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Output-Sensitive Evaluation of Acyclic Conjunctive Regular Path Queries

Authors Mahmoud Abo Khamis , Alexandru-Mihai Hurjui , Ahmet Kara , Dan Olteanu , Dan Suciu , Zilu Tian

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LIPIcs.ICDT.2026.18.pdf
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Subject Classification

ACM Subject Classification
  • Information systems → Graph-based database models
  • Theory of computation → Database query processing and optimization (theory)
  • Theory of computation → Graph algorithms analysis
Keywords
  • graph databases
  • regular path queries
  • output-sensitive algorithms

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Abstract

Conjunctive Regular Path Queries, or CRPQs for short, are an essential construct in graph query languages. In this paper, we propose the first output-sensitive algorithm for evaluating acyclic CRPQs. It is output-sensitive in the sense that its complexity is a function of the sizes of the input graph and of the query output and not of the output sizes of the regular expressions that appear in the query, as these latter sizes can be larger than the query output size.
Our algorithm proceeds in two stages. In the first stage, it contracts the given query into a free-connex acyclic one such that the output of the original query can be obtained from the output of the contracted one. This contraction removes bound variables by composing regular expressions or by promoting bound variables to free ones. The minimum necessary number of promoted bound variables gives the contraction width, which is a novel parameter specific to CRPQs. In the second stage, our algorithm evaluates the free-connex acyclic CRPQ and projects away the columns of the promoted bound variables. It ensures output-sensitivity by computing the calibrated outputs of the regular expressions appearing in the free-connex acyclic CRPQ in time proportional to their sizes.
Our algorithm has lower complexity than the state-of-the-art approaches for problem instances where the query output is asymptotically smaller than the output sizes of the regular expressions that appear in the query.

Cite As Get BibTex

Mahmoud Abo Khamis, Alexandru-Mihai Hurjui, Ahmet Kara, Dan Olteanu, Dan Suciu, and Zilu Tian. Output-Sensitive Evaluation of Acyclic Conjunctive Regular Path Queries. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 18:1-18:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026) https://doi.org/10.4230/LIPIcs.ICDT.2026.18

Author Details

Mahmoud Abo Khamis
  • RelationalAI, Berkeley, CA, USA
Alexandru-Mihai Hurjui
  • University of Zurich, Switzerland
Ahmet Kara
  • OTH Regensburg, Germany
Dan Olteanu
  • University of Zurich, Switzerland
Dan Suciu
  • University of Washington, Seattle, WA, USA
Zilu Tian
  • University of Zurich, Switzerland

Funding

This work was partially supported by NSF-BSF 2109922, NSF-IIS 2314527, NSF-SHF 2312195, and SNSF 200021-231956.

References

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