An Integrated Information Platform for Intelligent Transportation Systems Based on Ontology

Transcription

1 An Integrated Informaton Platform for Intellgent Transportaton Systems Based on Ontology Jun Zha, Zhou Zhou, Zhman Sh and Lxn Shen School of Economcs and Management, Dalan Martme Unversty, Dalan , P.R. Chna Abstract. In semantc web envronment, the ntegraton of transportaton nformaton systems develops toward semantc ntegraton. Ontology facltates the ntegraton of heterogeneous data sources by resolvng semantc heterogenety among them. In ths paper, we propose the system archtecture of ntegrated nformaton platform for ntellgent transportaton systems (ITS) based on ontology, ncludng three man layers: dstrbuted heterogeneous data source layer, nformaton ntegraton layer, and applcaton system layer. Its core s the nformaton ntegraton layer ncludng the ontology server and the ntegrated database. Key technque appled n the ontology server s studes. Frstly, the doman ontology model for transport system s presented. Then we dscuss the approach to semantc ntegraton of XML documents based on ontology. At the end we conclude that ontology s a good tool to ntegrate traffc nformaton among varous heterogeneous traffc management systems on semantc level. Keywords: Applcaton ntegraton, Data ntegraton, Ontology, Enterprse nformaton archtecture, Enterprse nformaton ntegraton (EII), Enterprse nformaton systems (EIS), Semantc ntegraton, Intellgent transportaton systems (ITS) 1. INTRODUCTION Intellgent Transportaton System (ITS), a developng conformaton of transportaton system n the nformaton tmes, has been ntegratng a varety of advanced technologes, especally nformaton technology [1]. Now many knds of urban traffc management systems are establshed on ther own data storage style (such as database or data fles), whch operate the data source drectly, lackng data share and exchange. It s vtal to solve that how to share and exchange the data among varous transportaton management systems, and how to utlze the data suffcently and mprove the level of urban traffc management. It s vtal to solve the problems that how to share and exchange the data among varous transportaton management systems and how to utlze the data suffcently to mprove the level of urban traffc management. It s necessary to establsh an Integrated

2 788 Jun Zha, Zhou Zhou, Zhman Sh and Lxn Shen Informaton Platform (IIP) for ITS, whch processes varous data from dfferent traffc data sources located n varous traffc management systems. It can serve as a brdge of data share and exchange among dfferent applcaton systems and data sources, whch provdes traffc management decson-makng support, nformaton servce functon etc [2-4]. We found some proects smlar to the ntegrated nformaton platform n some countres. In 2001, the MOST (Mnstry of Scence and technology) of Chna apponted ten ctes as ITS demonstraton ctes, ncludng Beng, Shangha, Guangzhou, Shenzhen etc. The ntegrated nformaton platform s an mportant part n the ITS plannng of each cty. Meanwhle many scholars and some companes have begun the research and development of the ntegrated nformaton platform and acheved some valuable results. In other countres, such as England, Sngapore, Amerca, etc, there are also some smlar research and mplement proect as IIP for ITS [5]. IIP for ITS manly solves the heterogenety among dverse nformaton sources. Amt Sheth [6] has classfed heterogenety nto four categores: system, syntax, structure and semantc. The system heterogenety ncludes hardware and operatng systems; the syntax heterogenety ncludes dfferent languages and data representatons; the structure heterogenety ncludes dfferent data models; and semantc heterogenety ncludes the semantcs of user s nformaton request and those of nformaton sources. Many of the heterogenety wll overcome f XML/DTD s gong to be adopted for data publshng, whch s used n present research works. However the semantc heterogenety remans [7]. In the WWW envronment, the ntegraton of current nformaton systems turns to semantc level due to the more dversty and heterogenety of data. The semantcs of dverse nformaton sources are captured by ther ontologes,.e., the terms and relatonshps among them. Ontologes are emergng as an mportant tool for constructng sharable and reusable knowledge repostores and supportng ther nteracton [8-10]. In ths paper, we present an IIP system archtecture based on ontology to acheve the semantc ntegraton for ITS. The remander of the paper s structured as follows. In secton 2 the IIP system archtecture s descrbed. In secton 3 the doman ontology model for transportaton system s ntroduced. In sectons 4 we dscuss the approach to semantc ntegraton of XML documents based on ontology. Fnally, n secton 5 we present some conclusons and ndcate drectons for future work. 2. IIP SYSTEM ARCHITECTURE BASED ON ONTOLOGY IIP forms an abstract homogeneous envronment for the applcaton system through ntegratng the dstrbuted heterogeneous subsystems and provdng transparent servce based on semantc for users. The system archtecture of IIP s shown as Fgure 1, ncludng three layers: dstrbuted heterogeneous data source layer, nformaton ntegraton layer, and applcaton system layer.

3 An Integrated Informaton Platform for Intellgent Transportaton Systems Based on Ontology Dstrbuted Heterogeneous Data Source Layer The dstrbuted heterogeneous data source layer s manly conssted of varous traffc management systems, such as traffc sgnal control system, emergency management system, publc transport management system, vdeo montorng system, and varable message sgn system etc, whch are the man data sources of IIP. The compatble data sources of IIP nclude relatonal database, real-tme database, web data, XML documents etc. As the data sources of IIP, varous traffc management systems can share and exchange data through ntegrated transportaton nformaton platform on semantc level. The man types of traffc data are shown n Table 1. Table 1. The Man Knds of Traffc Data Space data Type geographcal Content The cty transportaton concerned spatal data and spatal attrbute data, whch nclude the elements of cty-road-net such as road, crossng and park. Traffc nfrastructure data Traffc management operaton data Hstorcal data Other concerned data Hardware nfrastructure data exclude space geographcal data, whch nclude communcate, examnaton and control nfrastructure n transportaton. The real-tme data of traffc flow, traffc sgnal control, electrc polte, equpment fault etc. The hstorcal data of traffc flow, accdent and peccancy. The transportaton concerned data (such as transfer nfo, weather report and schedules) and other traffc servce concerned yellow page nformaton (such as hotel, tran, servce staton etc). 2.2 Informaton Integraton Layer The nformaton ntegraton layer s the key of ntegrated nformaton platform, whch manly ncludes two parts: ontology server and ntegrated database. The man functons of ontology server are as follows: 1. To acheve the semantc upgrade of data sources. The server uses the software reverse engneerng approach to extract an ntal ontology from gven data sources and ther applcaton programs. Ontology desgners wll refne ths ntal ontology. Thus every data source generates own local ontology. Ontology reasonng then s used to check ontology consstency and to merge ontologes to obtan the global ontology, whch provdes the user access to the data wth a unform query nterface to facltate the formulaton of a query on all the data sources. The server ncludes the mappng database, whch records the mappng nformaton between ontologes, and ontology and data sources. These mappngs are prmtve concept mappngs.

4 790 Jun Zha, Zhou Zhou, Zhman Sh and Lxn Shen 2. To acheve the semantc annotaton to the ntegrated database. A set of XML schema or DTDs derved from the global ontology. The global ontology defnes the semantcs of the terms used to model the data. The set of XML schema or DTDs s used to mark up the data n the ntegrated database. When an applcaton or agent requres data from the nformaton platform, t wll construct a set of queres over the encoded data source. If the applcaton or agent does not understand the tags of the XML schema or DTDs assocated wth the data, t wll query the ontology server. The ontology server s capable of mappng terms, returnng relatonshps between terms and attrbutes assocated wth the terms. 3. To manage the ontology. Ontology edtor and browser are tools that allow users to vsually manpulate ontologes. The edtor and browser dsplay ontology n a treelke structure wth nodes denotng concepts. The detals of the concepts can be dsplayed by hghlghtng nodes. In the edtor mode, defntons can be modfed, nodes can be added or removed. Ontology relatonshps can also be dsplayed. In secton 3 and secton 4 we dscuss the ontology model and ntegraton approach, whch are the key technque appled n the ontology server. 2.3 Applcaton System Layer Achevng the semantc ntegraton, the IIP can deeply, synthetcally utlze varous traffc data and nformaton. Based on a large amount of traffc data stored n IIP ntegrated database, wth the Data Fuson, Data Mnng technology, some applcaton systems may be developed, such as nformaton servce system, decson-makng support system etc, to provde nformaton servce for traffc managers, travelers and other people. Through these ways, traffc data and nformaton can be used more effcently, and the ntellgent level of urban traffc management can be mproved as well. 3. THE DOMAIN ONTOLOGY MODEL FOR ITS Gruber [11] defnes ontology as an explct specfcaton of a conceptualzaton,.e. an abstract and smplfed representaton of real-world enttes. An ontology can be vewed as a model of a doman that defnes the concepts exstng n that doman, ther propertes and the relatonshps between them and s typcally represented as a knowledge base. An ontology ( O ) organzes doman knowledge n terms of concepts ( C ), propertes ( P ) and relatons ( R ) and can be formally defned as follows. Defnton (Ontology) An Ontology O s a trplet of the form O ( C, P, R), where:

5 An Integrated Informaton Platform for Intellgent Transportaton Systems Based on Ontology 791 Fgure 1. IIP System Archtecture Based on Ontology for ITS 1. C s a set of concepts defned for the doman. A concept s often defned as a class n an ontology. 2. P s a set of concept propertes. A property p P s defned as an nstance of a ternary relaton of the form p ( c, v, f ), where c C s an ontology concept, v s a property value assocated wth c and f defnes restrcton facets on v. Some of the restrcton facets are type ( f t,) cardnalty ( f c ), and range ( f r ). The type facet f t may be any one from the standard data types supported by ontology edtors.e., f t {Boolean, nteger, float, strng, symbol, nstance, class }. The cardnalty facet f c defnes the upper and lower lmts on the number of values for the property. The range facet f r specfes a range of values that can be assgned to the property. 3. R { r r C C Rt} s a set of bnary semantc relatons defned between concepts n O. R t = {one-to-one, one-to-many, many-to-many} s the set of relaton type. A set of basc relatons s defned as R b {,, } whch have the followng nterpretatons: 1. For any two ontologcal concepts c, c C, denotes the equvalence relaton. c c s equvalent to c. The synonym relaton of natural language s c

6 792 Jun Zha, Zhou Zhou, Zhman Sh and Lxn Shen modeled n an ontology usng the equvalence relaton. If two concepts c and c are declared equvalent n an ontology then nstances of concept c can also be nferred as nstances of c and vce-versa. 2. denotes the generalzaton relaton. c c c s a generalzaton of c. When an ontology specfes that c s a generalzaton of c, then c nherts all property descrptors assocated wth c, and these need not be repeated for c whle specfyng the ontology. 3. c c c has part c. In an ontology, a concept whch s defned as aggregaton of other concepts s expressed usng the relaton. Agency Schedule related to synonym Flght Travel Itnerary related to s a has part s a Traveler Tran Tour related to Tourst related to synonym related to s a Passenger Bus Trp Club Fgure 2. Partal Tourst Informaton Servces Doman Ontology The ndvdual nformaton servces are the vtal part of the traveler nformaton servces, whch assemble correlatve nformaton from mult-data-sources (weather bureau, news, agency etc.) for satsfyng the personal needs of travelers. The typcal applcaton s the travel nformaton afforded for the tourst, n whch the partal travel doman ontology s shown n Fgure 2. The man concepts nclude tourst, agency, trp, tnerary etc. The concepts can be related n varous ways. The four most commonly used are synonym (equvalent), s-a (generalzaton), whole-part (has part) and related-to where the semantcs of the frst three are descrbed above. Related-to s used for generc assocatons between concepts. In RDFS the concepts of doman ontology are represented as follows: <rdfs:class rdf:id= Agency ></rdfs:class> <rdfs:class rdf:id= Travel product ></rdfs:class> <rdfs:class rdf:id= Tour > <rdfs:subclassof rdf:resource= #Travel product /> </rdfs:class> The relatons are represented as follows: <rdf:property rdf:id= has part > <rdfs:doman rdf:resource= #Tour > <rdfs:range rdf:resource= # Itnerary >

7 An Integrated Informaton Platform for Intellgent Transportaton Systems Based on Ontology 793 </rdf:property> <rdf:property rdf:id= synonym > <rdfs:doman rdf:resource= #Tour > <rdfs:range rdf:resource= # Trp > </rdf:property> The property s represented as follows: <rdf:property rdf:id= Agency Name > <rdfs:doman rdf:resource= #Agency > <rdfs:range rdf:resource= #Strng > </rdf:property> The nstance of a concept s represented n RDF as follows: <rdf:descrpton rdf:id= Dalan Agency > <rdf:type rdf:resource= #Agency /> <Agency Name>Dalan Agency</Agency Name> </rdf:descrpton> 4. THE APPROACH TO SEMANTIC INTEGRATION OF XML DOCUMENTS BASED ON ONTOLOGY XML s becomng the standard for data nterchange on the web and a web-frendly technology for IIP nformaton exchange [4]. However, XML and ts schema languages do not express semantcs but rather structure, such as nestng nformaton [7]. RDF (Resource Descrpton Framework) and RDFS (RDF Schema) s a data model and support mechansm for representng meta-data of schemas. XML and RDF are the current standards for establshng semantc nteroperablty on the Web. RDF better facltates nteroperaton because t provdes a data model that can be extended to address ontology representaton technques [12]. In ths secton, we dscuss the ntegraton approach of XML sources nto the global ontology. The ontology ntegraton process contans two steps: schema transformaton and ontology mergng. In the frst step, we use RDFS to model each XML source as a local RDF ontology to acheve a unform representaton bass for the ontologymergng step. The key operaton s the preservaton of the nestng structure of the XML documents. In the second step, we merge all the local RDF schemas to generate the global ontology. In ths process, addtonal doman-related knowledge (e.g., nhertance) may be ntroduced. Durng the mergng process, a mappng table s produced to contan the mappng nformaton between the global RDF ontology and local RDF ontologes. 4.1 Schema Transformatons Takng nto account XML elements, attrbutes and ther relatonshps, the transformaton from XML to RDF can further nclude element-level transformaton and structure level transformaton.

8 794 Jun Zha, Zhou Zhou, Zhman Sh and Lxn Shen The element-level transformaton defnes the basc classes and propertes of the local RDF ontology accordng to the transformaton correspondences shown n Table 2. No new RDF metadata needs to be defned here because rdfs: Class and rdfs: Property s enough for the specfcatons of classes and propertes. The structure-level transformaton encodes the herarchcal structures of the XML schema nto the local RDF ontology. The encodng nvolves two relatonshps: element-attrbute relatonshp and element-subelement relatonshp. Followng the element-level transformaton, t s natural to encode the element-attrbute relatonshp as a class-to-lteral relatonshp, and the element-subelement relatonshp as a class-toclass relatonshp n RDFS. We defne a new RDFS predcate rdfx: contan to represent class-to-class relatonshps. Specfcally, we add a new property wth ts doman beng one class (converted from the parent element), ts range beng the other class (converted from the subelement), and ts name beng rdfx: contan. Table 2. Element-level Transformaton XML Schema concepts Attrbute Smple-type element Complex-type element RDF Schema concepts Property Property Class 4.2 Ontologes Mergng The process of ontology mergng takes multple local ontologes (encoded n RDFS) as the nput and returns a merged ontology as the output. Ontology mergng and ontology algnment are wdely pursued research topcs. In ths paper we do not ntend to ntroduce a new technque for ontology mergng. Instead, we utlze exstng technques to generate the ntegrated ontology from the local ontologes. In partcular, we use the approach that provdes the followng functonaltes [13]: 1. Mergng of classes where multple conceptually equvalent classes are combned nto one class. 2. Mergng of propertes where multple conceptually equvalent propertes of a class are combned nto one property. 3. Mergng relatonshps between classes where conceptually equvalent relatonshps from one class c 1 to another class c 2 are combned nto one relatonshp (.e., an RDF property takng c 1 as ts doman and c 2 as ts range). 4. Copyng a class and/or ts propertes f the same or equvalent class/property does not exst n the target ontology. 5. Generalzng related classes nto a more general superclass. The superclass can be obtaned by searchng an exstng knowledge doman or reasonng over a thesaurus.

9 An Integrated Informaton Platform for Intellgent Transportaton Systems Based on Ontology 795 Rout Bus Route Lght-ral Route Road Publc Transportaton Route Roadway Node Routeway Node Staton Node Road XML Data Structure Global Ontology XML Data Structure Fgure 3. Global Ontology and XML Documents Fgure 3 gves an example, n whch the elements Rout and Routway of two XML data structures are semantcally ntegrated to the Publc Transportaton Route concept of the global ontology. 5. CONCLUSIONS Ontology-based ntegrated nformaton platform s motvated by the followng propertes: 1. Precse descrpton of data and nformaton. IIP uses standardzed terms of the ontology and ts nherent semantcs to provde a formal descrpton of ts data. Queres based on the unform semantcs are less prone to msnterpretaton of local nformaton semantcs. 2. Dynamc support for multple contexts or nterpretaton of data. Tradtonal schema-based database ntegraton of systems requres costly updates to accommodate new semantcs. Usng the terms of ontology as meta-constructs or meta-attrbutes allows proper dynamc nterpretaton of the dfferent contexts. Our further researches lay on the automatc ntegraton among dfferent doman ontology, especally among the transportaton ontology and other doman ontology such as the GIS ontology and urban ontology. ACKNOWLEDGEMENTS The authors would lke to thank peer revewers for commentng ths artcle. Ths work s supported by the Natonal Natural Scence Foundaton of Chna (Grant NO ).

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