On the Role of Integrity Constraints in Data Integration

We discuss the issue of dealing with integrity constraints over the global schema in data integration. On the one hand, integrity constraints can be used to extract more information from incomplete sources, similarly to the case of databases with incomplete information. On the other hand, integrity constraints raise the problem of dealing with the inconsistency of the whole system, due to contradictory data at the sources. We also present a data integration system developed by taking into account such issues.