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DOI: 10.4230/LIPIcs.ICDT.2025.23

A Simple Algorithm for Worst Case Optimal Join and Sampling

Authors: Florent Capelli, Oliver Irwin, and Sylvain Salvati

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

Abstract

We present an elementary branch and bound algorithm with a simple analysis of why it achieves worstcase optimality for join queries on classes of databases defined respectively by cardinality or acyclic degree constraints. We then show that if one is given a reasonable way for recursively estimating upper bounds on the number of answers of the join queries, our algorithm can be turned into algorithm for uniformly sampling answers with expected running time Õ(UP/OUT) where UP is the upper bound, OUT is the actual number of answers and Õ(⋅) ignores polylogarithmic factors. Our approach recovers recent results on worstcase optimal join algorithm and sampling in a modular, clean and elementary way.

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Florent Capelli, Oliver Irwin, and Sylvain Salvati. A Simple Algorithm for Worst Case Optimal Join and Sampling. In 28th International Conference on Database Theory (ICDT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 328, pp. 23:1-23:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{capelli_et_al:LIPIcs.ICDT.2025.23,
  author =	{Capelli, Florent and Irwin, Oliver and Salvati, Sylvain},
  title =	{{A Simple Algorithm for Worst Case Optimal Join and Sampling}},
  booktitle =	{28th International Conference on Database Theory (ICDT 2025)},
  pages =	{23:1--23:19},
  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.2025.23},
  URN =		{urn:nbn:de:0030-drops-229647},
  doi =		{10.4230/LIPIcs.ICDT.2025.23},
  annote =	{Keywords: join queries, worst-case optimality, uniform sampling}
}

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DOI: 10.4230/LIPIcs.ICDT.2024.13

Direct Access for Conjunctive Queries with Negations

Authors: Florent Capelli and Oliver Irwin

Published in: LIPIcs, Volume 290, 27th International Conference on Database Theory (ICDT 2024)

Abstract

Given a conjunctive query Q and a database 𝐃, a direct access to the answers of Q over 𝐃 is the operation of returning, given an index j, the j-th answer for some order on its answers. While this problem is #P-hard in general with respect to combined complexity, many conjunctive queries have an underlying structure that allows for a direct access to their answers for some lexicographical ordering that takes polylogarithmic time in the size of the database after a polynomial time precomputation. Previous work has precisely characterised the tractable classes and given fine-grained lower bounds on the precomputation time needed depending on the structure of the query. In this paper, we generalise these tractability results to the case of signed conjunctive queries, that is, conjunctive queries that may contain negative atoms. Our technique is based on a class of circuits that can represent relational data. We first show that this class supports tractable direct access after a polynomial time preprocessing. We then give bounds on the size of the circuit needed to represent the answer set of signed conjunctive queries depending on their structure. Both results combined together allow us to prove the tractability of direct access for a large class of conjunctive queries. On the one hand, we recover the known tractable classes from the literature in the case of positive conjunctive queries. On the other hand, we generalise and unify known tractability results about negative conjunctive queries - that is, queries having only negated atoms. In particular, we show that the class of β-acyclic negative conjunctive queries and the class of bounded nest set width negative conjunctive queries admit tractable direct access.

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Florent Capelli and Oliver Irwin. Direct Access for Conjunctive Queries with Negations. In 27th International Conference on Database Theory (ICDT 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 290, pp. 13:1-13:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{capelli_et_al:LIPIcs.ICDT.2024.13,
  author =	{Capelli, Florent and Irwin, Oliver},
  title =	{{Direct Access for Conjunctive Queries with Negations}},
  booktitle =	{27th International Conference on Database Theory (ICDT 2024)},
  pages =	{13:1--13:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-312-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{290},
  editor =	{Cormode, Graham and Shekelyan, Michael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2024.13},
  URN =		{urn:nbn:de:0030-drops-197958},
  doi =		{10.4230/LIPIcs.ICDT.2024.13},
  annote =	{Keywords: Conjunctive queries, factorized databases, direct access, hypertree decomposition}
}

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A Simple Algorithm for Worst Case Optimal Join and Sampling

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Direct Access for Conjunctive Queries with Negations

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