Ontology Based Personalized Service in E-markeplaces: A Case Study in a Used Car Matching System C.K. Lee1 and Dickson K.W. Chiu2, Senior Member, IEEE 1 Department of Computer Science and Engineering, The Hong Kong University of Science and Technology 2 Dickson Computer Systems, 7 Victory Avenue, Homantin, Hong Kong email: [email protected], [email protected] Abstract In order to provide effective personalized recommendations, the understanding of products as well as the users’ preferences is crucial and this requires domainspecific knowledge. Recently, ontologies have been developed in various business domains with the recent maturing of the Semantic Web technologies, which can be applied for this purpose. In this paper, we present our enhanced meta-model to address this problem. To demonstrate the applicability and effectiveness, this paper present an application of the Semantic Web based technologies to a Used Car Matching System (UCMS) in an e-marketplace as a case study. We present the ontology for modeling used cars with RDF (Resource Description Framework) and RDF Schema, together with some sample coding and information model to demonstrate the implementation. 1. Introduction Recently, Semantic Web technologies [7][9] have been maturing to make e-commerce interactions more flexible and automated. The Semantic Web provides explicit meaning to the information available on the Web for automated processing and information integration based on the underlying ontology. Ontology defines the terms used to present a domain of knowledge that is shared by people, databases, and applications. In particular, ontology encodes knowledge possibly spanning different domains as well as describes the relationships among them. Ontologies have also been developed in various business domains. The trading of second-hand product is becoming more and more popular over the web. However, searching are often ineffective because matchmaking functions are still preliminary and services supporting domain-specific product knowledge are rare. This motivates our study on the use of semantic web for such applications. Based on the discoveries our earlier work [3] on using ontology for the elicitation of negotiation requirements and the formulation of efficient negotiation processes, we adapt them to become the fundamental effective support for the elicitation of trade requirements in e-marketplaces. Ontology provides the key knowledge about the interrelationships among the issues and alternatives of the traders’ requirement so that object-oriented analysis of them can be streamlined and possibly automated in an emarketplace. In this paper, we illustrate the applicability of our model semantic web based technology for the trading of second-hand cars. The rest of this paper is organized as follows. Section 2 discusses background and related work. Section 3 presents a concept model of an e-marketplace based on ontology. Section 4 introduces an overview of the system. Section 5 presents some details of the application of Semantic Web technologies of the implementation. Section 6 summarizes the paper with the advantage of our approach and our future work direction. 2. Background and Related Work Analysis by Forrester [10] estimates that 18% of global exports will flow online by 2004 and that cross-border eMarketplace trade will surpass $400 billion. Despite technical challenges, e-Marketplaces have emerged to be important trading platforms in recent years. The popularity of e-Marketplaces is largely attributed to their improvement in economic efficiency, reduction in margins between price and costs, and speeding up complicated business deals. However, there are also drawbacks when online eMarketplace are implemented and used for business transaction. Obstacles such as boardroom conflicts, integration hurdles, and unprofitable business models still have to be overcome [10]. Due to its immaturity, e-Marketplaces are often industry-specific with competitors joining forces to aggregate their purchasing power operating both horizontally and vertically [14]. Because of cost, organizations in all sizes are expected to purchase a significant amount in order to gain benefit by adopting e-Marketplaces in their procurement process. Organizations dedicated to it still have to modify its business process in a number of areas including changing internal procurement processes, integrating e-Marketplaces within internal systems, purchasing B2B applications, and paying e-Marketplace transaction fees. On the other hand, although Semantic Web technologies are maturing, ontology standards are still forming [9]. Challenges remain for reusing available ontological information and researchers focus on information integration. In the past years, there are different standardized languages proposed. For example, the DARPA Agent Markup Language (DAML) [6] is an ontology language based upon the Resources Description Framework (RDF) [17]. DAML-S was designed to serve as the basis for representing descriptions of inverses, unambiguous properties, unique properties, lists, restrictions, cardinalities, pairwise disjoint lists, and data types. The Web Ontology Language (OWL) [21] is an eXtended Markup Language (XML) proposed by the World Wide Web Consortium (W3C) for defining Web ontologies. OWL ontology includes descriptions of classes, properties, and their instances, as well as formal semantics for deriving logical consequences in entailments. Edgington et al. [8] point out that adopting ontology can facilitate knowledge sharing. He et al. [12] have surveyed a large number of researches on agent-mediated e-commerce and point out that semantic interaction and personalization are the main problem. However, at the time of writing and as far as we know, no other publications in major journals detail the applications of ontology in e-marketplaces. Cho [5] studies various requirements of negotiation support in e-Marketplace and evaluates some popular eMarketplaces. Despite rapid automation of the other phases of e-commerce transactions, negotiations are often done by using emails or traditional manual communication technologies such as phones or face-to-face meeting, causing serious overhead costs. The work further provides a framework for designing and evaluating a multidimensional auction model. However, these studies do not cover different modes of negotiation comprehensively in one complete framework nor negotiation based on econtracts. Yen et al. [19] propose an intelligent clearinghouse approach that supports both data and textual information about dynamic markets during negotiation, and develops an agent-based prototype Virtual Property Agency. Negotiation support is mostly limited to simple bidding functions. There is a lack of general support for bargaining like the proposed mechanism in this paper. Schoop and Quix [18] present the negotiation process as the exchange of contracts between the parties in an eMarketplace. The contract contents are presented as extensible semi-structured documents. During the negotiation process, the contract evolves over time until a final agreement has been reached or the negotiation is terminated. All these works do not consider traders’ requirements elicitation or other fundamental mechanisms relating to the effectiveness of negotiation. Yu and Mylopoulus [20] consider the dependencies of business goals but not down to the practical details of traders’ requirements elicitation. Phelps et al. [16] suggest the use of ontology for agent-based negotiation with a focus on the heuristics of bidding strategies of auctions instead of negotiation plan for bargaining support. Lee [13] points out the use of semantic value and ontology servers with the help of context agents to avoid inconsistency in the exchange of offers during e-negotiation, but not further for requirements elicitation. Ontology negotiation enables users to cooperate in performing an activity based on different ontologies [2]. Modeled on the patterns of successful human communication, ontology negotiation consists of a series of interpretations and clarifications intended to locate common vocabulary and assumptions [1]. However, these studies concerned with how consensus of ontologies can be arrived at. They do not consider further how an agreed ontology can help the requirements elicitation as well as the formulation of matchmaking, recommendation, and negotiation processes in general, as our novel attempt in this paper. 3. E-marketplace Conceptual Model and our Methodology In this section, we extend the conceptual model of Chiu et al. [3] for an e-marketplace and an overall process model as a methodology to support all the main business processes (instead of just negotiation), starting from traders’ requirement elicitation, to matchmaking, recommendation, and negotiation using ontology. 2..n Negotiation Trader Ontology n Matchmaking Auxiliary Concept Base Concept Recommendation 1..n 1..n 1..n 1..n Task 1 1 1 evaluates 1..n Offer Accepted Offer n resolves drives 1..n Issue 1 maps to formulates 1 Decision Plan 1 precedes Concept n n 1..n n 1..n n indivisibly relates to 1..n 1..n Alternative Value Accepted Alternative Value Figure 1. Conceptual Model of an ontology-based e-Marketplace in UML Class Diagram Figure 1 presents a conceptual model for an emarketplace in the Unified Modeling Language (UML)[15] class diagram based on ontology. Traders are involved in the three main business processes of an emarketplace, namely, matchmaking, recommendation, and negotiation. Each process is made of up tasks, each of which aims at resolving a requirement issue or a collection of co-related issues. The elicitation and evaluation of these issues is facilitated by mapping each of them to a set of concepts and their relationships based on an agreed ontology. If an issue is mapped into exactly one concept in an ontology, we call this concept a base concept. However, if an issue can break down into several concepts according to an ontology, we call these concepts auxiliary concepts. In this way, the agreed ontology help the traders to elicit their requirements before evaluating and making their decisions, that is, identify the inter-relationships among the issues and concepts, as well as possible alternatives for the issues (as explained in Section 4). A decision plan can thus be formulated based on the relationships across these concepts. The plan presents a strategy to drive and organize various tasks in the emarketplace. The e-marketplace’s intelligent software considers multiple offers and bids in a matchmaking task or a recommendation task until results are found in is. On the other hand, a task for e-Negotiation represents some work that needs to be executed by a set of parties that can be a negotiator, or even a program such as Negotiation Support Systems (NSS) to resolve some specific issues. Trader select agreed relevant ontologies for each collection of co-related issue [not consistent] [consistent] System maps issues into ontology concepts System derive concept relations System check consistency of issues & concepts Trader identify issues System identifies alternatives System formulate decision plan [need to identify new issues] Requirements elicitation phase Requirements elicitation phase [need to revise tradeoff model] [need to identify new issues] System creation of agreement [all issues are resolved] System supported trader negotiation [negotiation [quit target chosen] negotiation] [accept offer] Trader post (revised) Trader product preferences as offer selection [reject all matches/ recommendations] System performs recommendation [match not found] System performs matchmaking Trader specifies alternative values of issues Decision phase [match found] [trader change requirements] Decision phase Figure 2. Ontology Based e-Marketplace Process Model in UML Activity Diagram Figure 2 depicts (in the notation of UML activity diagram) the overall process model for an e-marketplace as well as our proposed methodology for the elicitation of traders’ requirements based on ontology. The overall emarketplace business process is driven by our conceptual as described in the previous sub-section. Traders have to participate in each constituting activity of the process, which consists of two major phases: requirements elicitation phase and decision phase. The requirements elicitation phase is based on the most common and logical way of analyzing the issues with ontology (as detailed in Section 4). We do not preclude other possible sequences for a feasible decision plan formulation. In particular, decision plans once elicited can be stored in a repository for reuse and adaptation. That means, traders may just pick a decision plan from the repository and starts right away. Therefore, our approach is suitable for e-marketplaces of more complicated B2B e-commerce, where semi-structured decision making are often repeated and efficiency is also important. The decision phase is also heavily supported by the emarketplace, which first suggests matching offers, and then if not found, recommend those near misses for selection or potential negotiation. Note that only through mutual concessions can the negotiation process reach an agreement. This process eventually leads either to a successful creation of an agreement or the trader may insist in posting the requirements as a new offer in the emarketplace for other traders, without accepting any existing ones. The following steps further elaborate on our methodology. In Phase 1, the Requirement Elicitation Phase, a trader has to determine the issues of requirements. 1. At the same time, the trader selects a commonly agreed ontology from the e-marketplace’s ontology to help the elicitation of requirements. 2. The requirements are related to the concepts in the selected ontology. 3. The system checks all the dependencies of concepts that constitute the requirements from the (refined) ontology map. Mutually dependent clusters of concepts determine the indivisible groups of requirements that have to be considered together so that effective tradeoff can be evaluated. 4. The system checks the consistency of all the concepts, issues, and their dependencies [4]. 5. For a consistent plan, the system can proceed to elicit the possible alternatives; otherwise we have to reiterate from step 3. 6. According to the dependencies, the system can formulate a precedence graph of the requirements and requirements groups. Based on the precedence graph, an efficient decision plan can be determined. In Phase 2, the Decision Phase, not only does the effective decision plan help systematic stepwise evaluation in match-making (instead of considering an exponential number of alternative combinations) and recommendation, the progress of a negotiation can also be visualized and exploited with the maximum possible concurrency. 7. The system searches for the matching offers based on the trader’s preference and attempt to rank them for the trader to choose. The trader may then either (i) accept any matched offers or (ii) chance his reservation price and attempt a negotiation with those offers in order to seek for a more favorable one. 8. If no matching offers are found, the system identifies near misses and also attempts to rank them for the trader to choose. The trader may (i) change his mind to accept a near miss, or (ii) choose a near miss for negotiation. 9. During negotiation, the system supports the user to make and evaluate offers / counter-offers based on the decision plan (from step 6) in a negotiation session as follows [3]. o Each negotiation cycle starts with the identification of a set of interrelated requirement issues to be next negotiated, according a negotiation plan based on that from step 6. o Each party will then prepare the reservation alternatives (reservation price) of these issues. After 8 4 5 9 Sell Agent (SA) 10 3 The system comprises two main applications. One is for users who wanted to buy a car, the Buy Agent (BA). The other one is for users who wanted to sell a car, the Sell Agent (SA). The application requires a user to identify oneself upon the first time usage. The ID is stored in an RDF file, with attributes like, name, phone number, address, email, and identity card number. When a user submits a query to the BA, the application would return a list of cars for sale, and the list could be sorted and browsed sorted by year, price, location, and availability, etc. Such information has been returned from a web spider continuously searching the web for RDF files. The SA would ask the user for more information about the car to be sold and the information is store in another car RDF file made available to the web. This car RDF file contains the seller’s id and the details of the car such as type, manufacturer, model, picture, price, and description. To further support the understanding of car models, we use RDF pointers to RDF files containing information about the specific manufacturer and models, such as dealers, resellers, parts, prices, and so on. All the knowledge recorded therefore helps effective matching the personalized recommendations. Buy Agent (BA) 6 4. System Overview 4.1. UCMS System workflow 7 that, they may either make an offer to or wait for some offers from counterparties. o If a party is not satisfied with the (counter-) offer, another counter-offer or a failure message will be received. o A negotiation cycle finishes successfully if an acceptance notification of previous (counter-) offer is received. o Finally, the negotiation process succeeds when all issues have been successfully negotiated. An agreement is successfully created when all issues have been resolved. o However, as the traders may relax their requirements during the negotiation process, some other offers in the e-marketplace may satisfy one or both of them and therefore cause them to quit the negotiation process. This is an extension to the approach of Chiu et al. [3]. 10. In step 7 to 9, the trader can always quit the process, insist on a different requirement, post it to the emarketplace, and wait for some other traders’ responses instead. Should new requirement issues arise in the decision phase (say, due to incomplete specification), the trader can repeat from step 2 to analyze the new issue and its relationships to the existing ones. In real-life, the formulation of a decision plan may involve several iterations. This reflects the traders may not be able to understand all the inter-relationships among the issues in one shot. Resource Detection Agent, (RDA) Purchase & Sell order Directory 2 Resource RDF + XML 1 Figure 3. UCMS workflow Figure 3 further depicts the UCMS system workflow. The Resource Detection Agent (RDA) is the programming entity that looks up all the resources and through the Sell Agent (SA) to build up the car to be sold list (Step 1-3). The Buy Agent (BA) is the programming entity that will be involved by the users who want to buy cars. The BA will then transfer the requirements to the RDA and store the information into the buy list. Then RDA will return a subset of the sell list that matches the criteria placed in the buy order back to the BA (Step 4, 5). The BA will then ask the SA about further information that the user would like to obtain (Step 6, 7). Negotiation will be carried out between BA and SA (Step 8). If the trade is successful, the BA will remove the buy requests (Step 9). At the same time, the SA will also remove the sell order from the purchase requests (Step 10). 4.2. Service model Figure 4 shows an overview of the service model. It should be noted that the UCMS mainly provides matchmaking services (i.e., the blue items in Figure 2). However, different topologies are possible and additional services could be implemented or customized. Thus, this approach is applicable to other business domains generally. Car sell Search car Negotiate Order car Fulfillment Provide car information Provide contact information Provide payment information Provide shipment information Figure 4. UCMS service model 5. Application of Semantic Web Technologies 5.2. RDF XML Format Example 5.1. Ontology for UCMS Figure 8 and 9 illustrate how user and car information are coded into RDF files, respectively. Figure 5 illustrates the car ontology, which features the model of car. Thus, the car is fully described by the ontology and can be searched by its feature. To match the buy requests (see Figure 6) and the sell requests (see Figure 7) of used cars, we use OWL DL classification to relate the specific domains, such as the color relation or the price relation of the two domains. Also based on the classification, our framework provides a way to express the preferences between terms by using the priority property. So, by this method, we can indicate which result to be considered for the matching. Mand atory Car ry dato Man Car Body Man dato Optional ry Transmission Altern y da tor Pulls trailer Alte rna tive tive Altern ative ry Ma n dato Red ti ative Man Color a ern Alt ve Engline Alte rna Automatic Manual Electric No. of seats Alte rna Altern ativ tive Blue e Alternative 5-seats 7-seats Gasoline Name Peter Pan Phone 8109922355 May Chan … 8186655223 … Vehicle Important Description Priority Description Property No. of seats color Price Model number Figure 6. Ontology of Buy Vehicle UCMS Vechicle for sale Seller resource ID Business car Sport car Family car No. of seats Made Year color Price Model number Figure 7. Ontology of Sell Vehicle Identity A8823560 [email protected] K7749521 … … Figure 8. User information Type Light Goods Vechicle Model Toyota Picture Mytoyota.jpg Price 60k Private Car Honda Hondacivic.jpg 35k … … … … <?xml version="1.0"?> Made Year Email [email protected] <?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:ucms_person="http://www.ust.csit600f/ucms_person#"> <rdf:Description rdf:about="http://www.ust.csit600f/ucms_person/ Peter Pan "> <ucms_person:phone number>810-9922355</ucms_person:phone number> <ucms_person:address>No 1, Tai Ming Estate, TT, HK</ucms_person:address> <ucms_person:email>[email protected]</ucms_person:email> <ucms_person:identity>A8823560</ucms_person:identity> </rdf:Description> <rdf:Description rdf:about="http://www.ust.csit600f/ucms_person/ May Chan"> <ucms_person:phone number>818-6655223</ucms_person:phone number> <ucms_person:address>Room 8, Hall 1, UST, HK</ucms_person:address> <ucms_person:email>[email protected]</ucms_person:email> <ucms_person:identity>K7749521</ucms_person:identity> </rdf:Description> ... </rdf:RDF> Figure 5. Ontology (car) Buyer resource ID Address No 1, Tai Ming Estate, TT, HK Room 8, Hall 1, UST, HK … <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:ucms_car="http://www.ust.csit600f/ucms_car#"> <rdf:Description rdf:about="http://www.ust.csit600f/ucms_car/<?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:ucms_car="http://www.ust.csit600f/ucms_car#"> <rdf:Description rdf:about="http://www.ust.csit600f/ucms_car/Light Goods Vechicle"> <ucms_car:model>Toyota</ucms_car:model> <ucms_car:picture>Mytoyota.jpg</ucms_car:picture> <ucms_car:price>60k</ucms_car:price> <ucms_car:remark> <rdf:Bag> <rdf:li>Auto</rdf:li> <rdf:li>4 safety-bag</rdf:li> <rdf:li> 8-seats</rdf:li> </rdf:Bag> </ucms_car:remark> </rdf:Description> <rdf:Description rdf:about="http://www.ust.csit600f/ucms_car/Private Car"> <ucms_car:model>Honda</ucms_car:model> <ucms_car:picture>Hondacivic.jpg</ucms_car:picture> <ucms_car:price>35k</ucms_car:price> <ucms_car:remark> <rdf:Bag> <rdf:li>Manual</rdf:li> <rdf:li>V-tec engine</rdf:li> </rdf:Bag> Remark Auto, 4 safety-bag, 8seats Manual, V-tec engine … Order Received Begin Enquiry Received Check System Config Prepare Quotation Send Quotation Req Extra Info System Integrator Prepare Service Deliver & Install Payment Received End Request Extra Info Sell Integrated System </ucms_car:remark> </rdf:Description> ... </rdf:RDF> Send Extra Info Begin Order Missing Parts Assemble System References Test Install Software [1] Prepare Service Figure 9. Car information Begin 5.3. RDF Schema Update Catalog [2] End Receive Part Info Updates Figure 10 shows the schema about the resource of “Toyota” and “Honda” is subclass of “car”. <?xml version="1.0"?> <rdf:RDF xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xml:base= "http://www.ust.csit600f/ucms_car#"> <rdf:Description rdf:ID="car"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> </rdf:Description> <rdf:Description rdf:ID="toyota"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> <rdfs:subClassOf rdf:resource="#car"/> </rdf:Description> <rdf:Description rdf:ID="honda"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> <rdfs:subClassOf rdf:resource="#car"/> </rdf:Description> ... </rdf:RDF> [3] [4] [5] [6] [7] [8] [9] Figure 10. RDF Schema [10] [11] 6. Discussion and Conclusion [12] The real power of the Semantic Web can only be realized when a large variety of services that collect Web content from diverse sources, process the information, and exchange the result with other programs. The effectiveness of software agents will increase exponentially as more machine-readable web content and automated services and other collaborating agents become available. The Semantic Web is not just a tool for conducting individual tasks that we have discussed so far. In addition, if properly designed, the Semantic Web can assist the evolution of human knowledge over the Internet as a whole. Then, resources can be modeled and standardized to be understood and utilized. In the Semantic Web, with well defined ontology, it can provide semantic links between and within resources to model. Thus, information and knowledge can be standardized, processed, and exchange effectively. 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