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Complexity of Evaluating GQL Queries

Authors Diego Figueira , Anthony W. Lin , Liat Peterfreund

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Subject Classification

ACM Subject Classification
  • Theory of computation → Database theory
Keywords
  • Graph query languages
  • GQL
  • complexity
  • database theory

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Abstract

GQL has recently emerged as the standard query language over graph databases, particularly, property graphs. Indeed, this is analogous to the role of SQL for relational databases. Unlike SQL, however, fundamental problems regarding GQL are still unsolved, most notably the complexity of query evaluation. In this paper we provide a complete solution to this problem for the core fragment of GQL and for its extension with path restrictors. In particular, we show that the data complexity of these fragments is P^NP[log]-complete in general, and drops to NL-complete when restrictors are disallowed. Using techniques from embedded finite model theory, we show that this is true, even when the queries use data from infinite concrete domains such as real numbers with arithmetic. In proving these results, we establish and exploit tight connections between GQL and query languages over relational databases, especially extensions of relational calculus with transitive closure operators and fragments of second-order logic.

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Diego Figueira, Anthony W. Lin, and Liat Peterfreund. Complexity of Evaluating GQL Queries. In 29th International Conference on Database Theory (ICDT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 365, pp. 13:1-13:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026) https://doi.org/10.4230/LIPIcs.ICDT.2026.13

Author Details

Diego Figueira
  • University of Bordeaux, CNRS, Bordeaux INP, LaBRI, UMR 5800, F-33400, Talence, France
Anthony W. Lin
  • University of Kaiserslautern-Landau, Germany
  • MPI-SWS, Kaiserslautern, Germany
Liat Peterfreund
  • Hebrew University of Jerusalem, Israel

Funding

  • Figueira, Diego: Partially supported by ANR grants INTENDED (ANR-19-CHIA-0014) and EXPAND (ANR-25-CE23-1215).
  • Lin, Anthony W.: Supported by the European Research Council under Grant No. 101089343 (LASD).
  • Peterfreund, Liat: Supported by Israel Science Foundation 2355/24.

Acknowledgements

We thank Michael Benedikt, Leonid Libkin and anonymous reviewers for valuable feedback.

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