We consider here scalar aggregation queries in databases that may violate a given set of functional dependencies. We 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. We show how to compute such answers. We provide a complete characterization of the computational complexity of this problem. We 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.

Theoretical Computer Science
School of Computer Science

Arenas, M. (Marcelo), Bertossi, L, Chomicki, J. (Jan), He, X. (Xin), Raghavan, V. (Vijay), & Spinrad, J. (Jeremy). (2003). Scalar aggregation in inconsistent databases. In Theoretical Computer Science (Vol. 296, pp. 405–434). doi:10.1016/S0304-3975(02)00737-5