Petri Net Formalism Research Articles

A comparison of temporal Petri net techniques in the specification and design of hard real-time systems

This paper assesses the suitability of two techniques, based on Petri nets and temporal logic, for the specification, design and verification of a real-time industrial control system that forms part of a high speed packaging machine. It presents a brief overview of Petri nets and temporal logic and describes how the strengths of both techniques are captured in the combined formalism of temporal Petri nets. The paper discusses the advantages of using temporal Petri nets and an extended form of temporal Petri nets in specification and design. These techniques are applied to the specification and design of control and synchronisation logic for a flexible manufacturing system comprising loosely coupled asynchronous mechanisms. It is shown that the problem can be specified elegantly using Petri nets, the verification of the specification can be completely carried out using temporal logic, and the specification can be evolved into a design in such a manner that the design inherits the specified properties.

Petri nets based approach to software development for real-time control

Indexing terms: Software development, Petri nets, Real-time control Abstract: An approach to software development for real-time control is presented. The Petri nets formalism is used in the specification phase to describe the concurrency and synchronisation aspects of the software environment. Then the resulting Petri net model is implemented by means of a data driven architecture and can be based on any standard high-level language. The software development procedure described has been followed by a number of users for the rapid production, debugging, testing and prototyping of software modules.

Prism-methodology and process-oriented environment

The Prism model of engineering processes and an architecture which captures this model in its various components are described. The architecture has been designed to hold a product software process description the life-cycle of which is supported by an explicit representation of a higher-level (or meta) process description. The central part of this paper describes the nine-step Prism methodology for building and tailoring process models and gives several scenarios to support this description. In Prism, process models are built using a hybrid process modeling language that is based on a high-level Petri net formalism and rules. An important observation is that this environment should be seen as an infrastructure for carrying out the more difficult task of creating sound process models.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A unified high-level Petri net formalism for time-critical systems

The authors introduce a high-level Petri net formalism-environment/relationship (ER) nets-which can be used to specify control, function, and timing issues. In particular, they discuss how time can be modeled via ER nets by providing a suitable axiomatization. They use ER nets to define a time notation that is shown to generalize most time Petri-net-based formalisms which appeared in the literature. They discuss how ER nets can be used in a specification support environment for a time-critical system and, in particular, the kind of analysis supported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling temporal processes via belief networks and Petri nets, with application to expert systems

We show how Bayesian belief networks (BNs) can be used to model common temporal knowledge. Two approaches to their structuring are proposed. The first leads to BNs with nodes representing states of a process and times spent in such states, and with a graphical structure reflecting the conditional independence assumptions of a Markovian process. A second approach leads to BNs whose topology represents a conditional independence structure between event-times. Once required distributional specifications are stored within the nodes of a BN, this becomes a powerful inference machine capable, for example, of reasoning backwards in time. We discuss computational difficulties associated with propagation algorithms necessary to perform these inferences, and the reasons why we chose to adopt Monte Carlo-based propagation algorithms. Two improvements to existing Monte Carlo algorithms are proposed; an enhancement based on the principle of importance sampling, and a combined technique that exploits both forward and Markov sampling. Finally, we consider Petri nets, a very interesting and general representation of temporal knowledge. A combined approach is proposed, in which the user structures temporal knowledge in Petri net formalism. The obtained Petri net is then automatically translated into an equivalent BN for probability propagation. Inferred conclusions may finally be explained with the aid of Petri nets again.

Expertext: From semantic nets to logic Petri nets

Hypertext systems present textual information in an intuitive way, while expert systems logically solve problems. Expertext is an approach to combining the precision of expert reasoning processes with the browsing capabilities afforded by hypertext. In this paper intelligent hypertext is first modeled with a semantic net. The semantic net formalism is then extended to a Petri net formalism. Finally, a deductive inferencing ability is added to the Petri net formalism. Examples of how an Electronic Yellow Pages might exploit these methods are presented.

A Software Production Methodology for Process Control

In this paper a software production methodology for process control is presented. The specification phase is carried out by resorting to the formalism of Petri Nets. By means of a worked example it is shown how Petri Nets are amenable to describe feedback control structures. The implementation of Petri Net models is performed by the use of a data driven architecture. The presence of system tasks supplying standard functions, such as monitor, display, command acquisition is also considered to ease software production.

Representation of assembly and automatic robot planning by Petri net

The author proposes an approach to represent assembly by Petri nets and presents an algorithm of automatic robot assembly planning based on the Petri-net model. The Petri-net model of assembly is configured by the goal structures and initial constraints, both in the Petri-net formalism. Due to the Petri-net representation of assembly, the plan generation is quite straightforward and the planning algorithm can be easily and efficiently implemented with simple matrix manipulation. An example of how to plan an assembly by the Petri net model is presented. >

Symbolic execution of concurrent systems using Petri nets

Techniques for analyzing sequential programs in order to improve their reliability have been widely studied in the past. Among the most interesting analysis techniques, we consider symbolic execution. However, analysis techniques for concurrent programs, and in particular symbolic execution, are still an open research area. In this paper, we define a method for symbolic execution of concurrent systems, based on an extension of the Petri net formalism, called EF nets. EF nets are a powerful, highly expressive and general formalism. Depending on the level of abstraction of actions and predicates that one associates to the transitions of the net, EF nets can be used as a high-level specification formalism for concurrent systems, or as a lower level internal representation of concurrent programs. Thus, the model is not dependent on a particular concurrent programming language, but it is flexible enough to be the kernel model for the representation of a wide set of systems and programming languages. In the paper, in order to support the analysis of a concurrent system or program, at first a general algorithm for symbolically executing an EF net is defined. Then, a more efficient algorithm is given for the particular, though important, subclass of EF nets, defined as safe EF nets. Such algorithm is proved to significantly help in reducing the amount of information needed to characterize a symbolic execution. Both the modelling power of the EF nets and the usefulness of the concurrent symbolic execution algorithms defined are illustrated by means of a case study.

Modeling and analysis of the behavior of information systems

Many widely used specification techniques for information systems are based on a hierarchy of information flow diagrams. A method is introduced which preserves the benefits of these techniques and adds the precision of the Petri net formalism. Information-flow diagram hierarchies are formalized by notions of net theory. The bottom-level nets of a hierarchy are treated as Petri nets. The behavior model of the information system is the Petri net derived by repeatedly replacing each part of a net by its associated refinement. As a prerequisite for such replacements, the data abstractions relation information flows of different level are specified by a semantic hierarchy data model. The nets in the hierarchy are appended by dynamic counterparts of the abstractions so that a consistent replacement becomes possible. The interface behavior of the nets in the hierarchy is analyzed, using the concept of behavior constraints as a formal measure of correct interface behavior. The behavior model can be derived in an iterative bottom-up way by first analyzing a net for fulfillment of its associated behavior constraint and afterward integrating it into the next-higher-level net. >

Non-deterministic modelling of logical queries in deductive databases

We propose a technique based on Petri Nets formalism to model logic queries in deductive databases. The model is called PNLP (Petri Net model for Logic Programs), and it has a simple formal description and a graphical representation. The PNLP model explicitly represents the relationships between rules and predicates. It is general and flexible enough to demonstrate the flow of control in different algorithms used to evaluate recursive logic queries. In fact the model unifies the level of description of these algorithms, and facilitates identifying similarities and differences between them. The inherent non-determinism in the PNLP model may also be useful in recognizing the parallelism within Horn-clause logic programs. In this paper, the PNLP model is described, and its functionality is demonstrated by modeling several existing algorithms for recursive query evaluation.

Directed graph based representation for software system design

In this paper, a model for representing and analysing the design of a software system is proposed. The scheme is based on Petri net formalism and allows representation of both control and data flows in an integrated manner. Both the structure and the behaviour of the system can be modelled using this scheme. Analysis and verification of some behavioural properties provide a certain degree of design validation prior to implementation.

Petri net representation of decision models

Models of decision-making organizations supported by command, control, and communication systems are represented using the Petri net formalism. A small set of primitives, defining the correspondence between decision models, signals, and functions and their Petri net counterparts, is proposed. A new decision signal-routing demultiplexer is added to the Petri net formalism to represent internal decision-making in the model. Using the above primitives, any decision-making structure can be modeled by a Petri net diagram. An array is introduced that describes the interactions between decision-makers, and an algorithm is presented for the calculation of delay when synchronous protocols are used.

Modeling and Analysis of Distributed Database Concurrency Control Algorithms Using an Extended Petri Net Formalism

Distributed database systems (DDBS) have received considerable attention in recent years. Being a relatively young research field, there are still many problems associated with DDB systems that need solution. Concurrency control is one of these problems and, probably, the most extensively studied. However, most of the work has concentrated on the development of alternative solutions and the field seems to be ready for some comparative analysis work. This paper reports the results of a performance evaluation study on distributed database concurrency control algorithms. The research has resulted in the development of a formalism, based on Petri nets, for modeling and analysis purposes. The formalism, called the Extended Place/Transition Nets (EPTN), is both descriptively powerful in that it can be used to model various algorithms precisely and succinctly and to communicate them in a clear manner, while at the same time lending itself to be used as a performance evaluation tool. An EPTN simulator is implemented and various algorithms are studied using this tool. This paper describes both the formalism and the performance results that have been obtained.

Delta Semantics Defined by Petri Nets

&lt;p&gt;Delta is a language designed for general system description. It is partly built upon Simula, but is more than a programming language, since it contains several features, which cannot be implemented on a computer system. E.g. a continuous time concept, concurrency between an unbounded number of components and the possibility of using predicates to specify state changes.&lt;/p&gt;&lt;p&gt;In this paper a formal semantics for Delta is defined and analysed using Petri nets. Petri nets were chosen because the ideas behind Petri nets and Delta coincide on several points.&lt;/p&gt;&lt;p&gt;A number of proposals for changes in Delta, which resulted from this work, are also reported here, whereas a number of extensions to the Petri net formalism may be found in [Jensen 78] (DAIMI TR-5).&lt;/p&gt;&lt;p&gt;Revised version. 137 pp&lt;/p&gt;&lt;p&gt;DELTA Project Report No, 12&lt;/p&gt;