On First-Order Query Rewriting for Incomplete Database Histories

Abstract

Multiwords are defined as words in which single symbols can be replaced by nonempty sets of symbols. Such a set of symbols captures uncertainty about the exact symbol. Words are obtained from multiwords by selecting a single symbol from every set. A pattern is certain in a multiword W if it occurs in every word that can be obtained from W. For a given pattern, we are interested in finding a logic formula that recognizes the multiwords in which that pattern is certain. This problem can be seen as a special case of consistent query answering (CQA).We show how our results can be applied in CQA on database histories under primary key constraints.