Description Logics: a Modelling Support for Automatic Cataloguing in ...

Description Logics : a Modelling Support for Automatic Cataloguing in E-Commerce F.L.Soualmia Laboratoire d’Informatique (LIMOS) – Université Clermont Ferrand II. Complexe Scientifique des Cézeaux, 24 avenue des Landais – 63177 Aubière – France. Email : [email protected], Tel : (+33) (0) 4 73 40 77 68, Fax : (+33) (0) 4 73 40 74 40.

Currently, the electronic commerce (E-Commerce) knows an important growth, which results in the emergence of many commercial sites on the Internet network. The web sites of the providers propose to the consumers offers of products or services in electronic catalogues. Ontologies are generally used for the purpose of modelling the catalogues. In order to facilitate to the users the search of products or services, the commercial companies that are offering the same type of products gather their sites in electronic market places (E-Market Places) in which the transactions are guided by the use of a global catalogue that contains all the offers. We analyse in this paper the problems related to the E-Commerce, particularly the management problem of the electronic catalogues in the E-Market Places. For modelling the electronic catalogues, we propose a logical approach, based on Description Logics (DLs) issued from knowledge representation. We show how the reasoning services provided by knowledge representation systems based on DLs can support the operations of automatic cataloguing.

1.Introduction The electronic commerce (E-Commerce) currently knows an important growth. The Internet network contributes to this growth at several levels by increasing the speed and the effectiveness of the commercial transactions, by improving the consumer services and by reducing the transaction costs [27]. More and more purchases are carried out on the Web allowing the development of many commercial sites and many companies in two types of ECommerce: the Business to Consumer (B2C) and Business to Business (B2B) commerce in which the transactions are guided by electronic catalogues [40]. An electronic catalogue is like a database containing information on provider’s products or services proposed by one provider, on its Web site, or by many providers, gathered in electronic market places (EMarket Places) [2] where the consumers can at any moment consult many catalogues. A search engine, operating by key word allows to find a product by simultaneous search in all the catalogues. However, in this new kind of commerce, there are many problems of interoperability and communication between the applications, particularly in the E-Market Places, due to the companies diversity, the commercial practices, the data formats…etc. The principal barrier to E-Commerce is the need of applications for sharing information [42]. A solution is the use of E-Market Places based on ontology [21] for knowledge representation, catalogues classifying and indexing, and users query answering [33]. In this paper we study the problems of E-Commerce, like the catalogues maintenance and services/products updates. We propose an approach based on Description Logics (DLs) [4] for automatic cataloguing. DLs are expressive knowledge representation languages and systems based on DLs have powerful reasoning services. The paper is organised as follows. In section 2 we give the characteristics of E-Commerce and electronic catalogues and identify their problems. Then we give Ontologies [22] advantages in E-Commerce and present in section 3 the DLs and their associated reasoning services, like automatic information classification. Our approach is detailed in section 4 and we conclude in section 5.

2.E-Commerce 2.1.Definitions, systems and problems Electronic commerce (E-Commerce) is defined as being the sale of provider products to a consumer by using the Internet network [1]. It is also a set of commercial and noncommercial transactions via Internet [26]. 2.1.1.E-Commerce types The electronic data interchange (EDI) between companies and administrations has been largely developed during the ten last years. The reduced cost of Internet and its useful use on a large scale allowed its fast integration into small companies [41]. The key factor for the ECommerce development is the ubiquity of information access via Internet, which allows to users many offers browsing around the world. There are three types of E-Commerce [27]: ' The Business to Consumer (B2C): which relates companies and consumers. The consumer can be either a company or an individual that buys a product. In the first case there are no commercial data interchanges between companies. ' The Business to Business (B2B): relates two companies by buying and selling providers’ products or services and also electronic data interchange (EDI). These inter-companies exchange improved performance and productivity in command management. ' The Within Business is a protected Internet network .A company equipped with an Intranet can develop databases allowing to its employees a permanent access to relevant information [27]. 2.1.2.E-Commerce systems and problems Many systems configurations associated to E-Commerce were developed independently from the E-Commerce type [2]. The first form is the Web Mall which is a web site containing links to commercial sites that are offering the same category of products, after having paid the Web Mall (or E-Mall). The second organisation appears as a set of packaged services integrating providers’ information, allowing search, comparisons and links to the products. However, these kinds of services do not support commercial transactions. The third form of organisation is the Electronic Market Place (E-market Place) which is a network allowing transactions between providers and consumers by collecting and updating products data, standardising it for an effective information sharing independently from the source, and answering users requests. However, several problems arise: ' Dispersion of the catalogues: time and resources are required for consulting the providers’ catalogues that propose the same categories of products. ' Different formats are used: each provider has its own catalogue which format is often different from the E-Market Place format. On the data level, the product names can be different. ' Several product classifications: the products are organised into categories and types that can differ according to the providers. ' Textual search engines for products supposes that the user is looking for a product that he knows the name. It can also be done by navigating through the categories and subcategories until finding the product, also when the user knows the product classification. ' Catalogue maintenance is not completely automated.

As a solution to these problems we will show the importance of ontologies in E-Commerce. 2.2.Ontologies in E-Commerce There are many definitions of ontologies [5,23,43]. An ontology is a specification of a conceptualisation [22] that provides a domain knowledge representation composed by terms and relations between terms to be reused and shared between applications [10,21], and allowing communication between systems, knowledge sharing and interoperability between agents, especially for information integration sources [38]. In CORNER [7] ontologies unify the vocabulary of the information sources. InfoSleuth [18] is based on ontological agents related to information sources. In the On2Broker project [14] an ontology is composed by object classes and deduction rules allowing data extraction from Web pages. In PICSEL [20], the integration of heterogeneous information sources is laid by the logical description of domain ontology using Description Logics (DLs). DLs are also used in MOMIS [3] to describe information sources, and for information integration [8]. In E-Commerce, ontologies are used for representing domain knowledge and also for supporting reasoning process and transactions between agents. A shared ontology allows interoperability between commercial agents [42]. The use of a common standard representation of the systems contents is necessarily when several companies communicate and cooperate. For example, a product provider must support several formats and transaction frameworks for integrating an E-Market Place. The principal difficulty encountered by ECommerce is the need of applications for information sharing. Due to their characteristics ontologies are solution for E-Commerce development [42]. In [31] a set of ontologies and a semantic network of products are built. ActiveCatalog provides an environment of catalogue products information for answering users requests by exploiting the domain knowledge. Ontologies are described using Loom [37] and its associated mechanism allows to find products in the electronic catalogues. In [29] a system of electronic catalogues based on ontologies is proposed in a context where several providers co-operate [35]. Infomaster [19] uses ontologies for integrating electronic product catalogues. In [13] the authors propose an example of ontology representation for a cataloguing system of products. In the E-Market Places, like MKBEEM [33] the role of ontologies is more important: ontologies are used to allow commercial agents communication to classify information, to support the multilingual exchanges and also for the automatic cataloguing of products and services. There exist many methodologies [17], tools [16] and languages for ontology construction, like traditional languages (F-Logic [30] , OKBC [11], OCML [39]) and Web languages (Xml [16], XOL [28], RDF [32], SHOE [36], OIL[25]). The choice of the language representation depends on the kind of reasoning services needed in the application. Comparative studies on the ontology languages can be found in [12,15]. In this paper we use an ontological approach for the providers catalogues representation. 2.3.The cataloguing Cataloguing is an operation that allows to a products or services provider to add new offers in his catalogue. Catalogues products are organised in hierarchy. Each product has its own description and properties. Cataloguing is the process of classifying the new product descriptions into the hierarchy. Ontologies are used to formally describe the structure of the catalogue (hierarchy), the used terms (products descriptions) and the relations existing between terms.

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Let consider for example the case of the TZI company which provides products on the Web. Its Web site allows B2B transactions. The vendors have several catalogues structured as a hierarchy of categories. The leafs represent types. A type is a set of products having similar characteristics. It has a set of attributes which values belong to a defined domain. The site allows to visualise the providers catalogues. In addition, a global catalogue, contains all providers classified according to their type and their category. For automatic cataloguing we propose an approach based on DLs, which are equipped with powerful reasoning services. We point out their characteristics in the following section.

3.Description Logics Description Logics (DLs) [4,9] are knowledge representation languages. A terminological system based on DLs has at least two components: a TBox containing intentional descriptions (term equations), and an ABox containing extensional descriptions (assertions). In the TBox, DLs allow a structured representation of terms: a term can correspond to a concept (a set of individuals) or to a role (binary relations between individuals). The terms are declared with terminological axioms built with term constructors. The set of the constructors that will be used depends on the needs of the application. A TBox is a finite set of terminological axioms. One implementation of a DL is the PICSEL system [20] which will be used for the examples in this paper. A “primitive” concept is declared with the terminological axiom (DefPrimConcept B C). Intuitively, B is only defined with necessary conditions. If also sufficient conditions are given, a “defined” concept is declared with (DefConcept B C). In this case, the concept on the left-hand side is “equivalent” to the concept term on the right-hand side. In the TBox, the concepts are organised into a subsumption relationship. In a subsumption relation between two concept, a subsumed concept is the most specific concept and inversely. There are many reasoning and inference services provided by terminological systems based on DLs. In the following we present the language ALN-CARIN [34] associated to the PICSEL system [20] that will be used for automatic cataloguing.

3.1.The language ALN-CARIN 3.1.1.Syntax and semantic The syntactical rules for constructing concepts C and D with atomic concepts A and roles R are as follows: C, D

→

A|(atomic concept) (Top)|(universal concept) (Bottom)|(inconsistent concept) (Not A)|(atomic concept negation) (And C D)|(concepts conjunction) (All R C)|(universal role quantification) (Atleast n R)|(Atmost n R)|(number role restriction)

The meaning of the DL constructs can be given in terms of a set of a theoretic semantics by means of an interpretation. An interpretation is a tuple I=(∆I, .I) where the set ∆I is the interpretation domain, and .I an assignment function associating each concept to a sub-set of ∆I and each role to a sub-set of ∆I×∆I, and such that the following equations are satisfied, with n a number: (Top)I = ∆I (Bottom)I = ∅ I (Not A) = ∆I\AI (And C D)I = CI∩DI (All R C)I = {a∈∆I/∀b,(a,b)∈RI⇒b∈CI} (Atleast n R)I ={a∈∆I/||b/(a,b)∈RI||≥n}1 (Atmost n R)I ={a∈∆I/||b/(a,b)∈RI||≤n} I

I

An interpretation I satisfies the terminological axiom (DefConcept A C)if A =C , and the axiom (DefPrimConcept A C)if AI⊆CI. A TBox is called terminology if no cyclic definitions are present i.e. definitions where a concept name A on the left-hand side occurs (directly or indirectly) in some construct on the right-hand side are not allowed, and for each atomic concept on the left-hand side exactly one terminological axiom is given. The ABox is composed by a set of individuals (noted a,b) and the axioms can appear on two forms: C(a) or R(a,b).The interpretation function .I of I=(∆I, .I) assigns each individual a with an element aI in ∆I. The interpretation I satisfies the axiom C(a) if aI∈CI and the axiom R(a,b) if (aI,bI)∈RI. 3.1.2. Reasoning services There are two kind of reasoning services allowed by knowledge representation systems based on DLs: descriptions and individuals. We are interested here in the reasoning on descriptions:

1

The symbol || || indicates set cardinality.

' Concept satisfiability: a concept C is satisfiable if there exists an interpretation I such that CI≠∅. This test checks if a concept description does not contain inconsistent information. ' Subsumption: a concept C is subsumed by a concept D if CI⊆DI in all interpretation I. ' Equivalence: two concepts C and D are equivalent if CI=DI for all interpretation I. ' Classification: it allows to insert automatically a new satisfiable concept into the hierarchy by placing it on top of its sub-concepts, and under its super-concepts. In the following we show how DLs are well suited for electronic catalogues modelling and for automatic cataloguing.

4. A logical approach for modelling the catalogues We consider in our method that a products catalogue is a hierarchy of objects referenced by term names. Each term corresponds to a concept and concepts are classified by the terminological system using automatic classification. 4.1. Catalogue modelling Let take as example a catalogue of categories, sub-categories and types of products. A product type is a category having attributes that values belong to a set of possible values. The types are indicated in italic in the figure: Catalog Office&Business Books ComputerSupplies Computer ComputerHard UnixServer(Platform,Manual,Price) ComputerSoft Software(Name,Platform,Price) ConsumerElectronics OfficeEnvironment Lighting OfficeFurniture Desk (Manufacturer,Brand,Price) Figure 2. A catalogue example

For modelling the categories and sub-categories we use primitive concepts: Books is a subBooks category of Office&Business. Its description is(DefPrimConcept Office&Business)indicating that the concept (category) Books is included in the concept (category) Office&Business. It will be the same principle for all the catalogue categories. The types are categories having attributes. In this case we will use definitions. For example the type Desks belongs to OfficeFurniture. Its attributes are Manufacturer,Brand and Price. For any instance of Desks, each attribute has only one possible value in the predefined domain values Domain regrouping text, integer, price, boolean…etc. A type attribute is a role relating exactly one time the type to the concept Domain. The Desks description is : (DefConcept Desks(And OfficeFurniture(Atleast 1 Manufacturer)(Atmost 1 Manufacturer)(All Manufacturer Domain)(Atleast 1 Brand)(Atmost 1 Brand)(All Brand Domain)(Atleast 1 Price)(Atmost 1 Price)(All Price Domain)))

The catalogue modelling is as follows:

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The categories : (DefPrimConcept Office&Business Catalog)

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The PICSEL system [20] has two components: OntoClass and OntoQuery. OntoClass (Figure3) allows the concepts hierarchy visualisation inferred automatically by the subsumption concepts algorithm.

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Figure 4.Concepts hierarchy representing the catalogue.

4.2.Catalogue maintenance We consider here many cases of catalogue maintenance. The most frequent cataloguing case is adding a product. It can also generate the need of adding a new product type or a new category, in the case that it does not exist in the catalogue. It is an information classification problem. We suppose that the catalogue is a knowledge base and the new category or type to insert, by automatic classification, is a new concept. $GG D &DWHJRU\ «

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4.2.1.Adding a new type For example we want to add the new product type Chairs in the category OfficeFurniture. Its attributes are Manufact, Colour, Price, Weight, so its description is: (DefConcept Chairs(And OfficeFurniture(Atleast 1 Manufact) (Atmost 1 Manufact)..(All Weight Domain)))

Adding a new type consists of classifying a new concept description in the TBox. If we want to add an attribute to a product type, the operation consists of modifying the concept description and classifying the modified concept description.

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Figure 6.Adding the new type Chairs in the catalogue.

4.2.2.Adding a new category Adding a new category in the catalogue is more complex. There are many possible cases : ' The new category does not have sub-categories existing in the catalogue: for example we want to add the new categories SportsWear and SportingEquipement, without subcategories. So, their descriptions are: (DefPrimConcept SportsWear Catalog) (DefPrimConcept SportingEquipement Catalog)

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' The new category has sub-categories already existing in the catalogue. For example, the new category Sport has SportsWear and SportingEquipement as sub-categories. The new description to insert in the TBox is (DefPrimConcept Sports Catalog). The others will be update by (DefPrimConcept SportsWear Sport) and (DefPrimConcept SportingEquipement Sports). By re-classing all the concepts descriptions the inferred hierarchy is: ú &DWDORJ 6SRUWV

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The new category has existing types in the catalogue. Let suppose SweatShirt as being a type of SportsWear. We want to add new categories of SportsWear: Clothing and Shoes. We also want that SweatShirt to be a type of the new category Clothing. The new descriptions to insert are (DefPrimConcept Clothing SportsWear) and (DefPrimConcept Shoes SportsWear). The SweatShirt description is modified by (DefConcept SweatShirt (And Clothing … (All Size Domain))) The initial hierarchy with the type SweatShirt was: ú &DWDORJ 6SRUWV

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Figure 9.The hierarchy before adding new categories.

By classifying all the descriptions it becomes: ú &DWDORJ 6SRUWV 2IILFH(QYLURQPHQW

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Figure 10.Adding the categories Clothing and Shoes

4.3.Catalogue structure modification The operation of catalogue structure modification are category and type transfer by relating a sub-category (or type) from one category to another, from one or many catalogues. ' Category

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' Type transfer (one catalogue): this case is similar to the previous. The type description will be modified and automatically re-classified into the hierarchy.

' Category transfer between catalogues: in the E-Market Places, there is a global catalogue and sub-catalogues. The transfer operation consists of transferring a category from a catalogue to another. For example, the global catalogue HomeCat is composed by Catalog and CloyhingCat: HomeCat Catalog Office&Business Sports SportsWear Clothing SweatShirt(Material,Size,Colour) ClothingCat Coat Jacket

We want to transfer the SportsWear category from the catalogue Catalog to ClothingCat. This operation generates the transfer of all the sub-categories. The description of SportsWear will be replaced by (DefPrimConcept SportsWear ClothingCat) and by classifying it into the hierarchy, its sub-concepts will be automatically transferred, without updating their description. 4.4.Contextual cataloguing The contextual cataloguing is a dynamic classification of categories and sub-categories depending on the users characteristics or a context like the nationality. This dynamic classification will modify the catalogue the structure. Another case of dynamic classification is the global catalogue views depending on the provider (who wants for example to visualise its own catalogue), or the consumer characteristics (for example his age). This dynamic classification is generate when the system receive users (provider or consumer) information. If there is no particular information the catalogue will be visualised as initially defined. In the following we study the problem of classifications depending on the cultural environment of the consumer. For example, in most the classifications the type Telephone is a sub-category of ConsumerElectronics , whereas in German classification it is a subcategory of OfficeFurniture. A German user consulting the catalogue must see Telephone as sub-category of OfficeFurniture, whereas for another user it will be a sub-category of ConsumerElectronics. For modelling this case of cataloguing, Telephone is defined as sub-concept of ConsumerElectronics. We suppose that we have a context defined by a name and attributes: the concept User has the attributes Nationality and Age. A view GermanUser is defined as being all the User with Nationality=German. When an exception occurs, i.e. when the user is German, Telephone description is modified and updated by another one describing it as being a subconcept of OfficeFurniture. The classification mechanism detects the subsumption relationships between concepts and generates the hierarchy. This solution can be applied to other kinds of classification.

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We have seen in this section the principals cases of automatic cataloguing, and how the DLs can be used for these needs.

5.Conclusion One of the principal functionalities of the managing systems of E-Market Places is the automatic cataloguing of providers products or services. We have used the integration information system PICSEL [20] for implementing the different cases of cataloguing, from catalogue examples found on the Web. We have build the SNCF ontology (www.sncf.com), a travel French company, with the ALN-CARIN language. The ontology is composed by approximately 200 concepts and 60 roles. We have combined OntoClass with a component for the TBox management (add a new concept, modification of concept description…etc.) for the automatic cataloguing operations (Fig. 6). Another advantage of PICSEL is the OntoQuery component, which can be used for information retrieval and users query answering in the E6market Places. In this article we have identified the problems related to E-Commerce, and particularly the providers catalogue maintenance in E-Market Place. We have proposed the utilisation of the DLs for modelling the catalogues. We have showed that the automatic cataloguing can be realised using DLs. The others problems related to E-Commerce can be treated as follows: ' Catalogues dispersion on the Web: a unique application, like the E-Market Place, facilitates the use, the management ant the integration of the electronic catalogues. ' Many different formats: a unique format (Xml) can be used for efficient data treatment. ' Many categories classifications: using a global ontology describing a unique classification facilitates the catalogues integration, and allows fast product searching. To complete the cataloguing operations, another case to study the automatic integration of a new catalogue into the E-Market Place. Most of the existing catalogues are described with Xml. We can apply a structure inference algorithm [24], based on DLs, to generate a logical representation of an Xml new catalogue. It will be easily integrated into the global catalogue, always with the automatic classification service.

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