Resolving Fragmentation Conflicts in Schema Integration

Research on schema integration leads to the identification of many different conflict types. Some of them received much attention and many papers proposed solutions for their resolution. However, literature usually focuses on traditional problems, whilst new kinds of schema discrepancies, due to the object orientation or the generalization concept, are not really treated. Moreover, most of the proposed methodologies and strategies only allow binary comparisons between items to be integrated. This paper discusses n-ary (also called one-many) conflicts, and particularly the three fragmentation conflict types. These conflict types need specific operators for schema comparison. We propose a simple unified language for easy specification of these conflicts, and give many different techniques to solve them. We emphasize the benefit of separating the declaration of the correspondences from the choice of resolution technique. Our discourse is illustrated with the entity-relationship model, but our solutions can be applied in any data model. We propose several conflict resolution techniques that can be applied on a concept which has the generalization (the entity type) and different techniques that must be applied on a concept which has not (the relationship type).