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DOI: 10.4230/LIPIcs.ICDT.2019.23
URL: http://drops.dagstuhl.de/opus/volltexte/2019/10325/
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Koutris, Paraschos ; Wijsen, Jef

Consistent Query Answering for Primary Keys in Logspace

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LIPIcs-ICDT-2019-23.pdf (0.6 MB)


Abstract

We study the complexity of consistent query answering on databases that may violate primary key constraints. A repair of such a database is any consistent database that can be obtained by deleting a minimal set of tuples. For every Boolean query q, CERTAINTY(q) is the problem that takes a database as input and asks whether q evaluates to true on every repair. In [Koutris and Wijsen, ACM TODS, 2017], the authors show that for every self-join-free Boolean conjunctive query q, the problem CERTAINTY(q) is either in P or coNP-complete, and it is decidable which of the two cases applies. In this paper, we sharpen this result by showing that for every self-join-free Boolean conjunctive query q, the problem CERTAINTY(q) is either expressible in symmetric stratified Datalog (with some aggregation operator) or coNP-complete. Since symmetric stratified Datalog is in L, we thus obtain a complexity-theoretic dichotomy between L and coNP-complete. Another new finding of practical importance is that CERTAINTY(q) is on the logspace side of the dichotomy for queries q where all join conditions express foreign-to-primary key matches, which is undoubtedly the most common type of join condition.

BibTeX - Entry

@InProceedings{koutris_et_al:LIPIcs:2019:10325,
  author =	{Paraschos Koutris and Jef Wijsen},
  title =	{{Consistent Query Answering for Primary Keys in Logspace}},
  booktitle =	{22nd International Conference on Database Theory (ICDT 2019)},
  pages =	{23:1--23:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-101-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{127},
  editor =	{Pablo Barcelo and Marco Calautti},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{http://drops.dagstuhl.de/opus/volltexte/2019/10325},
  doi =		{10.4230/LIPIcs.ICDT.2019.23},
  annote =	{Keywords: conjunctive queries, consistent query answering, Datalog, primary keys}
}

Keywords: conjunctive queries, consistent query answering, Datalog, primary keys
Seminar: 22nd International Conference on Database Theory (ICDT 2019)
Issue Date: 2019
Date of publication: 19.03.2019


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