocation,environment,identity,andtime.”Dey[10]listed“theuser’semotionalstate,focusofattention,locationandorientation,dateandtime,objectsandpeopleintheuser’senvironment”aselementsbeingpartofthedefinitionofcontext.Astheuseofenumerationstodescribecontextwastoolim-ited to analyze whether certain information could be classified as context, Deyetal.[1]providedthefollowingmoregeneralandwidelyaccepteddefinitionthatencompassesthepreviousones:
Contextisanyinformationthatcanbeusedtocharacterizethesitu-ationofentities(i.e.,whetheraperson,placeorobject)thatarecon-sideredrelevanttotheinteractionbetweenauserandanapplication,includingtheuserandtheapplicationthemselves.Contextistypicallythe location, identity and state of people, groups and computationalandphysicalobjects.
Therefore, context involves relevant information on real world entities. Thisinformationneedstobedescribedinastructuredandeasilyextensiblemodeltofacilitatethesharingofcollectedinformation.Therefore,itisimpossibletolimitcontextinformationtoafixedsetofattributesorproperties.
13.2.2 Using RFID to Sense ContextRFID is an emerging technology for embedding sensing capabilities in every-day objects[39] and is gaining momentum as a popular means for automatic
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identification and tracking in supply chain management. Each tag contains auniqueIDnumberthatcanbereadbyanRFIDreader.ActiveRFIDtagshavetheirownpowersupplytotransmittheirsignal,whilepassiveonesusetheelectricalcurrentinducedintheantennaduringreceptionoftheincomingradiofrequencysignalemittedbytheRFIDreader.Thepresenceofaninternalpowersupplyhelpstoextendtherangeofoperationandtheamountofinformationthatcanbetrans-mitted.Themajorityofpassivetagstypicallyhaveanywherefrom64or96bits(torepresentanelectronicproductcode(EPC)[13]asshowninFigure13.1)to1kbofnonvolatileEEPROMmemory,whileactivetagshavebattery-backedmemoriesashighas128kbandmore.
Theabilitytostoreandremotelyrecognizetagsatahighpace(intheorderofhundredspersecond)makesRFIDapromisingtechnologyforidentificationandlocatingpurposesincontext-awareandpervasivecomputing[36].RFIDtagsaremainlyusedforassettrackingandininventorysystemsatlibrariesandshoppingmallswheretheyreplacetheolderbarcodetechnology.However,RFIDtechnologyisalsobeingappliedtothetaggingofhumanstoidentifythemaswellaslocatetheirwhereabouts.RFIDenabledE-passportsareissuedbymanycountries,whileimplantableRFIDchipsareusedtotrackpatients inahospitalandaccesstheirmedicalrecords.Philiposeetal.[28]andSmithetal.[35]alsoillustratehowRFIDtechnologycanbeusedtoinferhumanactivity.Assuch,itisclearthatRFIDpro-videsaddedvaluetothedomainofcontext-awarecomputingandtotheInternetofThingsparadigmingeneralforsensingidentityandlocation.
13.2.3 Requirements for Representing and Exchanging Context
Forhumans,itisnaturaltocommunicateandinterpretcontext.Thegoalofusingopencontextspecificationlanguagesistosimplifythecapturing,transmission,andinterchangeabilityofthiscontextbetweensystems.Differentmodelingapproachesforcontexthavebeeninvestigatedinthepast.Amodelconsistingofkey-valuepairsisthemostsimpleapproachtorepresentcontext,butlackstheabilitytostructureinformationandonlysupportsexactmatching.Markupschememodelstypically
96–BIT ELECTRONIC PRODUCT CODE (EPC)
Header
8 bits01
28 bits0000A89
24 bits00016F
36 bits000169DCO
EPC Manager Object Class Serial Number
Figure 13.1 A passive RFID tag having 96 bits of memory to represent an EPC number.
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introduceafixedstructureandallowtoexpressmorecomplexrelations,suchasassociations. These types of models are frequently used to capture user profiles(e.g.,FriendofaFriend(FOAF)[5])anddeviceprofiles(e.g.,CompositeCapabli-ties/Preferences Profile (CC/PP)[24] and User Agent Profile (UAProf)[16]). Sofar,ontologies,providingaspecificationofaconceptualization[17],seemtobethemostpromisingway togowhenmodelingcontext[37,7,18,38].Ontologiesarewellknownintheknowledgerepresentationcommunitytomodelconceptsandtherelationshipsthatholdamongthemandtheirsemanticinterpretationisuniversallyaccepted.Figure13.2illustratesagraphicalrepresentationofthe
Activity Role
Profile
Mood
User
HardwareSoftware
Platform
Environment
Resource
I/O
Environmental ConditionTimeLocation
has Time
has Location
has Environment
requires Platformprovides Software
provides Serviceuses Service
provides Hardware
is a
uses IO Devicehas Task
has Activity has Role has Mood
has Profile
has Profile has Profile
association
has Environmental Condition
Class
Service
Task
ONTOLOGY–BASED MODELING OF CONTEXT–AWARENESS
Figure 13.2 The CoDAMoS context ontology that models the user, platform, service, and environment concepts and interrelationships with other relevant classes.
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Context-DrivenAdaptationofMobileServices(CoDAMoS)contextontology[30].ManydedicatedandXML-basedlanguagesexisttomodelontologies,butthebestknownlanguageistheWebOntologyLanguage(OWL)[20],amarkuplanguageforpublishingandsharingdatausingontologiesontheWorldWideWeb.FollowingisareviewofsomeofthemainrequirementsforanopencontextspecificationtobeusedforexchangebetweencomputationalartifactsintheInternetofThings:
Comprehensivedomaincoverageandterminology:Anopencontextspec-ificationlanguageshouldmakeavailableaterminologythatprovidesappro-priatecoverageandacomprehensiverepresentationofadomaininordertomodelmostof the concepts and termsneeded fordescribing entities in aparticular domain. Concepts may be modeled with multiple synonymousrepresentationsandmayhavehierarchicalrelationshipstootherconcepts.Semantic nonambiguity and expressiveness: Information semanticsinvolvetheuniforminterpretationofaconcept.Thisrequiresastrictsup-port fornonambiguity in the specification language to ensure that eachconceptintheterminologyhasonlyonemeaning.Semanticexpressivenessistheabilitytoeasilyenhancetheknowledgedomainusingthesemanticprimitivesofthespecificationlanguage.Moreadvancedsemanticspecifi-cationlanguagesforcontextprovidesupporttomodelspecializationandinheritancerelationships,aggregation,dependenciesandconstraints,etc.Processingcomplexity:Somelanguagesrequirequitecomplexprocessingstepsforboththedataacquisitionandprocessing(e.g.,reasoningandinfer-ence)parts.Forexample,contextmodelsusingResourceDescriptionFrame-work(RDF)[4]orOWL[20]mayrefertootherremotelyavailablecontextmodels todetail thesemanticsandrelationshipsofconceptsbeingreused.This,ofcourse,isagoodthingasitimprovesknowledgesharing,interoper-ability,anduniversalinterpretation.However,italsoincreasesthecomplexitytoprocesscontextmodels.AstheInternetofThingstargetscomputationalartifactsofdifferentshapesandsizes,anappropriatebalanceshouldbefoundbetweenprocessingcomplexityandlanguageexpressiveness.Specification language interoperability:There isnoone single specifi-cationthatwillsolveallissueswithrespecttocontextprovisioninginanopenfashion.Forsomepurposes,theuseofaparticulardomain-specificlanguagemayalreadybe sopervasive that this in itselfwouldbeoneofthereasonsnottoreimplementthesameconceptsinanothermoregenericspecificationlanguage.Therefore,theeaseofreusingandintegratingdiffer-entdedicatedspecificationlanguagesisalsoanimportantconcern.
Forinformationtobeprocessedautomatically,itgoeswithoutsayingthatthemarkupneedstoconformtoastandardformatthatisacceptedbyasmanypartiesaspossible.Openstandardsareahottopicatpresentforexchangingdocumentsinaformatthatcanbereadandmodifiedbydifferentparties.AlotofattentionispaidtoXMLformatsastheHolyGrailforinterchangeability.However,forcontext
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specificationandexchange,itisnotonlyimportanttobeabletoprocessthecon-textinformation,butalsotointerprettheinformation.AlargedifferencewiththeXML-baseddocumentationformats,suchasOpenDocumentFormat(ODF)[26]andOpenXML[12],isthatthesemanticsofcontextinformationshouldbesharedbyallthepartiesinvolved,preferablywithinthecontextmodelitself.Tothisextend,XMLonlyprovidesatree-basedstructuretospecifyinformation.Theinterpreta-tionistotallylefttotheuserortheprogram.
Manyopenspecificationlanguagesaregeneralpurposedescriptionlanguages(e.g.RDF[4] and OWL[20]), while others target a very specific domain. Forexample, dedicated languages and specification formalisms have been proposedto model the hardware and software characteristics of mobile handheld devices(e.g., CC/PP[24] and UAProf[16]). Regarding RFID technology, it was onlyrecently(2007)that theElectronicProductCodeInformationServices (EPCIS)standard[14] was ratified, effectively providing an XML schema binding and abindingtoSimpleObjectAccessProtocal(SOAP)overHTTPviaaWSDL(WebServiceDescriptionLanguage)totheEPCinformationonanRFIDtag.Someofthesedomainspecificformats,suchasUAProf,builduponageneralpurposelan-guagelikeRDF,asillustratedinFigure13.3.Notonlydoestheexpressivenessof
NOKIA N95–1 USER AGENT PROFILE
<rdf:RDF xmlns:rdf=“http://www.w3.org/1999/02/22–rdf–syntax–ns#” ... <rdf:Description rdf:ID=“Profile”> <prf:component> <rdf:Description rdf:ID=“HardwarePlatform”> <prf:Vendor>Nokia</prf:Vendor> <prf:Model>N95–1</prf:Model> <prf:BitsPerPixel>18</prf:BitsPerPixel> <prf:ColorCapable>Yes</prf:ColorCapable> <prf:CPU>ARM</prf:CPU> <prf:ImageCapable>Yes</prf:ImageCapble> <prf:Keyboard>PhoneKeyPad</prf.Keyboard> <prf:NumberOfSoftKeys>2</prf:NumberOfSoftKeys> <prf:ScreenSize>240×320</prf:ScreenSize> <prf:ScreenSizeChar>15×6</prf:ScreenSizeChar> <prf:SoundOutputCapable>Yes</prf:SoundOutputCapable> <prf:TextInputCapable>Yes</prf:TextInputCapable> <prf:VoiceInputCapable>Yes</prf:VoiceInputCapable> </rdf:Description> </prf:component>
</rdf:RDF
Figure 13.3 An partial description of a wireless device using the RDF-based User Agent Profile specification.
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theselanguagesdiffer,theyalsodistinguishthemselvesinmanagingorprocessingcomplexity.Assuch,thereisnosingleone-fits-allcontextspecificationlanguage.
13.3 Trends in Context-Aware Computing within Service Orientation
Thougheffortsincontextawarenessresearchonlyseemtoreachthepublicataslowpace,wenoticethattheneedforknowledgeengineeringmethodologiesbecomesagrowingconcerninthedesignofsoftwarearchitectureswhenbuildinguser-awareservices.TheseevolutionsbecomeapparentinboththeSOAworldofITservices,aswellasfortheSDPsofthetelecommunicationsdomain.AnysoftwarearchitecturefortheInternetofThingswillfacethesameconcerns,butatamuchlargerscaleasthenumberofinformation-sharingentitieswill,intheend,outnumberhumancommunication.
13.3.1 Context-Enabled Service Oriented Architecture and the Semantic Web
ServiceOrientedArchitecture(SOA)representsthecurrentstate-of-the-artinsoft-warearchitecturefortherapiddeploymentofnewservices.Itenablesthecreationofnewservicesorapplicationsbyconnectingtogetherexistingservicesandpro-posesfunctionstomanagetheservicelifecycle.ThemainmotivationbehindSOAforacompanyistocreateabusiness-alignedarchitecturetobetterreacttochang-ingcustomers’needs.Ifthemarketchanges,newservicescanbecreatedbyreusingexistingservicesandbydevelopingnewserviceswhereneeded.ASOAalsoenablesacompanytoleveragepreviousinfrastructureinvestments,byexposinglegacyser-vicesas traditional services in thearchitecture:ASOAincreasescode reuseandmodularity.
A service-oriented architecture targeting thegrowingproliferationofRFID-equippeddeviceswithintheInternetofThings,whereeachcomputationalartifactmayaccessmultipleserviceswithindiversecontexts,willbecomeadauntingtaskwithoutproperidentitymanagement.Theuseofcontextawarenesshelpstopro-videmorefine-grainedaccesscontroltoinformationandservices.OneillustrationofthistrendispresentedintheworkofArdagnaetal.[3]whereposition,move-ment,andinteractionpredicatesareintroducedinauthorizationpoliciesrelyingonGroupeSpécialMobile(GSM)/third-generation(3G)technologiestoachieveloca-tion-constrainedaccess.WiththeintroductionoftheE-passport,fittinginRFIDinformationintopolicyenforcementrulesis justasmallstep.FormanagingtheinformationflowintheInternetofThings,contextawarenessisbecomingamuchlargerconcerninSOAthanitisatthemoment.
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Another emerging trend is coming from the Semantic Web community.AlthoughtheWSDL[8]hasbeenverysuccessfulasasyntacticspecificationlan-guagetointeractwithWebservicesusingdifferentbackendenvironments,itdoesnotprovideanysupportforaconsistentinterpretationoftheWebservicecontent.Theuseofontologieshasalreadygainedmuchattentionforthesemanticmodelingofcontext,asillustratedinFigure13.4.Theapplicationofontologiesisalsofind-ingitswayinnewWebservicespecifications,includingOWL-S[25],METEOR-S[34],WSDL-S[2],WSMO[9,15],andothers,toaugmentservicedescriptionsinordertoautomatetheirdiscovery,composition,andinvocationinpervasivecom-puting environments. The services, that were previously only described by theirpublicinvocationinterfaces,arenowenrichedwithmachine-interpretableseman-ticsby referring toand reasoningonestablishedontologies that encapsulate themeaningoftheservice.Also,fortheInternetofThings,theuseofontologieswithinthearchitecturemayhelptomakesenseofitall,forboththecontextinformationaswellastheservicesbeingoffered.
13.3.2 Context-Enabled Service Delivery PlatformsDuringthelastdecade,thetelecommunicationsworldhastransformedradicallyduetotheshifttowardInternet-styleinfrastructuresforthedeliveryofmultimedia-enabledcommunicationservices.Today’sverypopular,IP-basedVoIP(VoiceoverInternetProtocol)systemsaretheresultoftheevolutionfrommonolithicandiso-latedinfrastructurestoservicedeliveryplatformsthatadopttheIPnetworkastheir
CONTEXT–AWARENESS AND THE SEMANTIC WEB “LAYER CAKE”
Context–awareapplications for theInternet of Things
Context Content
Trust
Proof
Logic
Ontology vocabulary
RDF + rdfschema
XML + NS + xmlschema
Unicode URI
Reasoning
Interference
Equivalence
Location TimeSUMO WSMO
CC/PP FOAF
PIDF RPIDEPC
Syntax
Data
Semantic Markup
Dig
ital S
igna
ture
Figure 13.4 Aligning context awareness and standardized specifications for the Internet of Things along the Semantic Web “layer cake” (Courtesy of T. Berners-Lee).
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communicationnetworkandbasetheiroperationsonopenstandardsandproto-cols.Theseservicedeliveryplatformsenablearichercommunicationexperiencebyprovidingservicesthatgobeyondleavingavoicemessagewhenyourfrienddoesnotanswerhiscellphone.Withconventionalcommunication,youhavenoideawhenyourfriendwillgetyourmessage,perhapsleavingyounochoicebuttocallbackseveraltimes.Ifyouonlyknewwhereyourfriendwasatthatmoment… .
PresenceandavailabilityarejusttwoofthemainfeaturesthattheseSDPsoffer,togetherwiththeadoptionofanotherpopularInternetapplication:InstantMessaging.Apresenceserviceenablesaselectivegroupofusers,the“buddylist,”tobenotifiedofyouravailabilityandyourpreferredwayofcommunication(mail,telephone,instantmessaging,etc.).This informationispassedonusingtheSessionInitiationProtocol(SIP).SimilartoHTTPandSOAPforWebservices,theSIP[19]isthemostimpor-tantprotocolforInternettelephony,supportinguser,session,andservicemobility,andamajorbuildingblockformultimediaandvoiceservicesonIPMultimediaSystems(IMS).SIPisundercontinuousexpansiontosupportnewtypesofcommunicationandinformationthatwerebeyonditsscopewhenitwasinitiallydefined.Manyoftheseadd-onSIPstandardsareusedtosketchthecontextoftheusersandtheirappliances,ortonotifyremotesubscribersofachangeinthiscontext:
SIP Specific Event Notification: This is an extension that allows SIPnodestorequestinformationfromremotenodes.Beingagenericpackage,itcanbeusedtonotifyandconveyanycontextualchangetowhomitmayconcernwhensuchaneventhasoccurred.PresenceInformationDataFormat(PIDF):ThisisanXMLdocumentthat provides presence information about a presentity, including statusinformation and optionally contact addresses, timestamps, and textualnotes.AnexampleisgiveninFigure13.5.
n
n
PRESENCE INFORMATION DATA FORMAT
<?xml version=“1.0” encoding=“UTF–8”?><presence xmlns=“urn:ietf:params:xml:nspidf” entity=“pres:[email protected]”> <tuple id=“123456”> <status> <basic>open</basic> </status> <contact priority=“0.75”>tel:+32987654321</contact> <timestamp>2007–03–15T17:26:21Z</timestamp> <note>I am busy right now ...</note> </tuple></presence>
Figure 13.5 Specifying presence within SIP using the basic PIDF format.
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Rich Presence Information Data Format (RPID): This format buildsuponPIDFandaddselementsthatprovideadditionalinformationaboutthepresentity�(location,mood,activity,etc.)anditscontacts.OtherrelatedSIPstandards:CommonProfileforPreference,CommonProfileforInstantMessaging,ContactInformationinPresenceInforma-tionDataFormat,TimedPresenceExtensionstothePIDF,etc.
Wecanobservethat,giventhelistofSIPspecificationsanddraftrecommenda-tions,presence isan importantconcern in telecommunications. In supplychainmanagement, where RFID technology typically has a strong foothold, presenceandavailabilityplayanimportantroleaswell.Althoughproductswillnotdirectlycommunicatetheirpresencetoallinterestedpartiesbythemselves,itisclearthattheflexibilityoftheSIPsignalingprotocolmakesitanexcellentcandidatetodeliverreal-timeandup-to-datecontextinformationtoallsubscribers.
13.4 Service Provision in a Context-Aware, Converged Service Architecture
Interoperability between Web service-and telecommunication-oriented architec-turesisacomplexissue.AserviceinSOAisessentiallytransaction-basedandreliesonanarchitecturethatoftenbuildsuponthefunctionalityofanenterpriseservicebus(ESB)toprovidemessagebrokering,routing,datatranslation,andtransforma-tion.AservicewithinaSDPneedstodealwithamultitudeofpoint-to-pointcon-nectionsandshort-livedeventsthatmustbegenerated,propagated,andprocessedwithalowlatencytoguaranteeaminimalqualityofservicelevel.TheproposedarchitecturefortheInternetofThings,therefore,integratesbothkindsofservicesatthesessionlevelbecausethatiswheretheinteractionbetweentwoservicesstartsandwhereitcanbenefitthemostfromcontextinformation.AsWebservicesandtelecommunicationservicesusesimilarthoughcompetingstandardsforinforma-tionexchange;anenterpriseservicebusisusedinsidethearchitecturetomanagethemessageconversionandroutingduringasession.Ahigh-levelconceptualover-viewofthearchitectureisgiveninFigure13.6.
The goal of introducing context awareness in a converged service-orientedarchitectureistosimplifythediscoveryofinformationaboutanentitywhenthisinformationcannotbeeasilysearched,isnotmadeexplicitintherequiredformat,orneedsaggregationwithother information sourcesbefore it canbeused.Ourcontextmanagementsystem[29]representsitselfasanenablingserviceinthecon-vergedservice-orientedarchitecture,inasimilarwayasbillingandpolicyenforce-mentdo.Neitheroftheseservicesprovideanyfunctionalitydirectlytotheclient,butdo so toother enabling and end-user services. Similar tobilling andpolicy
�Presentity: A presentity(presenceentity)providespresenceinformationtoapresenceservice(RFC2778).
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enforcement,specialcareistakentomakesurethatcontextinformationbelongingtodifferententitiesisprocessedandstoredseparately.Fromanarchitecturalpointofview,however,ourcontext-awarenessenablingserviceactsasanyotherservicewhoselifecycleinthesystemneedstobemanaged.
13.4.1 Context Management as an Enabling ServiceContextmanagement from an enabling service perspective involves the followingfunctionalrequirements,nomatterwhetherthecontextinformationisusedlocallyorneedstobedeliveredtoaremotecomputationalartifactsomewhereonthenetwork.
ContextAcquisition:ThisfunctiongathersinformationfromRFIDtags,sensors,userprofiles,presenceservers,orotherinformationprovidersinthesystemitselforonthenetwork.Ingeneral,itmonitorsforcontextthatischangingandcollectsallinformationthatremoteentitiespushtothesystemusingSOAP,SIP,oranotherdomain-specificcommunicationprotocol.ContextStorage:A context repository ensurespersistenceof context infor-mation.It savesrelevant information inawaythatqueriesand informationupdatescanbehandledefficientlywithout losingthesemanticsofthedata.It,therefore,preservestheinformationitself,e.g.,‘Age=23;’towhichentityitbelongs,e.g.,apersonoradevice;whenandbywhomitwasacquired;and
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CONTENTMANAGEMENT
CONSUMER SERVICES
ENABLING SERVICES
SERVICE EXECUTION AND CONTROL
WEB SERVICES TELECOM SERVICES
WSDL, SOAP, BPEL SIP, PIDF, RPID
ORCHESTRATIONDISCOVERY
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Figure 13.6 Context as an enabling service in a converged service-oriented architecture.
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howtheinformationrelatestootherinstantiatedcontextconceptsbyreferringtotherightontologyinthesemanticknowledgebase,alsostoredinthecontextrepository.ContextManipulation:Thispartaggregatesandreasonsoncontextinfor-mationtoprovideinformationinasuitableformatwhenneeded.Besidesareasoningenginethatexploitssemanticrelationshipswithinontologies,theenablingservicealsoprovidesadaptersthattransformcontextinformationtochangethewayinformationisrepresented.Forexample,atemperatureexpressedin°Ccanbetranslatedinto°Fusingstraightforwardconversionrules.Classificationsacrificesaccuracyoflow-levelinformationforthesakeofobtainingmoremeaningful information.Forexample,ageographicallocationoflongitudeandlatitudecoordinatescanbeconvertedintoacityrepresentation.Asmanyapplicationdomainsproposesimilarthoughcom-petingstandards,partofthemanipulationisalsotobridgethestandardsinteroperabilitygapwherepossible.
Ahigh-leveloverviewofthebuildingblocksofthecontext-awarenessenablingserviceisgivenFigure13.7.
13.4.2 Conveying Context and Distributed StorageAfter having consolidated context information from various acquisition systems(sensors,people,devices,etc.)andremoteinputchannels(services,databases,etc.),the collected informationmaybe selected fordistribution to remote subscribers(people, services, devices). When information is gathered from or needs to be
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USER PROFILE
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ONLINE MUSICSTORE
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Figure 13.7 Building blocks of the context awareness-enabling service.
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delivered to a remote entity, choicesneed tobemadeonwhere contextwill bestored.Theobviouschoicewouldbeclosetotheareawhereitisconsideredrelevant,andperhapsbeduplicated ifnecessary. Ifcontext is stored locallyonthedevicethatsensedtheinformation,itisreadilyavailableandroundtripsonthenetworktoretrievetheinformationareavoided.However,iftheinformationisalsousefulforotherparties,thenitmakessensetostoretheinformationremotelyonareposi-torythatismoreeasilyaccessible.Thefollowingconcernsaretakenintoaccountwhetherinformationshouldbestoredlocallyorremotely:
Scopeofrelevance:Certaininformationcanberelevantonlyforcompu-tationalartifactsthatinteractinparticularwithlocalservices.Anobviousexample is the intelligenthomeenvironmentwherethe informationthatphotovoltaiclightsensorsinthehouseprovide,isnotofinterestoutsidethehomeenvironment.Informationsensitivity:TrackinginformationretrievedfromRFIDtagscouldbeofinteresttomultiplepartiesonthenetworkandbemadeavail-ableonaremoteserverforfurtheranalysis.Personalinformation,ontheotherhand, is keptprivate onpurpose andonly sharedwith authorizedentities.Althoughprivacyissuesareanimportantconcernincontext-awarecomputing,wewillnotgointodetailhereasprivacyisalreadycoveredtoalargeextentinotherchaptersandinthespecializedliterature.Information currentness and period of relevance: Static and profiledinformationislikelytoremainvalidforlongerperiods.Forexample,thepositionoffixedbeaconsisinformationthatishighlysuitedfordistribu-tion,assynchronizationdoesnotneedtooccuroften.Volatileinformationontheotherhand,suchasthecurrentsystemload,maynolongerbeaccu-rateorrelevantwhenitisfinallyremotelystoredinarepository.Cachingforinformationreachability:Ifsomesensorinformationcanbeobtainedquiteeasily,thenstoringtheinformationmaynotbeworthwhile.However,assomeappliancesmighthavenodirectconnectiontocontextsensorsthatprovideusefulinformation,arepositorywithstandardSOAPor SIP interfaces can collect and make the information accessible to allinterestedparties.Exploitinginformationhistory:Insomecases,anappliancemightwanttoexploitthehistoricvaluesofacertaincontextattributeinordertoderivenewinformation.Forexample,bytrackingthecurrentposition,thetraveleddistancecanbederivedandusedtoreimbursetravelingexpenses.Althoughtheinformationisnolongeraccurate,itisstillconsidereduseful.
Itisclearthatthesoftwarearchitectureitselfcannotalwaysdecideifcontextinfor-mationshouldbedistributedornot.Thereasonforthisisthatcontextisallaboutrelevantandusefulinformationandthesoftwarearchitecturemustbeinformedbyitsclientsaboutwhatinformationtheyconsiderrelevantfortheirpurposes.
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13.5 Context Awareness from RFID to the End-User in the Internet of Things
The digital lifestyle chapter of the digital.life ITU Internet Report 2006[23]describesseveralfuturisticscenariostowardcontext-awareservices.Wewillbrieflysummarizethemandthendiscusshowourconvergedservice-orientedarchitecturewouldaccomplish the tasks in these scenarios if thearchitecturewouldbe fullyimplementedanddeployedonalargescale.
1. Youarewalkingaroundinthecityandyourfavoriteshopcallsyouonyourmobilephone.Ithasdetectedthatyouareintheneighborhoodandwantstopromotesomegoodsyoumightbeinterestedin.
2. Youfindtheshirtofyourdreams,butitisnotavailableanymoreinyoursize.YouscantheRFIDtagtolookforbranchesthathavetheshirtinstockandrequestdrivingdirectionstothenearestbranch.
3. Afteryourshoppingexpedition,youheadbacktoyourcarandwhilegoinghomeyourunlowonfuel.TheGPSnavigationsysteminyourcarinformsyouaboutnearbygasstations.
4. Thenextmorning,yourumbrellanotifiesyouasyouleaveforwork,thattheweatherforecastappearstopredictrainforthisevening.So,youbetterbepreparedandtakealongthatumbrella.
5. Atwork,yourtelephonehandsetdetectsahighbodytemperature.Itseemsyouareabitfeverish.Thedisplayshowsawarning,alongwithhealthcareinformationandcontactinformationofanearbydoctor.
Mostoftheabovescenariosrelyonlocationawarenessoftheuser.ThislocationcouldbeobtainedusingRFIDorBluetoothtechnologyinstalledinthecellphoneof theclient,or fromaGPSnavigationsysteminthecar.Thetypesof locationinformationisdifferent(identifier,MACaddress,latitude,andlongitude)andwilllikelyneedtobeconvertedfirstbythecontext-awareness-enablingservicebeforeitcanbeusedbyoneoftheend-userservices.Presenceawarenesscomesintoplayinscenario1and5.Thecontext-awareness-enablingserviceverifiesfirstusingtheSIPprotocolifthepersoninquestionisavailableandwhatkindofcommunicationhecurrentlyprefers,andthensendsamessagetothecorrespondingaddress.Userprofilesareusedbytheshopownertolinkanidentitywithpreviouslypurchasedgoods,andatclientsidetostorethehomeandworkaddress,thesizeofyourshirt,SIP contact information, etc. Some context information conversion is needed toconvertthecurrentlocationtoafour-letterMETARweatherstationidentifiertogetthelocalweatherreportathomeandatwork.Sensortechnologyisusedtochecktheamountof fuel, tocheck thebody temperature, todetectmovementsat thefrontdoorofthehouse,etc.ThesecondscenariocouldbeanorchestrationofWebservicesthataresemanticallydescribedusingOWL-S.AfterusingSOAPtosend
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theEPCoftheshirtandthesizeyouneedtotheWebservice,youobtainalistofaddresses.Foreachoftheseaddresses,anotheronlinerouteplanningserviceisusedtocomputethedistancetothenearestbranch.
TheabovescenariosprovideamixtureofWebserviceandtelecommunicationserviceorchestrations,contextawareness,RFIDandsensortechnology,localandremoteservices,SIPandSOAPcommunication,andsoon.Althoughareal-lifedeployment of the architecture has not been done to test the feasibility, we areconfidentthatourcurrentarchitecturecanaccomplisheachofthesetasks.Alltherequirementshavebeencoveredintheprevioussectionsandinteroperabilitysup-portisbuiltintothearchitecturetomakethesescenarioswork.
13.6 ConclusionsTheInternetofThingsisallaboutconvergenceandintegrationofthelatestadvance-mentsintheresearchareasofsoftwareandhardwarewithindustrialtechnologiesinventedmanydecadesago.Indeed,althoughRFIDisoneofthecornerstonesofthisnewcomputerparadigmandbecomingmorewidespreadnowadaysduetoitslowproductioncosts,itsinventionstemsfromtheWorldWarIIperiodwhenitwasdevelopedformilitarypurposes.Inthischapter,wehavehighlightedtwoconcernsofgreatimportancefortheInternetofThings.Onecomesfromthesoftwareengi-neeringdomain,namelytheuseofagoodsoftwarearchitecturestyleforthedesignofanysoftwaresystem,andanotheroneisrelatedtotheknowledgeengineeringdomain and deals with context awareness, also one of the goals of the InternetofThings.Researchcarriedoutinthecontext-awarecomputingdomainaimstocreateapleasantuserexperienceattheworkplace,inpublicareasaswellasinthehomeenvironmentbysimplifyinghumaninteractionswitheverydayservicesandmakingthemlessintrusive.WehavediscussedhowRFIDtechnologycancontrib-utetocontextawarenessasawaytoidentifyandlocateeverydayobjectsaswellashumans,forthatmatter.
Wehave arguedwhy serviceorientation is a good architectural style for theInternetofThingsbecauseit leveragesexistingapplicationsbyexposingthemastraditional services in thearchitecture. It increases reuseandmodularity, speed-ingup the integrationeffort.Wehaveproposeda servicearchitecture thataimstobridgecontextawarenesswiththeworldsofWebservicesandtelecommunica-tionservices.Bothapplicationdomainshavecontributedintheirownwaytothedevelopment of context-aware services by standardizingdescription formats andprotocolstoconveyrelevantinformationtowhomitmayconcern.Standardizationisgood,onlyifnotforthefactthatmanyofthemaresimilarandcompetingwithoneanother.Forthisreason,wehaveintroducedcontextawarenessasanenablingservice in the architecture, leveraging information from both areas at a centralplace. The context-awareness-enabling services is responsible for the acquisition,
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persistency,andmanipulationofinformationtomakesurethattherightinforma-tioncanbedeliveredattherightplaceattherighttime.
13.7 Open IssuesDespitethegreatpotentialofcontextawarenessfortheInternetofThings,therearestillsomehurdlestocrossthatmayslowdowntheadoptionofRFIDandotheremergingtechnologies.Oneoftherepercussionsofcontext-awarecomputingistheinvasionofone’sprivacy.Whiletheaimistoincreaseconveniencebyreducingtheamountofinteractionsbetweenusersanddevices,itisofutmostimportancetonotlosesightofprovidingalevelofusercontrolinordertosetthemindsatease.OnlywhenpeoplearepartoftheInternetofThingsandfeelincontrolwillthisnewwayofcomputinghaveachanceofbeingwidelyadopted.
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