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Abstract

We propose an extension of a mediator architecture. This extension is oriented to ontology-driven data integration. In our architecture ontologies are not managed by an extemal component or service, but are integrated in the mediation layer. This approach implies rethinking the mediator design, but at the same time provides advantages from a database perspective. Some of these advantages include the application of optimization and evaluation techniques that use and combine information from all abstraction levels (physical schema, logical schema and semantic information defined by ontology). 1. Introduction Although the Web is probably the richest information repository in human history, users cannot specify what they want from it. Two major problems that arise in current search engines (Heflin, 2001) are: a) polysemy, when the same word is used with different meanings; b) synonymy, when two different words have the same meaning. Polysemy causes irrelevant information retrieval. On the other hand, synonymy produces lost of useful documents. The lack of a capability to understand the context of the words and the relationships among required terms, explains many of the lost and false results produced by search engines. The Semantic Web will bring structure to the meaningful content of Web pages, giving semantic relationships among terms and possibly avoiding the previous problems. Various proposals have appeared for meta-data representation and communication standards, and other services and tools that may eventually merge into the global Semantic Web (Berners-lee, 2001). Hopefully, in the next few years we will see the universal adoption of open standards for representation and sharing of meta-information. In this environment, software agents roaming from page to page can readily carry out sophisticated tasks for users (Berners-Lee, 2001). In this context, ontologies can be seen as metadata that represent semantic of data; providing a knowledge domain standard vocabulary, like DTDs and XML Schema do. If its pages were so structured, the Web could be seen as a heterogeneous collection of autonomous databases. This suggests that techniques developed in the Database area could be useful. Database research mainly deals with efficient storage and retrieval and with powerful query languages.