Obtaining More Answers from Information Integration Systems

The current generation of rewriting-algorithms in source-centric (local-as-view) information integration systems all produce a reformulated query that retrieves what has been thought of as ”the best obtainable” answer, given the circumstances that the source-centric approach introduces incomplete information into the virtual global relations. This ”best obtainable” answer does not however allow partial information. We define the semantics of partial facts, and provide two methods for computing partial answers. The first method is tableau-based and is a generalization of the ”inverse-rules” approach. The second method is a generalization of the rewriting approach, and is based on partial containment mappings introduced in the paper.