Semantic based query rewriting in heterogeneous sources

New challenges are raised with the large increase in the number of Web accessible data sources such as (a) identification of data sources that are relevant to the user query and (b) fulfilling the requirements of user´s queries. Commonly used integration systems are facing problems because (i) sources are semantically heterogeneous and are autonomous; (ii) their schemas and database design are different and (iii) their query languages are also different. In this paper we highlight some issues of semantic-based query rewriting and propose a solution to (a) provide uniform access to all sources and (b) relieve users to understand local schemas.