Approximation Algorithms for Computing Certain Answers over Incomplete Databases

Certain answers are a widely accepted semantics of query answering over incomplete databases. Since their computation is a coNP-hard problem, recent research has focused on developing evaluation algorithms with correctness guarantees, that is, techniques computing a sound but possibly incomplete set of certain answers. In this paper, we show how novel evaluation algorithms with correctness guarantees can be developed leveraging conditional tables and the conditional evaluation of queries, while retaining polynomial time data complexity.

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