N-ary Queries by Tree Automata

Authors Joachim Niehren, Laurent Planque, Jean-Marc Talbot, Sophie Tison

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Joachim Niehren
Laurent Planque
Jean-Marc Talbot
Sophie Tison

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Joachim Niehren, Laurent Planque, Jean-Marc Talbot, and Sophie Tison. N-ary Queries by Tree Automata. In Foundations of Semistructured Data. Dagstuhl Seminar Proceedings, Volume 5061, pp. 1-15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2005)


Information extraction from semi-structured documents requires to find n-ary queries in trees that define appropriate sets of n-tuples of nodes. We propose new representation formalisms for n-ary queries by tree automata that we prove to capture MSO. We then investigate n-ary queries by unambiguous tree automata which are relevant for query induction in multi-slot information extraction. We show that this representation formalism captures the class of n-ary queries that are finite unions of Cartesian closed queries, a property we prove decidable.
  • Information extraction
  • semistructured documents
  • node selecting queries in trees


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