On restricted context-free grammars

0367493 - MÚ 2012 RIV US eng J - Journal Article
Dassow, J. - Masopust, Tomáš
On restricted context-free grammars.
Journal of Computer and System Sciences. Roč. 78, č. 1 (2012), s. 293-304. ISSN 0022-0000. E-ISSN 1090-2724
Institutional research plan: CEZ:AV0Z10190503
Keywords : context-free grammars * derivation restriction * normal forms
Subject RIV: BA - General Mathematics
Impact factor: 1.000, year: 2012
http://www.sciencedirect.com/science/article/pii/S0022000011000572

Context-free grammars are widely used for the simple form of their rules. A derivation step consists of the choice of a nonterminal of the sentential form and of an application of a rule rewriting it. Several regulations of the derivation process have been studied to increase the power of context-free grammars. In the resulting grammars, however, not only the symbols to be rewritten are restricted, but also the rules to be applied. In this paper, we study context-free grammars with a simpler restriction where only symbols to be rewritten are restricted, not the rules, in the sense that any rule rewriting the chosen nonterminal can be applied. We prove that these grammars have the same power as random context, matrix, or programmed grammars. We also present two improved normal forms and discuss the characterization of context-sensitive languages by a variant using strings of length at most two instead of symbols.
Permanent Link: http://hdl.handle.net/11104/0202154