On condensing database repairs obtained by tuple deletions

An inconsistent database is repaired by restricting it to a maximal consistent subset of its tuples. Typically, this gives rise to a multitude of possible repairs, and hence to a multitude of possible answers to a given query. The consistent (or certain) query answer consists of the tuples that are in all possible answers. For conjunctive queries, this consistent answer can also be obtained by asking the query once on a database that is maximal homomorphic to all repairs. We study the complexity of constructing this maximal homomorphic database for different classes of constraints and queries.