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European Journal of Scientific Research ISSN 1450-216X Vol.20 No.2 (2008), pp.374-383 © EuroJournals Publishing, Inc. 2008 http://www.eurojournals.com/ejsr.htm Generic Architecture Based Agent for Context and Schema Mediation Benharzallah Saber Department of Computer science University of Mohamed Khider Biskra, 07000Algery E-mail: sbharz@yahoo.fr Kazar Okba Department of Computer science University of Mohamed Khider Biskra, 07000Algery E-mail: Kazarokba@yahoo.fr Abstract This paper is to propose a generic architecture based agent for the semantic mediation of the information systems. This solution combines two approaches (schema mediation and context mediation) in a progressive way and uses new technologies in order to ensure better advantages of the two approaches. Our solution makes it possible to solve the majority of the semantic conflicts in a dynamic way and respects the properties of interoperability (autonomy, scalability, evolutionarily...) by using the concept of intelligent agent 1. Introduction The evolutions of these last years, as well in terms of organization as of technology, generated the multiplication and the dissemination of heterogeneous information, thus returning the information systems heterogeneous and distributed. The cooperation of systems is confronted with many problems of heterogeneities and must take account of the open and dynamic aspect of modern environments. Various types of heterogeneity can be met. Technical heterogeneity refers to the coexistence of disparate material platform and operating systems. Syntactic heterogeneity relates to the diversity of choice on the level of the models and the data types. Structural heterogeneity characterizes the differences between the concepts of the data models (schematic conflicts) and between query languages. Semantic heterogeneity refers to cases of different interpretation. Several types of semantic conflicts appear: naming conflicts (taxonomic problems and linguistics), values conflicts (units and scales problems...) The solutions for the interoperability of the information systems evolved to the semantic mediation of the systems, defined [5] [7], "any process of database interoperability allowing to solve the semantic conflicts related to the objects values domain and dependent on the objects structuring of the real world" We propose a solution for the semantic mediation of the information systems, section 2 presents a synthesis of the various existing approaches and then introduced the key points of our solution. Two sections 3.3 and 3.4 describe the architecture of the mediation and the various types of agents. Then sections 3.5, 3.6 and 3.7 explain the protocol which makes it possible to add systems, the
Generic Architecture Based Agent for Context and Schema Mediation 375 mediation model and the queries processing. Finally, sections 3.8, 3.9 and 3.10 describe the communication language between agents, a cooperation scenario and the prototype implementation. 2. Interoperability approaches of the information systems We compare the various approaches according to the following criteria: 1. The formulation of the user query (in ontology/schema terms) 2. Capacity of the system to solve the majority of the semantic conflicts (solved conflicts type). 3. The degree of automation of the resolution process. 4. The resolution of the requests (treated statically/dynamically) 5. Transparency, evolutionarily (add/remove/modification of an information sources) and the scalability (capacity to manage an exponential increase in information sources) of architecture. Many solutions were proposed to solve the interoperability problem of information systems (virtual integration) [3] [4] [2], The most recent systems are the broking information systems whose objective is oriented directed on the semantic conflicts resolution (or semantic mediation). Three approaches [6] [8] [2] are distinguished: The schema mediation is a direct extension of the federate approach. Data conflicts solved statically. It consists with associates to the mediator a knowledge set (mapping rules) allowing locating the data sources. An execution plan is established by rules, which define where are the relevant data to a query processing are. The Global schema is generally specified by interfaces object, logic or XML. In this approach the transparency is assured, the degree of automation resolution is weak and the scalability and the evolutionarily are respected compared to the context mediation. The majority of the solutions not solve the semantic conflicts of values [02]. A first tendency can be illustrated using work of Kashyap and Seth carried in 1994 for the context mediation approach. Sensitive to the semantic heterogeneity problem which can make difficult query processing, they introduced the concept of context. The role of the mediator in this approach, it identifies and locates, transforms and integrates the relevant data according to semantics associated with a query [02]. The data conflicts resolution is dynamic and does not require the definition of a mediation schema. The user's queries are generally formulated in terms of ontologies. The data are integrated dynamically according to the semantic information contained in the description of the contexts. This approach allows the best taken into account of the evolution of the local sources and thus the automation degree is better compared to the schema mediation. Two categories of context mediation are defined: the approach single domain SIMS [9], COIN [10] works on a single domain where all the contexts are defined by using a universal of consensual speech. The scalability and evolutionarily are respected but remains limited by the unicity of the domain; and multi domains approaches Infosleuth [11], Observer [12]. In this approach the conflicts resolution is a dynamic way, during the execution of the queries allows the best taken into account of the evolution of the local sources and thus the automation degree is better compared to the schema mediation. Concerning the semantic conflicts, the majority of the projects solve only the taxonomic conflicts Coin [10]. The resolution of the values conflicts either is guided by the user Infosleuth [11], or unsolved in the majority of the cases Observer [12] [13]. The hybrid approach combines between the schema mediation and the context mediation, named DILEMMA [02][24] and based on the queries static resolution. The mediation is ensured by a couple mediator/wrapper and a knowledge base associated with each system taking part in the cooperation. The mediator comprises a queries processor and a facilitator. This last is composed of two services: a fusion service (distant context, local context) and a generation service of mediation rules. Shared information is described in a data model directed objects deductive and attached to an applicability or local semantic context expressed using terminological logic. This approach offers a better transparency like the schema mediation and makes it possible to solve the values semantic conflicts, but in a manner a priori. The automation degree is better compared to the schema mediation
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