On restricted context-free grammars

Abstract

In context-free grammars, each derivation step can be characterized so that (i) a nonterminal of the current sentential form is chosen and (ii) rewritten by a rule. However, it is well-known that context-free grammars are not able to cover all aspects of natural languages and/or programming languages. Therefore, there were defined many grammars with context-free rules and some mechanism controlling the application of rules, e. g., in random context grammars and their variants, a rule is only applicable if the current sentential form contains some letters or subwords and some letters or words do not occur in it. Therefore, in grammars controlled by context, each derivation step can be characterized so that (i) subsets of applicable nonterminals and rules are determined according to the symbols appearing in the current sentential form, (ii) an applicable nonterminal is chosen and (iii) rewritten by an applicable rule. © 2010 Springer-Verlag Berlin Heidelberg.