Direction du Patrimoine de I'edition 395, rue Wellington Ottawa ON K1A 0N4 Canada Bien que ces formulaires aient inclus dans la pagination, il n'y aura aucun contenu manquant. i * i Canada Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Abstract For several reasons a database may not satisfy certain integrity constraints (ICs), for example, when it is the result of integrating several independent data sources. However, most likely,

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... on in it is still consistent with the ICs; and could be retrieved when queries are answered. Consistent answers with respect to a set of ICs have been characterized as answers th at can be obtained from every possible minimal repair of the database. The goal of this research is to develop methods to retrieve consistent answers for a wide and practical class of constraints and queries from relational databases and from data integration systems. We will put special interest on databases with null values. We will give a semantics of satisfaction of constraints in the presence of null th at generalizes the one used in commercial DBMS. Since there are interesting connections between the area of consistently querying virtual d ata integration systems and other areas, like querying incomplete databases, merging inconsistent theories, semantic reconciliation of data, schema mapping, data exchange, and query answering in peer data management systems, the results of this research could also be applied to them. In our research, we explore in more depth the connection with virtual d ata integration systems and peer data management systems. ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. To m y husband Leo Ferres In m emory of Javier Pinto iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.