Query processing plays a fundamental role in current information systems that need to access independent and heterogeneous databases. This paper presents a new approach to querying heterogeneous databases that maps the semantics of query objects onto database schemas. The sematics is captured by the definitions of classes in an ontology, and a similarity function identifies not only equivalent but also semantically similar classes associated with a user's request. These similar classes are then

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... mapped onto a database schema, which is compared with schemas of heterogeneous databases to obtain entities in the databases that answer the query.