Indexed language

About: Indexed language is a research topic. Over the lifetime, 334 publications have been published within this topic receiving 11000 citations.

Some restrictive devices for context-free grammars

Abstract: For context-free grammars the restrictive devices of unordered scattered context, random context, partial ordering of productions and concatenation of productions in matrices are compared with respect to their generative power. This leads to two new characterizations of the family of type O languages in terms of unordered scattered context grammars and random context grammars, respectively. Languages generated by context-free grammars by imposing one of the above-mentioned restrictive devices or programming, regular control language, periodic time-variance or context-sensitivity are shown to have in the case of finite index a property similar to the “uvwxyproperty≓ of context-free languages.

Linear Context-Free Rewriting Systems and Deterministic Tree-Walking Transducers

Abstract: We show that the class of string languages generated by linear context-free rewriting systems is equal to the class of output languages of deterministic tree-walking transducers. From equivalences that have previously been established we know that this class of languages is also equal to the string languages generated by context-free hypergraph grammars, multicomponent tree-adjoining grammars, and multiple context-free grammars and to the class of yields of images of the regular tree languages under finite-copying top-down tree transducers.

Symbol-Relation Grammars

Abstract: A common approach to the formal description of pictorial and visual languages makes use of formal grammars and rewriting mechanisms. The present paper is concerned with the formalism of Symbol?Relation Grammars (SR grammars, for short). Each sentence in an SR language is composed of a set of symbol occurrences representing visual elementary objects, which are related through a set of binary relational items. The main feature of SR grammars is the uniform way they use context-free productions to rewrite symbol occurrences as well as relation items. The clearness and uniformity of the derivation process for SR grammars allow the extension of well-established techniques of syntactic and semantic analysis to the case of SR grammars. The paper provides an accurate analysis of the derivation mechanism and the expressive power of the SR formalism. This is necessary to fully exploit the capabilities of the model. The most meaningful features of SR grammars as well as their generative power are compared with those of well-known graph grammar families. In spite of their structural simplicity, variations of SR grammars have a generative power comparable with that of expressive classes of graph grammars, such as the edNCE and the N-edNCE classes.

Parallel context-free languages

Abstract: Parallel context-free languages are generated by context-free grammars in which every occurrence of a nonterminal in a line of derivation is rewritten simultaneously by the same rule. It is shown that the intersection of parallel context-free languages and context-free languages is the class of derivationbounded languages. Also, the parallel context-free languages form a proper subclass of the context-sensitive languages and are closed under union, product, Kleene closure, and homomorphism. An intercalation theorem is proved for parallel context-free languages.