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In this paper, we study consistent query answering in tables with nulls andfunctional dependencies. Given such a table T, we consider the set Tuples ofall tuples that can be built up from constants appearing in T, and we use settheoretic semantics for tuples and functional dependencies to characterize thetuples of Tuples in two orthogonal ways: first as true or false tuples, andthen as consistent or inconsistent tuples. Queries are issued against T andevaluated in Tuples. In this setting, we consider a query Q: select X from Twhere Condition over T and define its consistent answer to be the set of tuplesx in Tuples such that: x is a true and consistent tuple with schema X and thereexists a true super-tuple t of x in Tuples satisfying the condition. We showthat, depending on the status that the super-tuple t has in Tuples, there aredifferent types of consistent answer to Q. The main contributions of the paperare: (a) a novel approach to consistent query answering not using tablerepairs; (b) polynomial algorithms for computing the sets of true-false tuplesand the sets of consistent-inconsistent tuples of Tuples; (c) polynomialalgorithms in the size of T for computing different types of consistent answerfor both conjunctive and disjunctive queries; and (d) a detailed discussion ofthe differences between our approach and the approaches using table repairs.

Consistent Query Answering without Repairs in Tables with Nulls and Functional Dependencies