Query optimization by attributes annotation in a database mediation system

The large amount of information available on autonomous, distributed and heterogeneous data sources requires a scheme of retrieval, selection and analysis, increasingly powerful to locate and extract precisely the desired information. The information integration systems offer an access to multiple data sources through queries on a global schema. A query posed on a database mediation system will be divided and sent to all the databases containing the attributes appearing in the query. But obviously, there are some databases which do not contain any answer. In this paper we propose to annotate numerical and enumerated attributes and to save these annotations in the mediator. By using these annotations, a query on the mediator will be sent only to the databases that surely contain answers.