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Invited Talk

DOI: 10.4230/LIPIcs.ICDT.2026.1

Query Decompositions and All That (Invited Talk)

Authors: Kyle Deeds, Timo Camillo Merkl, Reinhard Pichler, and Dan Suciu

Published in: LIPIcs, Volume 365, 29th International Conference on Database Theory (ICDT 2026)

Abstract

The close relationship between Conjunctive Queries (CQs) and Constraint Satisfaction Problems (CSPs) has long been known. Nevertheless, apart from decomposition methods, research on efficient query evaluation or constraint solving algorithms has developed rather independently. In this article, we illustrate how search algorithms originating from the CSP community can be fruitfully applied to query evaluation - either by further developing the original search algorithms or by combining them with query decomposition methods. It turns out that the resulting approaches may indeed lead to lower time and/or space complexity than previous query evaluation methods.

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Kyle Deeds, Timo Camillo Merkl, Reinhard Pichler, and Dan Suciu. Query Decompositions and All That (Invited Talk). In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 1:1-1:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{deeds_et_al:LIPIcs.ICDT.2026.1,
  author =	{Deeds, Kyle and Merkl, Timo Camillo and Pichler, Reinhard and Suciu, Dan},
  title =	{{Query Decompositions and All That}},
  booktitle =	{29th International Conference on Database Theory (ICDT 2026)},
  pages =	{1:1--1:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-413-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{365},
  editor =	{ten Cate, Balder and Funk, Maurice},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2026.1},
  URN =		{urn:nbn:de:0030-drops-256158},
  doi =		{10.4230/LIPIcs.ICDT.2026.1},
  annote =	{Keywords: Query evaluation, Query decompositions, Complexity}
}

Document

DOI: 10.4230/LIPIcs.ICDT.2025.17

Partition Constraints for Conjunctive Queries: Bounds and Worst-Case Optimal Joins

Authors: Kyle Deeds and Timo Camillo Merkl

Published in: LIPIcs, Volume 328, 28th International Conference on Database Theory (ICDT 2025)

Abstract

In the last decade, various works have used statistics on relations to improve both the theory and practice of conjunctive query execution. Starting with the AGM bound which took advantage of relation sizes, later works incorporated statistics like functional dependencies and degree constraints. Each new statistic prompted work along two lines; bounding the size of conjunctive query outputs and worst-case optimal join algorithms. In this work, we continue in this vein by introducing a new statistic called a partition constraint. This statistic captures latent structure within relations by partitioning them into sub-relations which each have much tighter degree constraints. We show that this approach can both refine existing cardinality bounds and improve existing worst-case optimal join algorithms.

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Kyle Deeds and Timo Camillo Merkl. Partition Constraints for Conjunctive Queries: Bounds and Worst-Case Optimal Joins. In 28th International Conference on Database Theory (ICDT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 328, pp. 17:1-17:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{deeds_et_al:LIPIcs.ICDT.2025.17,
  author =	{Deeds, Kyle and Merkl, Timo Camillo},
  title =	{{Partition Constraints for Conjunctive Queries: Bounds and Worst-Case Optimal Joins}},
  booktitle =	{28th International Conference on Database Theory (ICDT 2025)},
  pages =	{17:1--17:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-364-5},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{328},
  editor =	{Roy, Sudeepa and Kara, Ahmet},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2025.17},
  URN =		{urn:nbn:de:0030-drops-229588},
  doi =		{10.4230/LIPIcs.ICDT.2025.17},
  annote =	{Keywords: Worst-Case Optimal Joins, Cardinality Bounds, Degeneracy, Degree Constraints, Partition Constraints}
}

Document

DOI: 10.4230/LIPIcs.ICDT.2023.10

Diversity of Answers to Conjunctive Queries

Authors: Timo Camillo Merkl, Reinhard Pichler, and Sebastian Skritek

Published in: LIPIcs, Volume 255, 26th International Conference on Database Theory (ICDT 2023)

Abstract

Enumeration problems aim at outputting, without repetition, the set of solutions to a given problem instance. However, outputting the entire solution set may be prohibitively expensive if it is too big. In this case, outputting a small, sufficiently diverse subset of the solutions would be preferable. This leads to the Diverse-version of the original enumeration problem, where the goal is to achieve a certain level d of diversity by selecting k solutions. In this paper, we look at the Diverse-version of the query answering problem for Conjunctive Queries and extensions thereof. That is, we study the problem if it is possible to achieve a certain level d of diversity by selecting k answers to the given query and, in the positive case, to actually compute such k answers.

Cite as

Timo Camillo Merkl, Reinhard Pichler, and Sebastian Skritek. Diversity of Answers to Conjunctive Queries. In 26th International Conference on Database Theory (ICDT 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 255, pp. 10:1-10:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{merkl_et_al:LIPIcs.ICDT.2023.10,
  author =	{Merkl, Timo Camillo and Pichler, Reinhard and Skritek, Sebastian},
  title =	{{Diversity of Answers to Conjunctive Queries}},
  booktitle =	{26th International Conference on Database Theory (ICDT 2023)},
  pages =	{10:1--10:19},
  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 =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2023.10},
  URN =		{urn:nbn:de:0030-drops-177529},
  doi =		{10.4230/LIPIcs.ICDT.2023.10},
  annote =	{Keywords: Query Answering, Diversity of Solutions, Complexity, Algorithms}
}

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Documents authored by Merkl, Timo Camillo

Query Decompositions and All That (Invited Talk)

Abstract

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Partition Constraints for Conjunctive Queries: Bounds and Worst-Case Optimal Joins

Abstract

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Diversity of Answers to Conjunctive Queries

Abstract

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