License: Creative Commons Attribution 3.0 Unported license (CC BY 3.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.ICDT.2019.13
URN: urn:nbn:de:0030-drops-103155
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Peterfreund, Liat ; Cate, Balder ten ; Fagin, Ronald ; Kimelfeld, Benny

Recursive Programs for Document Spanners

LIPIcs-ICDT-2019-13.pdf (0.6 MB)


A document spanner models a program for Information Extraction (IE) as a function that takes as input a text document (string over a finite alphabet) and produces a relation of spans (intervals in the document) over a predefined schema. A well-studied language for expressing spanners is that of the regular spanners: relational algebra over regex formulas, which are regular expressions with capture variables. Equivalently, the regular spanners are the ones expressible in non-recursive Datalog over regex formulas (which extract relations that constitute the extensional database). This paper explores the expressive power of recursive Datalog over regex formulas. We show that such programs can express precisely the document spanners computable in polynomial time. We compare this expressiveness to known formalisms such as the closure of regex formulas under the relational algebra and string equality. Finally, we extend our study to a recently proposed framework that generalizes both the relational model and the document spanners.

BibTeX - Entry

  author =	{Liat Peterfreund and Balder ten Cate and Ronald Fagin and Benny Kimelfeld},
  title =	{{Recursive Programs for Document Spanners}},
  booktitle =	{22nd International Conference on Database Theory (ICDT 2019)},
  pages =	{13:1--13:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-101-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{127},
  editor =	{Pablo Barcelo and Marco Calautti},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{},
  doi =		{10.4230/LIPIcs.ICDT.2019.13},
  annote =	{Keywords: Information Extraction, Document Spanners, Polynomial Time, Recursion, Regular Expressions, Datalog}

Keywords: Information Extraction, Document Spanners, Polynomial Time, Recursion, Regular Expressions, Datalog
Collection: 22nd International Conference on Database Theory (ICDT 2019)
Issue Date: 2019
Date of publication: 19.03.2019

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