License: Creative Commons Attribution 4.0 International license (CC BY 4.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.ICDT.2023.24
URN: urn:nbn:de:0030-drops-177663
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Figueira, Diego ; Padmanabha, Anantha ; Segoufin, Luc ; Sirangelo, Cristina

A Simple Algorithm for Consistent Query Answering Under Primary Keys

LIPIcs-ICDT-2023-24.pdf (2 MB)


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.

BibTeX - Entry

  author =	{Figueira, Diego and Padmanabha, Anantha and Segoufin, Luc and Sirangelo, Cristina},
  title =	{{A Simple Algorithm for Consistent Query Answering Under Primary Keys}},
  booktitle =	{26th International Conference on Database Theory (ICDT 2023)},
  pages =	{24:1--24:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-270-9},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{255},
  editor =	{Geerts, Floris and Vandevoort, Brecht},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{},
  URN =		{urn:nbn:de:0030-drops-177663},
  doi =		{10.4230/LIPIcs.ICDT.2023.24},
  annote =	{Keywords: consistent query answering, primary keys, conjunctive queries}

Keywords: consistent query answering, primary keys, conjunctive queries
Collection: 26th International Conference on Database Theory (ICDT 2023)
Issue Date: 2023
Date of publication: 17.03.2023

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