Erzsébet Csuhaj-Varjú

Grammar Systems: A Grammatical Approach to Distribution and Cooperation

From the Publisher: This book investigates two major systems: firstly, cooperating distributed grammar systems, where the grammars work on one common sequential form and the cooperation is realized by the control of the sequence of active grammars; secondly, parallel communicating grammar systems, where each grammar works on its own sequential form and cooperation is done by means of communicating between grammars. The investigation concerns hierarchies with respect to different variants of cooperation, relations with classical formal language theory, syntactic parameters such as the number of components and their size, power of synchronization, and general notions generated from artificial intelligence.

Networks of Parallel Language Processors

A network of language processors (an NLP system) consists of several language identifying devices (language processors) associated with nodes of a network (in particular case with nodes of a virtual complete graph). The processors rewrite strings (representing the current state of the nodes) according to some prescribed rewriting mode and communicate them along the network via input and output filter languages. In this paper we study properties of NLP systems with L systems in the nodes.

P Automata or Purely Communicating Accepting P Systems

In this paper we introduce the notion of a Pautomaton with one-way communication, a concept related both to Psystems and the traditional concept of automata. A Pautomaton with one-way communication is a purely communicating accepting P system. The result of the computation in these systems is the set of multiset sequences consumed by the skin membrane, supposing that the Pautomaton started functioning in an initial state and entered a so-called final state. As a result, we show that for any recursively enumerable language, a Pautomaton and a certain type of projection can be constructed such that the given language is obtained as the image of the set of accepted input multiset sequences of the Pautomaton.

P automata

In this paper we discuss P automata, i.e., accepting P systems, using in most cases only communication rules. We briefly describe the most important variants of these systems and report on their important properties, with special emphasis on their computational power and size. We also propose some new topics and problems for future research.

Evolutionary systems : a language generating device inspired by evolving communities of cells

Abstract. We introduce a language generating device based on string operations suggested by the evolution of cell populations, called evolutionary system. Cells are represented by strings which describe their DNA sequences. The cell community evolves according to gene mutations and cell divison defined by operations on strings. The paper deals with the generative power of these mechanisms (a characterization of the class of recursively enumerable languages is presented) and the dynamics of the string population. A connection between the growth function of D0L systems and the population growth relation of evolutionary systems is also given.

On the Computational Complexity of P Automata

We characterize the classes of languages over finite alphabets which may be described by P automata, i.e., accepting P systems with communication rules only. Motivated by properties of natural computing systems, and the actual behavior of P automata, we study computational complexity classes with a certain restriction on the use of the available workspace in the course of computations and relate these to the language classes described by P automata. We prove that if the rules of the P system are applied sequentially, then the accepted language class is strictly included in the class of languages accepted by one-way Turing machines with a logarithmically bounded workspace, and if the rules are applied in the maximally parallel manner, then the class of context-sensitive languages is obtained.

Hybrid networks of evolutionary processors are computationally complete

Abstract.A hybrid network of evolutionary processors (an HNEP) consists of several language processors which are located in the nodes of a virtual graph and able to perform only one type of point mutations (insertion, deletion, substitution) on the words found in that node, according to some predefined rules. Each node is associated with an input and an output filter, defined by some random-context conditions. After applying in parallel a point mutation to all the words existing in every node, the new words which are able to pass the output filter of the respective node navigate simultaneously through the network and enter those nodes whose input filter they are able to pass. We show that even the so-called elementary HNEPs are computationally complete. In this case every node is able to perform only one instance of the specified operation: either an insertion, or a deletion, or a substitution of a certain symbol. We also prove that in the case of non-elementary networks, any recursively enumerable language over a common alphabet can be obtained with an HNEP whose underlying structure is a fixed graph depending on the common alphabet only.

Languages of colonies

Abstract A colony is a finite set of regular grammars, where each grammar generates a finite language. The component grammars cooperate to derive a common language. In this paper we compare the generative power of colonies with two cooperation strategies and with several types of the selection of the alphabet for the common language. The results give representations of languages of colonies in terms of classes of sequential and parallel languages.

Team behaviour in eco-grammar systems

EGO-grammar systems (EC systems) have been introduced in [2] for modelling syntactic properties of ecosystems. In this paper simple EC systems are discussed, which have n agents and, at each derivation step, k (or 6k) of the agents are active. The behaviour of a simple EC system is characterized by a language (of the environment), i.e. by a set of strings describing developmental stages of the system. We compare corresponding language classes 8_Y(n, =k) and 8Y(n, <k) for different values n and k. @ 1998 -Elsevier Science B.V. All rights reserved

P colonies with a bounded number of cells and programs

We continue the investigation of P colonies, a class of abstract computing devices composed of very simple agents (computational tools), acting and evolving in a shared environment. We show that if P colonies are initialized by placing a number of copies of a certain object in the environment, then they can generate any recursively enumerable set of numbers with a bounded number of cells, each cell containing a bounded number of programs (of bounded length), for constant bounds.