[IEEE 2007 2nd International Conference on Pervasive Computing and Applications - Birmingham, UK (2007.07.26-2007.07.27)] 2007 2nd International Conference on Pervasive Computing and Applications - Research on the Architecture of Ontology-based Context-aware Application in Pervasive Environment

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<ul><li><p>Research on the Architecture of Ontology-based Context-aware Application inPervasive Environment</p><p>Yongquan Dong"12, Qingzhong Lil,Yuliang ShilI School ofComputer Science and Technology, Shandong University, Jinan, P.R. China</p><p>2 School ofComputer Science and Technology, Xuzhou Normal University, Xuzhou, P.R. Chinadongyongquan@,mail. sdu. edu. cn lqz@,sdu. edu. cn liangyus@,sdu. edu. cn</p><p>Abstract</p><p>With the prevalence ofpervasive devices, plentyof applications need to support context awareness.Due to the heterogeneity of context information, it isnecessary to provide a set of common vocabularieswith shared semantics. Based on above requirements,the paper presents an architecture ofontology-basedcontext-aware application in pervasive environment.In the architecture context processing is regarded asa separated module which conforms to the principleof software engineering, "seperation of concernsThe architecture enables applications to focus on theinformation that they desire, and reduces the need toworry about how contextual information is retrieved.In order to reuse of the ontology, the paper designstwo level's ontology-generic ontology and domain-specific ontology which unifies semantics of contextinformation. At last an example scenario of homedomain is given to illustrate the rationality andeffectiveness ofthe architecture.</p><p>Keywords: Pervasive Computing, Ontology, Context,Context-aware Application.</p><p>1. Introduction</p><p>Pervasive computing paradigm is firstly proposed byWeiser[1-2], which will become "third wave ofcomputing". With the prevalence of pervasive devices,users can hold many electronic devices to facilitate theirdaily lives and work. They have to deal with diversedevices (mobile or fixed) with diverse interfaces andused in diverse environments. It is imperative to enabledevices and applications to automatically adapt tochanges in their surrounding physical and electronicenvironments. Context [3-4] is any information thatcharacterizes a situation related to the interactionbetween users, applications, and the surroundingenvironment. The usage of context requires manyapplications to support its processing. So it is necessaryto design a reasonable architecture to make currentapplications support the processing of context withoutmodifying themselves. From the perspective of</p><p>software engineering, the architecture should conformto the principle of "separation of concerns", that is,application designers need not to care about the detailsof how to derive the context that applications canunderstand.</p><p>Another problem is the different representation ofcontext. The lack of common context specificationraises some issue of interoperability, reuse. Ontologyprovides a formal, explicit specification of a sharedconceptualization of a domain. Using ontology toprovide the semantics of context information is apromising area.</p><p>Based on two above problems, the paper proposes anarchitecture of ontology-based context-awareapplication in pervasive computing. The examplescenario suggests that the architecture is reasonable andapplicable.The remainder of the paper is structured as follows.</p><p>Section 2 presents a context layer model. Section 3focuses the architecture of ontology-based context-aware application and introduces the details of each part.Section 4 elaborates on the context ontology, whilesection 5 presents an example scenario to suggest thatthe architecture is reasonable and effective. Finally, insection 6 conclusions are drawn, while an outline offuture plans is provided.</p><p>2. Context Layer Model</p><p>The generation of context is not one time, but manytimes in which the abstraction of context will begradually enhanced. We divide context information intofour layers. As is shown in Figure 1, the four layerscontain physical context, interpreted context, integratedcontext and applicable context from low level to highlevel. The physical contexts describe contexts which arederived from the environment. The interpreted contextsrepresent contexts which are be transformed and bemapped to contexts that are defined by applying anaccepted vocabulary for simplification. The integratedcontexts describe contexts which relate to an entity in asituation. The applicable contexts are built from highlyspecific contexts whose contents are adapted to theapplication.</p><p>1-4244-0971-3/07/$25.00 )2007 IEEE.</p></li><li><p>Applicable Context</p><p>ntegrated Context</p><p>nterpreted Context</p><p>Physical Context</p><p>Figure 1 Context Layer Model</p><p>3. The Architecture of Ontology-basedContext-aware Application</p><p>In this section, we present an architecture ofontology-based context-aware application in pervasiveenvironment and introduce the details of each part. Thearchitecture generalizes the foundations laid in[3-5] toprovide a higher abstraction.</p><p>The architecture of ontology-based context-awareapplication is shown in Figure 2.</p><p>Context-ware Application Layer</p><p>Context Mildlleware Layer Cohtext I_feienne Engie</p><p>OntoloEoe La text Integrator</p><p>Mr gw~~~~~ohtext Interpreter = | e</p><p>Context</p><p>Ontology Context Collector |Finder</p><p>|EryironrLenLt Resource LaErer ( SenLsors, S ervic es, Devices ..</p><p>Figure 2 The Architecture of Ontology-basedContext-aware Application</p><p>The architecture is divided into three layers that areenvironment resource layer, context middleware layer,and context-aware application layer from bottom to top.The function of each part is described as following.</p><p>(1) Environment Resource Layer. It contains manyresources such as sensors, services and devices whichare the sources of the production of context. Theseresources constitute a pervasive environment.</p><p>(2) Context Middleware Layer. It focuses on theprocessing of context, which contains contextacquisition, context interpretation, context integrationand context inference etc. In order to support contextsharing, this layer incorporates ontology to unify thecontext semantics meaning. As a separated layer, it willadapt well to any existing application withoutsupporting context.</p><p>The layer has many modules each of which achievesspecific functions. In Figure 2, we omit the word"module" in each module.</p><p>Context collector module is responsible foracquiring the raw data from the resources inenvironment resource layer. Context interpreter moduleanswers for producing the interpreted contexts andraises the level of abstraction of context information.Context integrator module gathers context informationrelated to an entity, that is, integrated context. If thereare many context collectors which generate samecontext, the context integrator decides which contextcollector to use according to the sensor's accuracy anderror rate. Context inference engine module infersadditional and not directly observable contextinformation which conforms to applicable context anddetermines which application to run according to rulesin knowledge base which is easy to be managed by user.Context storage module receives the physical context,interpreted context, integrated context and applicablecontext in order to maintain a history of all contextswhich can be used to establish trends and predict futurecontext values. Context ontology module provides aunified, well structured scheme for the semanticrepresentation of context information which all thecontext must conform to. Context ontology managermodule dynamically updates context ontology and usesit to interact with peers in pervasive environment.Finder module answers for maintaining a registry ofwhat capabilities existing in the architecture andmanaging the communications between each contextmodule and the application.</p><p>Each module has the same interface that willfacilitate easy usage. The interface is as shown inFigure 3. Every module has the notification, callbackand polling interface and its core functions. Notificationinterface is responsible for notifying the interestedapplications when context has changed and conformedto the conditions that the relevant applications havepreset. Callback interface allows applications to obtainall level of context. Polling interface takes charge ofallowing applications to be proactive to theenvironment.</p><p>input</p><p>Interface</p><p>NotificatiZonZ |Callback Foiling</p><p>Core Functions</p><p>output</p><p>Figure 3 The Structure of Each Module</p></li><li><p>(3) Context-aware Application Layer. It can utilizethe publish/subscribe mechanism to accept the results ofcontext middleware layer which conform to semanticmeanings of input parameters of applications and canalso use polling mechanism to query all levels ofcontext.</p><p>4. Context Ontology</p><p>A major problem for context is the heterogeneity ofcontext information, and the lack of a general acceptedcontext-specification raises many issues, such asinteroperability, reuse etc. So ontology is incorporatedinto the architecture. The use of ontology to representcontext has already been proposed by others[6-8]. Inthis paper we generalize the use of ontologies accordingto its layered model.</p><p>4.1 Ontology</p><p>In order to support interoperability among pervasiveenvironment, it must be done to share each of domainknowledge. Ontology[9-10] provides a formal, explicitspecification of a shared conceptualization of a domain.It describes concepts in a certain domain andrelationships among these concepts. Because of itsconceptual hierarchical structure and strong expressiveability in semantics, ontology plays an important role inknowledge share and reuse. By using ontology, allresources in pervasive environment can share thedomain knowledge so that they can communicate witheach other seamlessly.</p><p>4.2 Context Ontology</p><p>Context ontology defines a common vocabulary toshare context information in a pervasive computingdomain; and include machine-interpretable definitionsof basic concepts in the domain and relations amongthem.Due to existing a great variety of context, we divide</p><p>the pervasive computing domain into a collection ofsub-domains such as home domain, office domain, etcto reduce the burden of the construction and processingof context ontology. Context ontologies are divided intogeneric ontology and domain-specific ontologies. Thegeneric ontology is generally used context concept inpervasive environment. And the domain-specificontologies are specified context ontology according todomain area. The example of the next section is givento illustrate an example ofhome domain.</p><p>ig 4 a rch diagrAm if oGentlii i Prson Re5{Us 1.&lt; i0 12;,rifVO)nto(logynog</p><p>Domallin-Sr)ec i f i C ||0tntto I ogi es E=.</p><p>Figure 4 Class hierarchy diagram for contextontology</p><p>The generic ontology defines the basic concepts ofperson, location, resource and activity as shown inFigure 4. The class Context provides an entry point ofreference for declaring the generic ontology. Person,Location, Resource and Activity are subclasses ofContext. The details of these basic concepts are definedin the domain-specific ontologies which may vary fromone domain to another. Figure 5 suggests therelationships of generic ontology class.</p><p>iEngage In, liaisResoulr.e</p><p>tot eteAPetrsonr iF Locat ion</p><p>Figure 5 The relationship diagram of classes forcontext ontology</p><p>4.3 An Example of Context Ontology</p><p>We adopt the W3C standard OWL to define domainontology. OWL[11-12] is Web Ontology language.OWL is designed for use by applications that need toprocess the content of information instead of justpresenting information to humans. It provides a rich setof constructs with which to create ontologies and tomarkup information so that it is machine readable andunderstandable. OWL builds on RDF and RDF Schemaand adds more vocabularies for describing propertiesand classes and suites well for specifying andexchanging ontologies.The following is an partial OWL representation for</p><p>Figure 4 and Figure 5.</p></li><li><p>mlns:xsd="http://www.w3.org/200 I/XMLSchema#"fxmlns:rdfs="http://www.w3.org/2000/0 1/rdf-schema#"xmlns:rdf="http:llwww.w3.org/1999/02/22-rdf-syntax-ns#"xmlns:owl="http://www.w3.org/2002/07/owl#"&gt;</p><p>... H omit the other generic class except Person</p><p>5. An Example Scenario</p><p>To give the illustration of the architecture, thissection presents a scenario ofhome domain:Tom has entered his house. The temperature sensor in</p><p>the room measures that the temperature is 35 celsiusdegree.The window of the room should be closed andthe air-condition be opened automatically.The window and air-condition both have applications</p><p>to control their status. And the two applications onlyaccept the input parameter of "open/closing". The rulesof determining their status are predefined in theknowledge base. Of course it can be learned fromhistorical data.The two applications are controlled by the people in</p><p>the past. Now in the pervasive environment, they canadapt to the environment change to proactively controltheir status. Figure 6 shows a graph representation ofcontexts based on the example scenario.</p><p>:t} iisVa</p></li><li><p>semantic meaning among applications and the two-levelontology facilitates the reuse of context ontology. Thelast example scenario suggests that the architecture isreasonable and applicable.</p><p>There are many problems to research more in thefuture. The first is the better way to describe the contextinformation with ontology because of the rapid changein pervasive environment. The second is the research onrapid ontology mapping which will make people movefrom place to place to get their tasks done withoutconsidering the semantic heterogeneity of differentplaces.</p><p>References</p><p>[1] W. Mark, "The computer for the 21st century",Scientific American, 1991, 265(3),94- 104.</p><p>[2] M. Dertouzos, "The future of computing",Scientific American, 1999, 282(3),52-63.</p><p>[3] A. K. Dey, "Understanding and Using Context",Personal and Ubiquitous Computing Journal, 2001,5(1),4-7.</p><p>[4] A. K. Dey, G. D. Abowd and D. Salber, "Aconceptual framework and a toolkit for supportingthe rapid prototyping of context-aware applications",Human-Computer Interaction, 2001, 16(2-4),97- 166.</p><p>[5] K. Jeong, D. Choi, S. H. Kim and G. Lee, "Amiddleware architecture determining application</p><p>context using shared ontology", InternationalConference on Computational Science and ItsApplications, Glasgow, United Kingdom, 2006, pp.128-137.</p><p>[6] H. Chen, T. Finin and A. Joshi, "An ontology forcontext-aware pervasive computing environments",Knowledge Engineering Review, 2003, 18(3),197-207.</p><p>[7] A. Ranganathan, R. E. McGrath, R. H. Campbelland M. D. Mickunas, "Use of ontologies in apervasive computing environment", KnowledgeEngineering Review, 2003, 18(3),209-220.</p><p>[8] M. L. Sbodio and W. Thronicke, "Ontology-basedcontext management components for service orientedarchitectures on wearable devices", 2005 3rd IEEEInternational Conference on Industrial Informatics,Perth, Australia, 2005, pp. 129-133.</p><p>[9] S. P. Li, Q. W. Yin, Y. J. Hu, M. Guo and X. J. Fu,"Overview of researches on ontology", JisuanjiYanjiu yu Fazhan/Computer Research andDevelopment, 2004, 41(7),1041-1052.</p><p>[10] W. Zhang and J. Song, "Study on domain ontologyrepresentation, reasoning and integration for thesemantic Web", Jisuanji Yanjiu yu Fazhan/ComputerResearch and Development, 2006, 43(1),101-108.</p><p>[11] V. J. Lopez, V. A. Villagra and J. Berrocal,"Applyin...</p></li></ul>

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