Indexed language

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

Homomorphic Images os Sentential Forms and Terminating Grammars (Extended Abstract)

Abstract: We consider languages generated as homomorphic images of sentential form languages and related grammars. A characterization of these languages in terms of their topological properties is given. Previous hierarchy results are strengthened by constructing separating languages over a single letter alphabet. The relation to languages generated by terminating grammars is investigated.

Timed languages, dyadic approximations and regular tree grammars

Abstract: Our research on the modelization of the loop actionperception for an autonomous robot has led us naturally towards a tree-like representation of that interaction: a node is labeled by a perceptive context of the robot, the different branches correspond to the various available actions and the children nodes are then the effect of these different actions on the original context. This tree-like view allows us to state rigorously the problems of viable control in terms of games: the existence of a controller is reduced to the existence of strategies which allow to walk through the trees representing the system in order to remain within a given class of contexts (viability goal). Such game approaches are widely used in computer science (BL69; Mos89; NYY92), and appear in hybrid control theory too (TLS98). Furthermore it is necessary to describe these tree sets as simply as possible, in order to decide for the existence of a controller, and in the best case to synthesize such a controller (The95). In this paper, we study timed automata from the point of view of regular tree grammars showing how our approach can be applied to this central class of decidable hybrid systems.

Derivation Languages of Graph Grammars

Abstract: We investigate sequential derivation languages associated with graph grammars, as a loose generalisation of free-labeled Petri nets and Szilard languages. The grammars are used to output strings of rule labels, and the applicability of a special rule determines the acceptance of a preceding derivation. Due to the great power of such grammars, this family of languages is quite large and endowed with many closure properties. All derivation languages are decidable in nondeterministic polynomial time and space O(n log n), by simulation of the graph grammar on a Turing machine.

An NC algorithm for recognizing tree adjoining languages

Abstract: A parallel algorithm is presented for recognizing the class of languages generated by tree adjoining grammars, a tree rewriting system which has applications in natural language processing. This class of languages is known to properly include all context-free languages; for example, the noncontext-free sets {a n b n c n } and {ww} are in this class. It is shown that the recognition problem for tree adjoining languages can be solved by a concurrent read, concurrent write parallel random-access machine (CRCW PRAM) inO(logn) time using polynomially many processors. Thus, the class of tree adjoining languages is inAC 1 and hence inNC. This extends a previous result for context-free languages.

Trees as contexts in formal language generation

Abstract: Initially designed to generate languages without rewriting of some nonterminals, contextual grammars are used in formal language theories as well as models for several particular aspects of natural languages However, despite their power, contextual grammars do not provide a structural description of the generated languages We present several modalities to add structures to classical contextual grammars We are studying the relations of these structured contextual languages comparing with other structured languages Several examples show the potential of the newly introduced grammars