Scalar Aggregation in Inconsistent Databases

The authors consider here scalar aggregation queries in databases that may violate a given set of functional dependencies. The authors define consistent answers to such queries to be greatest lowest/least upper bounds on the value of the scalar function across all (minimal) repairs of the database. They show how to compute such answers. They provide a complete characterization of the computational complexity of this problem. The authors also show how tractability can be improved in several special cases (one involves a novel application of Boyce-Codd Normal Form) and present a practical hybrid query evaluation method.