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A Purely Regular Approach to Non-Regular Core Spanners

Authors Markus L. Schmid , Nicole Schweikardt

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Author Details

Markus L. Schmid
  • Humboldt-Universität zu Berlin, Germany
Nicole Schweikardt
  • Humboldt-Universität zu Berlin, Germany

Funding

  • Schmid, Markus L.: Supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) - project number 416776735 (gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 416776735).
  • Schweikardt, Nicole: Partially supported by the ANR project EQUUS ANR-19-CE48-0019; funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project number 431183758 (gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 431183758).

Acknowledgements

We wish to thank the anonymous reviewers for their valuable feedback that improved the readability of this paper.

Cite AsGet BibTex

Markus L. Schmid and Nicole Schweikardt. A Purely Regular Approach to Non-Regular Core Spanners. In 24th International Conference on Database Theory (ICDT 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 186, pp. 4:1-4:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
https://doi.org/10.4230/LIPIcs.ICDT.2021.4

Abstract

The regular spanners (characterised by vset-automata) are closed under the algebraic operations of union, join and projection, and have desirable algorithmic properties. The core spanners (introduced by Fagin, Kimelfeld, Reiss, and Vansummeren (PODS 2013, JACM 2015) as a formalisation of the core functionality of the query language AQL used in IBM’s SystemT) additionally need string equality selections and it has been shown by Freydenberger and Holldack (ICDT 2016, Theory of Computing Systems 2018) that this leads to high complexity and even undecidability of the typical problems in static analysis and query evaluation. We propose an alternative approach to core spanners: by incorporating the string-equality selections directly into the regular language that represents the underlying regular spanner (instead of treating it as an algebraic operation on the table extracted by the regular spanner), we obtain a fragment of core spanners that, while having slightly weaker expressive power than the full class of core spanners, arguably still covers the intuitive applications of string equality selections for information extraction and has much better upper complexity bounds of the typical problems in static analysis and query evaluation.

Subject Classification

ACM Subject Classification
  • Information systems → Information retrieval
  • Theory of computation → Automata extensions
  • Theory of computation → Regular languages
  • Theory of computation → Design and analysis of algorithms
  • Theory of computation → Database query languages (principles)
Keywords
  • Document spanners
  • regular expressions with backreferences

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References

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