Showing papers on "Petri net published in 1978"

Self-Modifying Nets, a Natural Extension of Petri Nets

Abstract: In this paper we study a natural extension of Petri nets and discuss the usefullness of this approach. Like ordinary Petri nets self-modifying nets are defined as multigraphs having edges of the form O q >I and I q >O " Circles denote places and bars represent transitions. But in opposition to ordinary Petri nets q may be either the number I or an arbitrary place p of the net. If q = I, as in the case of a Petri net, firing the transition means~ that one token has to be moved from or to the place. But if q is a place p, then the number of tokens to be moved equals the actual number of tokens in p and thus depends on the actual marking. If for an actual marking M we define n := IF qEP THEN M(q) ELSE q and substitute q by n, we obtain a Petri net and the firing rule for that marking is defined as usually. Therefore a self-modifying net is a Petri net, which is able to modify its own firing rules. Bounded models of such nets have been used to simulate national economic systems /Fu/.

Properties of Conflict-Free and Persistent Petri Nets

Abstract: Petri nets have been extensively studied because of their suitability as models for asynchronous computing Despite this effort, the mathematical properties of Petrl nets are not very well understood In this paper we investigate two unportant special types of Petn nets, the conflict-free nets and the persistent nets, the former being a proper subset of the latter. Our results completely characterize the sets of reachable markings attainable by such nets Reachabihty sets of persistent nets are shown to be semllmear A stronger result is obtamed for conflict-free nets which results m an exponential time algorithm for deciding boundedness of such nets The best known upper bound for deciding boundedness of arbitrary nets is exponential space We conclude with a proof that all reachablhty sets of Petri nets may be realized with a "small amount" of nonperslstence

Use of production systems for modeling asynchronous, concurrent processes

Abstract: Because of the event-driven nature of asynchronous, concurrent processes, production systems (PSs) are an attractive modeling tool. The system of interest can be modeled with a large number of independent states, with independent actions, and the knowledge base can be conveniently encoded declaratively. However, asynchronous, concurrent processes normally have strict requirements for interprocess communication and coordination; this requires a substantial degree of interrule communiation in the PS. The result of this is that a complex control structure is embedded in the short-term memory (STM); this is generally considered unattractive for a number of reasons. This chapter proposes a separate, explicit control structure for modeling asynchronous, concurrent processes with PSs. Specifically, the use of a Petri net is addressed. A system of asynchronous, concurrent processes can be modeled using PSs to model the individual processes or events and using a Petri net to model the relationships between the processes. Furthermore, a hierarchy of such networks is proposed; an allowable production rule action is the instantiation of another network. This is supported with a structured, hierarchial STM.

Synchronized petri nets : A model for the description of non-autonomous sytems

Abstract: We introduce and study the functioning of non-autonomous Petri Nets (PN). The Synchronized Petri Nets (SPN) are defined as being PN's such that transition finings are synchronized on the occurrences of external events. We show that the nesults concerning the verification of characteristic properties (eive, bounded, persistent) by autonomous PN's are only partially valid for this mode of functioning. The model of Labeled SPN is proposed and studied as a tool for the description and analysis of non-autonomous systems.

Design and verification of communication procedures: A bottom-up approach

Abstract: The verification of functional specifications is performed by means of a formal model, based upon Petri nets. A so-called "reduction" operation is introduced to handle the concept of abstraction. A bottom-up approach is developped in the case of communication between two processors. The definition of software modules is emphasized.

Towards the performance evaluation of distributed computing systems

Abstract: The aims of this paper are twofold. Firstly, it aims to describe progress towards the development of a performance modelling technique which is appropriate to problems involving communicating parallel activities. Secondly, in doing this, it aims to provide an example of how differing areas of research may be related to their mutual benefit, and to indicate how facets of them may be combined to provide a valuable design tool. We draw on two current areas of research: a method of expression of concurrent activities in a programming language called EPL; and analytical performance modelling techniques based on probabilistic grammars, finite state machines and computation structures. These two areas are brought together by re-casting salient features in Petri net form. Only a sub-class of Petri nets is needed, giving valuable properties which are exploited in determining the extent to which current analytical techniques can be used. A method of modelling using these techniques in combination with simulation techniques is proposed.

An asynchronous logic array for the realisation of logic systems with concurrency

Abstract: An array circuit able to implement any logic system described by a Petri net is presented. It uses a request acknowledge asynchronous functioning mode and constitutes a simplification of a solution proposed by Patil previously.

A Modular Computer With Petri Net Array Control

Abstract: This paper presents a computer system with modular functional units which establishes data and control paths dynamically by means of a programmable Petri net array The input program control flow and the desired allocation of hardware resorces are specified by means of a Petri net and the array by realizing this net controls the data flow between the functional unit The system exploits parallelism present in the hardware and the program to the extent specified by the programmer Some of the advantages of the present approach are that the program status is reflected by the array status, and hence can be monitored by observing the latter and that precise resource allocation/scheduling can be enforced by the user

Petri nets as a modeling tool for discrete concurrent tasks of the human operator

Abstract: The basic concepts of Petri nets are reviewed as well as their application as the fundamental model of technical systems with concurrent discrete events such as hardware systems and software models of computers. The use of Petri nets is proposed for modeling the human operator dealing with concurrent discrete tasks. Their properties useful in modeling the human operator are discussed and practical examples are given. By means of and experimental investigation of binary concurrent tasks which are presented in a serial manner, the representation of human behavior by Petri nets is demonstrated.

Petri nets as a modeling tool for discrete concurrent tasks of the human operator. [describing sequential and parallel demands on human operators

Abstract: The basic concepts of Petri nets are reviewed as well as their application as the fundamental model of technical systems with concurrent discrete events such as hardware systems and software models of computers. The use of Petri nets is proposed for modeling the human operator dealing with concurrent discrete tasks. Their properties useful in modeling the human operator are discussed and practical examples are given. By means of and experimental investigation of binary concurrent tasks which are presented in a serial manner, the representation of human behavior by Petri nets is demonstrated.

Predicting concurrent computer system performance using Petri-Net models

Abstract: A method for efficiently employing Petri-Net models to predict performance of concurrent computer architectures is presented. The feasibility of such methods for use as architectural design tools is demonstrated, and the model's properties are discussed.