2026-07-25T12:07:38Z https://drops.dagstuhl.de/oai

oai:drops-oai.dagstuhl.de:17766 2024-03-06T11:00:26Z ddc:004 open_access

A Simple Algorithm for Consistent Query Answering Under Primary Keys Figueira, Diego Padmanabha, Anantha Segoufin, Luc Sirangelo, Cristina consistent query answering primary keys conjunctive queries We consider the dichotomy conjecture for consistent query answering under primary key constraints. It states that, for every fixed Boolean conjunctive query q, testing whether q is certain (i.e. whether it evaluates to true over all repairs of a given inconsistent database) is either polynomial time or coNP-complete. This conjecture has been verified for self-join-free and path queries. We propose a simple inflationary fixpoint algorithm for consistent query answering which, for a given database, naively computes a set Δ of subsets of database repairs with at most k facts, where k is the size of the query q. The algorithm runs in polynomial time and can be formally defined as: 1) Initialize Δ with all sets S of at most k facts such that S⊧ q. 2) Add any set S of at most k facts to Δ if there exists a block B (i.e., a maximal set of facts sharing the same key) such that for every fact a ∈ B there is a set S' ∈ Δ contained in S ∪ {a}. The algorithm answers "q is certain" iff Δ eventually contains the empty set. The algorithm correctly computes certainty when the query q falls in the polynomial time cases of the known dichotomies for self-join-free queries and path queries. For arbitrary Boolean conjunctive queries, the algorithm is an under-approximation: the query is guaranteed to be certain if the algorithm claims so. However, there are polynomial time certain queries (with self-joins) which are not identified as such by the algorithm. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Diego Figueira and Anantha Padmanabha and Luc Segoufin and Cristina Sirangelo 2023 Is Part Of LIPIcs, Volume 255, 26th International Conference on Database Theory (ICDT 2023) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.ICDT.2023.24 urn:nbn:de:0030-drops-177663 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2023.24 eng https://creativecommons.org/licenses/by/4.0/legalcode