Abstract
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.
Original language | English |
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Title of host publication | 22nd International Conference on Database Theory, ICDT 2019 |
Editors | Pablo Barcelo, Marco Calautti |
Publisher | Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing |
ISBN (Electronic) | 9783959771016 |
DOIs | |
State | Published - Mar 2019 |
Externally published | Yes |
Event | 22nd International Conference on Database Theory, ICDT 2019 - Lisbon, Portugal Duration: 26 Mar 2019 → 28 Mar 2019 |
Publication series
Name | Leibniz International Proceedings in Informatics, LIPIcs |
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Volume | 127 |
ISSN (Print) | 1868-8969 |
Conference
Conference | 22nd International Conference on Database Theory, ICDT 2019 |
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Country/Territory | Portugal |
City | Lisbon |
Period | 26/03/19 → 28/03/19 |
Bibliographical note
Publisher Copyright:© Liat Peterfreund, Balder ten Cate, Ronald Fagin, and Benny Kimelfeld.
Keywords
- Datalog
- Document spanners
- Information extraction
- Polynomial time
- Recursion
- Regular expressions