Strongly Regular Grammars and Regular Approximation of Context-Free Languages

Authors:
Ömer Eğecioğlu
Affiliations:
Department of Computer Science, University of California, Santa Barbara 93106
Venue:
DLT '09 Proceedings of the 13th International Conference on Developments in Language Theory
Year:
2009

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Abstract

We consider algorithms for approximating context---free grammars by regular grammars, making use of Chomsky's characterization of non---self---embedding grammars as generating regular languages and a transformation by Mohri and Nederhof on sets of mutually recursive nonterminals. We give an exposition of strongly regular grammars and this transformation, and use it as a subprocedure to obtain tighter regular approximations to a given context-free grammar. In another direction, the generalization by a 1---lookahead extends Mohri and Nederhof's transformation by incorporating more context into the regular approximation at the expense of a larger grammar.