Journal of Logic, Language and Information

, Volume 17, Issue 3, pp 345–381

Highly Constrained Unification Grammars

Article

DOI: 10.1007/s10849-008-9062-9

Cite this article as:
Feinstein, D. & Wintner, S. J of Log Lang and Inf (2008) 17: 345. doi:10.1007/s10849-008-9062-9

Abstract

Unification grammars are widely accepted as an expressive means for describing the structure of natural languages. In general, the recognition problem is undecidable for unification grammars. Even with restricted variants of the formalism, off-line parsable grammars, the problem is computationally hard. We present two natural constraints on unification grammars which limit their expressivity and allow for efficient processing. We first show that non-reentrant unification grammars generate exactly the class of context-free languages. We then relax the constraint and show that one-reentrant unification grammars generate exactly the class of mildly context-sensitive languages. We thus relate the commonly used and linguistically motivated formalism of unification grammars to more restricted, computationally tractable classes of languages.

Keywords

Unification grammarsLinear indexed grammarsMildly context- sensitive languagesGenerative capacity

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Department of Computer ScienceUniversity of HaifaHaifaIsrael