Showing papers on "Process architecture published in 1990"

Petri nets are moniods

Abstract: Petri nets are widely used to model concurrent systems. However, their composition and abstraction mechanisms are inadequate: we solve this problem in a satisfactory way. We start by remarking that place/transition Petri nets can be viewed as ordinary, directed graphs equipped with two algebraic operations corresponding to parallell and sequential composition of transitions. A distributive law between the two operations captures a basic fact about concurrency. New morphisms are defined, mapping single, atomic transitions into whole computations, thus relating system descriptions at different levels of abstraction. Categories equipped with products and coproducts (corresponding to parallel and nondeterministic compositions) are introduced for Petri nets with and without initial markings. Petri net duality is expressed as a duality functor, and several new invariants are introduced. A tensor product is defined on nets, and their category is proved to be symmetric monoidal closed. This construction is generalized to a large class of algebraic theories on graphs. These results provide a formal basis for expressing the semantics of concurrent languages in terms of Petri nets. They also provide a new understanding of concurrency in terms of algebraic structures over graphs and categories that should apply to other models besides Petri nets and thus contribute to the conceptual unification of concurrency.

On the hierarchical modeling analysis and simulation of flexible manufacturing systems with extended Petri nets

Abstract: A class of Petri nets, called extended Petri nets, with multiple types of places, multiple classes of tokens and multiple arcs is proposed. It is utilized for the hierarchical modeling of flexible manufacturing systems, ensuring a priori that the extended Petri net system model obtained is live, bounded, consistent and error free. The proposed method views the operation of the flexible manufacturing system as a process that is decomposed into operations with specified precedence relations. For each operation the required resources are identified, and on the basis of these requirements the overall system is decomposed into a set of finite subsystems. The operation of each subsystem is modeled as an event graph representing a single resource activity cycle. The extended Petri net system model is synthesized from these component nets using certain synthesis rules. A software package has been developed to simulate the execution of the model obtained. >

Petri net objects for the design, validation and prototyping of user-driven interfaces

Abstract: Petri Net Objects (P.N.O.) are a high-level, object-structured dialect of Petri nets, primarily devised for the design of parallel systems. We show how this formalism can be used for the specification and design of event-driven interfaces, through the use of a real-life example. We then discuss the potential for dialogue validation, integration in UIMS and prototyping offered by this model.

Computer-aided generation of programs modelling complex systems using colored petri nets

Abstract: A method and system in which a programmed digital computer serving as a graphical "engine" is employed to construct an executable model for a complex system using a hierarchy of so called "Colored" Petri nets (CPN's or CP-nets) The operation of the complex system is specified in terms of a graphical net structure and formal net inscriptions, such as arc expressions and guards, which ensure development of a program, or executable model, and associated data structures, properly defining the system Sophisticated syntax checks and other tools are provided for ensuring that the model so constructed conforms to a set of rules which guarantee valid system behavior

Formal analysis of the alternating bit protocol by temporal Petri nets

Abstract: Temporal Petri nets are Petri nets in which certain restrictions on the firings of transitions are represented by formulas containing temporal operators. The use of temporal Petri nets for formal specification and verification of the alternating bit protocol is discussed. The temporal Petri net which models the protocol is analyzed formally using the existing theory of omega -regular expressions and Buchi-automata. >

Transformation methods for generalized Petri nets and their applications to flexible manufacturing systems

Abstract: Transformation methods are presented for generalized Petri nets by introducing and using the concept of a live and bounded circuit (LB-circuit). An LB-circuit is a generalized version of a simple elementary circuit. The authors also introduce the concept of an arc ratio, which is defined by the arcs' relations in an LB-circuit and is closely related to the liveness and boundedness of the net. The overlapping relation between two directed paths has an effect on the loss or increase of tokens in the net. Three transformation theorems are given for synthesis and reduction using these concepts. These theorems are used for reducing or synthesizing generalized Petri nets while preserving the liveness and boundedness of the net. The methods consider the dynamic behavior and structure of the net at the same time. The synthesis methods are illustrated for the design of a simple FMS (an assembly process with three robots and two workstations). >

Petri Nets as Models of Linear Logic

Abstract: The chief purpose of this paper is to appraise the feasibility of Girard's linear logic as a specification language for parallel processes. To this end we propose an interpretation of linear logic in Petri nets, with respect to which we investigate the expressive power of the logic.

A categorical linear framework for Petri nets

Abstract: This research brings together, in a methodical way, several approaches to giving a compositional theory of Petri nets using category theory and to the use of linear logic in specifying and reasoning about Petri nets. The authors construct categories of nets based on V.C.V. de Paiva's dialectica category models (1989) of linear logic in which they are able to exploit the structure of de Paiva's models to give constructions on categories of nets. Using a category of safe nets as an example, it is shown how this approach yields both existing and novel constructions on nets and their computational interpretation is discussed. The authors also indicate how more general categories of nets can be expressed in this framework. >

Partial order behaviour and structure of Petri nets

Abstract: This paper argues that partial order semantics can be used profitably in the proofs of some nontrivial results in Petri net theory. We show that most of Commoner's and Hack's structure theory of free choice nets can be phrased and proved in terms of partial order behaviour. The new proofs are considerably shorter (and, arguably, more lucid) than the old ones; they also generalise the results from (safe) free choice nets to (bounded) extended free choice nets.

Synthesis rules for Petri nets, and how they lead to new results

Abstract: Three kits of rules for top-down synthesis of Petri nets are introduced. The properties and expressive power of the kits are compared. They are then used to characterise the class of structurally live Free Choice nets by means of the rank of the incidence matrix.

CCS and Petri Nets

Abstract: In the usual semantics of CCS-like languages, parallelism is reduced to non-deterministic interleaving of actions. As an alternative semantic model for CCS with a clear distinction between concurrency and nondeterminism, Petri nets may be used. This paper gives an introduction to Petri net semantics for CCS. Two approaches are considered: a compositional approach where semantic operations are defined for Petri nets explicitly, and an operational approach using Plotkin-style transition rules which is particularly convenient for infinite processes. It is discussed which class of CCS programs is representable by finite nets.

System Modelling with Petri Nets

Abstract: Petri Nets (PN) are a graphical formalism which is gaining popularity in recent years as a tool for the representation of complex logical interactions (like synchronization, sequentiality, concurrency and conflict) among physical components or activities in a system. This notes are devoted to introduce the formalism of Petri nets with particular emphasis on the application of the methodology in the area of the performance and reliability modelling and analysis of systems. The quantitative analysis of the behaviour of systems in time requires the superposition of a stochastic timing mechanism to the classical representation of PN. Timed Petri nets and, in particular, Stochastic Petri nets (SPN) are the object of the second part of the notes. Finally, some fully developed examples enlighten peculiar aspects which differentiate PNs from other modelling techniques usual in reliability analysis. In few words, the goal of these notes is to show that the proposed methodology based on the PN formalism can be conveniently used as a user-friendly language to represent and evaluate complex stochastic systems.

A review of synthesis techniques for Petri nets

Abstract: Research results regarding synthesis techniques for Petri nets are reviewed. These methods can be adopted for modeling parallel and distributed application environments such as automated manufacturing systems to provide a solution for handling complex and concurrent interactions. Significant synthesis techniques, which are basically classified into bottom-up and top-down methods, are discussed. Bottom-up techniques, consisting of merging of places and sharing of simple elementary paths, have the advantage of ease of system description since the modeled subsystems usually have real-life correspondences. Nevertheless, with existing techniques the synthesized system may not exhibit the same control properties as the subsystems. Top-down methods, including refinement of transitions and refinement of places, have the advantage of viewing the system globally, which may generate more structured designs. However, it is difficult to apply these methods to environments with highly shared resources. Automated manufacturing system examples are given to demonstrate the applications of the methods. >

Applying Petri net reduction to support Ada-tasking deadlock detection

Abstract: The application of Petri net reduction to Ada-tasking deadlock detection is investigated. Net reduction can ease reachability analysis by reducing the size of the net while preserving relevant properties. By combining Petri net theory and knowledge of Ada-tasking semantics some specific efficient reduction rules are derived for Petri net models of Ada-tasking. A method by which a useful description of a detected deadlock state can be easily obtained from the reduced net's information is suggested. >

Advances in Petri Nets, 1989

Abstract: Stochastic Petri nets: An elementary introduction.- Improving the efficiency of the analysis of DSPN models.- Synchronized elementary net systems.- Descriptive and analytical process algebras.- P/T-systems as abstractions of C/E-systems.- The semantics of capacities in P/T nets.- Petri net tool overview 1989.- Equivalence transformations of PrT-Nets.- A reduction theory for coloured nets.- Optimizing microprograms for recurrent loops on pipelined architectures using timed Petri nets.- S-CORT(R): A method for the development of electronic payment systems.- Timed Petri nets and application to multi-stage production systems.- Petri net systems and their closure properties.- Occam and the transputer.- About the concurrent behaviour of EN systems: Definability and closure results.- Petri nets and flexible manufacturing.- Some properties of timed nets under the earliest firing rule.- A comparative study of different techniques for semi-flows computation in place/transition nets.- Elementary net systems and dynamic logic.- Representation of a swapping class by one net.- Design methods based on nets.- CEDISYS compositional distributed systems state of the art, research goals, references.

Knowledge based design flow management

Abstract: The knowledge regarding design flow management is described and modeled by predicate-transition Petri nets and production rules. The approach offers a clear and flexible tool control mechanism within a CAD framework such that both static and dynamic behavior of a design flow are supported. The authors also demonstrate how different forms of knowledge can be implemented by a rule based system, OPS83, and be integrated in the HILDA CAD framework to guide the users through the design process. >

Petri net based modelling of information flow security requirements

Abstract: An extended Petri net formalism which can be used to model information flow security requirements is described. The proposed framework can be used to specify a range of security policies by making specific choices for the components of the model. It is believed that Petri nets provide an elegant way of modeling security policies in a distributed system. The ability to model concurrency, the structural generality of Petri nets, and the existence of powerful analytical techniques make the Petri-net modeling approach even more useful. Two examples are given to illustrate the use of such a model. >

An integrated software development methodology based on hierarchical colored Petri Nets

Abstract: This paper presents a new integrated software development methodology that uses SADT diagrams, Hierarchical CP-nets, Standard ML, and automatic mechanisms for translating SADT diagrams into Hierarchical CP-nets and for converting Hierarchical CP-nets into Standard ML executable code. A case study describes the development of a software application called the Debt Manager's Assistant, which implements a non-FIFO strategy for electronic funds transfer. This application was built for the Marine Midland Bank of New York and Societe Generale. During application development, the requirements analysis and system specification were done with the aid of the Structured Analysis and Design Technique. The system design and verification used Hierarchical Colored Petri Nets and the implementation was supported with the automatic production of executable Standard Meta Language code.

An environment for specifying and executing hierarchical Petri nets

Abstract: An environment for the construction and execution of requirement specifications for embedded systems is described. High-order Petri nets are used as a notation for the specifications. The environment consists of a net browser, a net editor, an animated net simulator, and a simulation engine. A hierarchically structured specification can be constructed using the graphics-based net editor. The animated simulator helps to detect errors and inconsistencies. The net browser enables management of several net hierarchies and the retrieval and reuse of nets. The simulation engine allows specifications to be executed in real time in the real environment. The authors concentrate on the net browser and the concepts, methods, and graphical notations used for improving the usability of high-order Petri nets. >

Modeling and performance analysis of a resource-sharing manufacturing system using stochastic Petri nets

Abstract: The objectives of this work are to model a manufacturing system using top-down Petri net modeling approaches and mutual exclusion concepts; to construct stochastic Petri nets by considering the random failures of the machines, as well as such resources as robots and automated guided vehicle systems, and by incorporating temporal variables to transitions and places; to derive the performance of the system using stochastic Petri net performance models for different cases; and to compare performance results. Performance analysis problems on both deadlock-free and deadlock-prone systems are addressed and a comparison between them is made. First the stochastic Petri net modeling process is discussed on the basis of top-down and bottom-up ideas. Then, system performance indices, such as throughput for a resource-sharing manufacturing system, are derived by using existing software packages such as SPNP. Finally, conclusions are drawn and future directions are discussed for Petri net evaluation of manufacturing systems. >

Software Implementation of Petri nets and compilation of rule-based systems

Abstract: The aim of this paper is to discuss the issue of high-level Petri nets implementation. The specific class of high-level net considered is such that tokens are objects and transitions are rules with variables. They are a special case of Predicate/Transition nets. The implementation technique proposed here is an adaptation of the compilation technique developed for rule-based systems preserving the net structure. This technique is compared to the token-player algorithm, commonly used for centralized implementation as well as to a direct translation of the net into a rule-based system which is compiled afterwards.

Reachability of LSFC nets

Abstract: Free choice nets are a class of Petri nets that can represent the substantial features of systems by modeling both choice and concurrency. A reachability problem of live and safe free choice (LSFC) nets is considered. A necessary and sufficient condition for the reachability of a class of LSFC nets is presented. A structural analysis of LSFC nets is presented. >

An approach towards distributed simulation of timed Petri nets

Abstract: The authors present a model of timed Petri nets which is more general than known models in terms of modeling convenience. The model consists of simple but fairly general modules. This results in simpler and more modular codes for simulation of these systems, as compared with the known models of timed Petri nets. Time can be associated with either a place or a transition or both. The model consists of several simple modules resulting in modular code for simulation. The authors present an approach towards distributed simulation of the model. The well-known distributed simulation schemes for discrete event systems do not directly apply to these systems due to the nonautonomous nature of place nodes in timed Petri nets. The authors incorporate several ideas in the proposed approach to increase the degree of concurrency and to reduce the number of overhead messages in distributed simulation. >

Petri net based shop floor controller and recovery analysis

Abstract: The author develops a Petri-net-based shop-floor controller with a modular structure. This structure is made possible through the use of adaptive Petri nets. The controller is then analyzed using the theory of Petri nets. The issue of automatic recovery of the controller from failures is discussed. It is shown that in the presence of conflicts, the recovery scheme depends on the scheduling policies. >

Petri nets in dynamic process planning

Abstract: A framework for combining Petri Nets with Computer Aided Process Planning (CAPP) systems is presented. The Petri Nets are used to provide realtime facility status information while the CAPP system is used to generate the revised process plans. Combining these two methodologies overcomes most of the weaknesses with the traditional CAPP systems. The result is a dynamic, realtime CAPP system.

Design and verification of concurrent switching sequences with Petri nets

Abstract: The authors show how dynamical and structural properties of Petri nets can be used in proving important assertions about integrated control systems with the aid of computers. Methods of reducing complexity with Petri-net specifications are illustrated. To exploit analysis features, precise meanings must be given to the net entities, which leads to the choice of conditions/events (C/E) nets. Boundness is the first decidable property that allows proof of liveness and also the C/E nature for the nets. However, because this property demands an exponential algorithm, previous reduction must be done to preserve meaning. This preservation allows interpretation of the structural relations which can be proved for Petri nets. A tightly coupled set of automatic switching sequences is modeled and verified with Petri nets, specifying nontrivial bus and transformer operations in distribution substations. >

Some results on Petri net languages

Abstract: Various classes of Petri net languages are compared. A constructive proof of the equivalence, from the point of view of descriptive power of general Petri nets and restricted Petri nets (no multiple arcs of self-loops are allowed in the latter class), is presented. The descriptive power of Petri nets versus that of finitely recursive processes is discussed. >