LIPIcs.ICDT.2025.28.pdf
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Generalized Covers for Conjunctive Queries
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Paraschos Koutris 
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28th International Conference on Database Theory (ICDT 2025)
Series: Leibniz International Proceedings in Informatics (LIPIcs)
Conference: International Conference on Database Theory (ICDT) - License:
Creative Commons Attribution 4.0 International license
- Publication Date: 2025-03-21
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Paraschos Koutris. Generalized Covers for Conjunctive Queries. In 28th International Conference on Database Theory (ICDT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 328, pp. 28:1-28:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)
https://doi.org/10.4230/LIPIcs.ICDT.2025.28
Abstract
Covers of query results were introduced as succinct lossless representations of join query outputs. A cover is a subset of the query result from which we can efficiently enumerate the output with constant delay and linear preprocessing time. However, covers are dependent on a single tree decomposition of the query. In this work, we generalize the notion of a cover to a set of multiple tree decompositions. We show that this generalization can potentially produce asymptotically smaller covers while maintaining the properties of constant-delay enumeration and linear preprocessing time. In particular, given a set of tree decompositions, we can determine exactly the asymptotic size of a minimum cover, which is tied to the notion of entropic width of the query. We also provide a simple greedy algorithm that computes this cover efficiently. Finally, we relate covers to semiring circuits when the semiring is idempotent.
Subject Classification
ACM Subject Classification
- Theory of computation → Database theory
Keywords
- Conjunctive Query
- tree decomposition
- cover
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