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Documents authored by Geck, Gaetano

Document
DOI: 10.4230/LIPIcs.ICDT.2022.8
Rewriting with Acyclic Queries: Mind Your Head

Authors: Gaetano Geck, Jens Keppeler, Thomas Schwentick, and Christopher Spinrath

Published in: LIPIcs, Volume 220, 25th International Conference on Database Theory (ICDT 2022)

Abstract
The paper studies the rewriting problem, that is, the decision problem whether, for a given conjunctive query Q and a set 𝒱 of views, there is a conjunctive query Q' over 𝒱 that is equivalent to Q, for cases where the query, the views, and/or the desired rewriting are acyclic or even more restricted. It shows that, if Q itself is acyclic, an acyclic rewriting exists if there is any rewriting. An analogous statement also holds for free-connex acyclic, hierarchical, and q-hierarchical queries. Regarding the complexity of the rewriting problem, the paper identifies a border between tractable and (presumably) intractable variants of the rewriting problem: for schemas of bounded arity, the acyclic rewriting problem is NP-hard, even if both Q and the views in 𝒱 are acyclic or hierarchical. However, it becomes tractable, if the views are free-connex acyclic (i.e., in a nutshell, their body is (i) acyclic and (ii) remains acyclic if their head is added as an additional atom).
Cite as

Gaetano Geck, Jens Keppeler, Thomas Schwentick, and Christopher Spinrath. Rewriting with Acyclic Queries: Mind Your Head. In 25th International Conference on Database Theory (ICDT 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 220, pp. 8:1-8:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{geck_et_al:LIPIcs.ICDT.2022.8,
  author =	{Geck, Gaetano and Keppeler, Jens and Schwentick, Thomas and Spinrath, Christopher},
  title =	{{Rewriting with Acyclic Queries: Mind Your Head}},
  booktitle =	{25th International Conference on Database Theory (ICDT 2022)},
  pages =	{8:1--8:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-223-5},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{220},
  editor =	{Olteanu, Dan and Vortmeier, Nils},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2022.8},
  URN =		{urn:nbn:de:0030-drops-158829},
  doi =		{10.4230/LIPIcs.ICDT.2022.8},
  annote =	{Keywords: rewriting, acyclic rewriting, acyclic conjunctive queries, free-connex queries, hierarchical queries, NP-hardness}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2020.13
Distribution Constraints: The Chase for Distributed Data

Authors: Gaetano Geck, Frank Neven, and Thomas Schwentick

Published in: LIPIcs, Volume 155, 23rd International Conference on Database Theory (ICDT 2020)

Abstract
This paper introduces a declarative framework to specify and reason about distributions of data over computing nodes in a distributed setting. More specifically, it proposes distribution constraints which are tuple and equality generating dependencies (tgds and egds) extended with node variables ranging over computing nodes. In particular, they can express co-partitioning constraints and constraints about range-based data distributions by using comparison atoms. The main technical contribution is the study of the implication problem of distribution constraints. While implication is undecidable in general, relevant fragments of so-called data-full constraints are exhibited for which the corresponding implication problems are complete for EXPTIME, PSPACE and NP. These results yield bounds on deciding parallel-correctness for conjunctive queries in the presence of distribution constraints.
Cite as

Gaetano Geck, Frank Neven, and Thomas Schwentick. Distribution Constraints: The Chase for Distributed Data. In 23rd International Conference on Database Theory (ICDT 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 155, pp. 13:1-13:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{geck_et_al:LIPIcs.ICDT.2020.13,
  author =	{Geck, Gaetano and Neven, Frank and Schwentick, Thomas},
  title =	{{Distribution Constraints: The Chase for Distributed Data}},
  booktitle =	{23rd International Conference on Database Theory (ICDT 2020)},
  pages =	{13:1--13:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-139-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{155},
  editor =	{Lutz, Carsten and Jung, Jean Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2020.13},
  URN =		{urn:nbn:de:0030-drops-119378},
  doi =		{10.4230/LIPIcs.ICDT.2020.13},
  annote =	{Keywords: tuple-generating dependencies, chase, conjunctive queries, distributed evaluation}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2016.9
Parallel-Correctness and Containment for Conjunctive Queries with Union and Negation

Authors: Gaetano Geck, Bas Ketsman, Frank Neven, and Thomas Schwentick

Published in: LIPIcs, Volume 48, 19th International Conference on Database Theory (ICDT 2016)

Abstract
Single-round multiway join algorithms first reshuffle data over many servers and then evaluate the query at hand in a parallel and communication-free way. A key question is whether a given distribution policy for the reshuffle is adequate for computing a given query, also referred to as parallel-correctness. This paper extends the study of the complexity of parallel-correctness and its constituents, parallel-soundness and parallel-completeness, to unions of conjunctive queries with and without negation. As a by-product it is shown that the containment problem for conjunctive queries with negation is coNEXPTIME-complete.
Cite as

Gaetano Geck, Bas Ketsman, Frank Neven, and Thomas Schwentick. Parallel-Correctness and Containment for Conjunctive Queries with Union and Negation. In 19th International Conference on Database Theory (ICDT 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 48, pp. 9:1-9:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{geck_et_al:LIPIcs.ICDT.2016.9,
  author =	{Geck, Gaetano and Ketsman, Bas and Neven, Frank and Schwentick, Thomas},
  title =	{{Parallel-Correctness and Containment for Conjunctive Queries with Union and Negation}},
  booktitle =	{19th International Conference on Database Theory (ICDT 2016)},
  pages =	{9:1--9:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-002-6},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{48},
  editor =	{Martens, Wim and Zeume, Thomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2016.9},
  URN =		{urn:nbn:de:0030-drops-57787},
  doi =		{10.4230/LIPIcs.ICDT.2016.9},
  annote =	{Keywords: Conjunctive queries, distributed evaluation}
}
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