Showing papers on "Process architecture published in 1988"

Petri nets and flexible manufacturing

Abstract: The aim of this invited survey is to introduce Computer science/Petri nets specialists to the basic system level issues brought up by the development of Flexible Manufacturing and how Petri nets are used to aid the production engineers in their work. After some terminology concerning production engineering, the hierarchical decision and control level is briefly reviewed. Finally, the role and the presence of nets in CAE (Computer Aided Engineering) and in CAM (Computer Aided Manufacturing) for FMSs (Flexible Manufacturing Systems) are considered. From the design point of view, the use of nets have many advantages in modeling, qualitative analysis, performance evaluation and code generation. From the control of the plant perspective, scheduling on nets models, the coordination of the plant (global and partial) and the presence of nets in the local control level are discussed.

Nonsequential Processes: A Petri Net View

Abstract: The theory of the processes of concurrent systems is studied using partiallyordered sets The study is based on Petri net theory General properties of posets and their relations with properties of concurrent systems are examined

Stochastic high-level Petri nets and applications

Abstract: A class of stochastic Petri nets called stochastic high-level Petri nets (SHLPNs) is proposed. SHLPNs are high-level Petri nets augmented with exponentially distributed firing times. SHLPNs generally lead to models with a smaller state space. A computer marking concept is introduced that allows a considerable reduction of the number of states and induces a correct grouping of states in the Markov-domain SHLPN models of multiprocessor systems. The main advantage of modeling homogeneous systems using SHLPNs is that the resulting models are simpler and more intuitive and have a smaller number of states, as shown by examples. >

Petri nets are monoids: a new algebraic foundation for net theory

Abstract: The composition and extraction mechanisms of Petri nets are at present inadequate. This problem is solved by viewing place/transition Petri nets as ordinary, directed graphs equipped with two algebraic operations corresponding to parallel and sequential composition of transitions. A distributive law between the two operations captures a basic fact about concurrency. Novel 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. It is briefly indicated how the approach yields function spaces and novel interpretations of duality and invariants. The results provide a formal basis for expressing the semantics of concurrent languages in terms of Petri nets and an understanding of concurrency in terms of algebraic structures over graphs and categories that should apply to other models and contribute to the conceptual unification of concurrency. >

On Representing CCS Programs by Finite Petri Nets

Abstract: A non-interleaving semantics for a subset of CCS using finite place/transition-systems is presented. Straightforward constructions on nets for CCS operations are given. When restricting the language appropriately (no restriction and relabelling, only guarded choice), these operations yield a net semantics with a clear distinction of concurrency and nondeterminism. It is shown that the usual interleaving semantics is retrievable from the net semantics. Partial order semantics and equivalence notions for labelled P/T-systems are discussed. This shows how the intuitive causal dependencies in a CCS program are represented via the net semantics.

The use of Petri nets to analyze coherent fault trees

Abstract: The use of Petri nets to represent fault trees is discussed. Using reachability and other analytic properties of Petri nets, a more general and useful method to study the dynamic behavior of the model at various levels of abstraction is examined. The problems of fault-detection and propagation are discussed. For simplicity, only coherent fault trees are considered. However, the representation and analysis techniques are general and can be used for noncoherent fault trees. >

On the implementation of Petri nets

Abstract: In order to compare different distributed software implementations of the token game we start out from an explicitly defined basis, called the process paradigm. Quality criteria for implementations are specified and a variety of implementations of finite place/transition systems is discussed. The programs are formulated in Occam.

Extending Petri nets for specifying man-machine dialogues

Abstract: The requirements of man-machine dialogue-specification techniques are examined. Petri nets are identified as possible candidates for a modelling technique for dialogues on the basis of their applicability to concurrent, asynchronous systems. Labelled Petri nets are extended to nested Petri nets, allowing transitions to invoke subnets. It is shown that this extension allows nested Petri nets to generate at least the set of context-free languages. Further extensions are made to simplify the modelling of input and output in the user interface, resulting in input-output nets. Transitions labelled by error conditions and meta functions on nets are introduced to increase the usability of the model. Finally, the use of the model is demonstrated by modelling a small hypothetical command language.

OBJSA nets: a class of high-level nets having objects as domains

Abstract: To define classes of high level nets having structured (individual) tokens is a very fundamental goal for making nets actually usable in real concurrent system modelling. A promising approach is that of combining nets with algebraic specification techniques. This results in a formal specification language which supports both aspects of system modelling, namely data structure and control structure modelling, with suitable abstraction notions.

On the theory of intelligent machines: a survey

Abstract: Work aimed at formulating analytically the theory of intelligent machines is summarized. The functions of an intelligent machine are executed by intelligent controls. The principle of increasing precision with decreasing intelligence is used to form a hierarchical structure of the control systems. Distributed intelligence is compatible with such a structure when it is used for teams of intelligent machines or cooperating coordinators within the machine. The three levels of the intelligent control, i.e. the organization, coordination, and execution levels, are described as originally conceived. Designs such as neural nets for the organization level and Petri nets for the coordination level are also proposed. Applications to intelligent robots for space exploration are considered. >

Modeling and analysis of the behavior of information systems

Abstract: 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. >

A category of labelled Petri nets and compositional proof system

Abstract: An attempt is made to cast labeled Petri nets and other models in an algebraic framework One aim is to utilize the framework of categorical l to cast labeled Petri nets and other models in an algebraic framework The other aim is to utilize the framework of categorical logic to systematize specification languages and the derivation of proof systems for parallel processes A category of labeled nets is presented, and its categorical constructions are used to establish a compositional proof system A category of properties of nets is used in forming the proof system >

Planning via heuristic search in a Petri net framework

Abstract: An artificial intelligence planning system's main components consist of a planner and a problem domain. The problem domain is the environment about which the planner reasons and on which it takes action. In the paper, a special type of extended input/output Petri net is defined and then used as the problem representation for a wide class of problem domains. A planning strategy is developed using results from the theory of heuristic search. In particular, using the developed Petri net framework and metric spaces, a class of heuristic functions that are both admissible and consistent for the A* algorithm is specified. The planning system architecture is discussed, and, as an illustration of the results, two simple planning problems are modeled and solved. >

ESPNET: expert-system-based simulator of Petri nets

Abstract: A Petri net is a modelling tool used in the design and analysis of systems. The expertsystem language OPS5 has a similar execution strategy to a Petri net model, and hence Petri nets may be simulated using the OPS5 language. ESPNET has been designed to be used in a rapid prototyping mode to allow users to quickly develop simulation models of the work flow through manufacturing systems. The system described takes a Petri net for its input, and then generates an OPS5 simulator as output. The simulation model developed may then be used to size flexible assembly systems and flexible manufacturing systems based on the system performance andresource utilisation data generated by the model.

A hierarchical modeling methodology for flexible manufacturing systems using extended Petri nets

Abstract: A theory of extended Petri nets is proposed to enable the modeling of flexible manufacturing systems in a more comprehensive manner. The theory considers both the flow of control and flow of information, resources and parts in a system. A methodology for hierarchically modeling manufacturing systems using extended Petri net techniques, to ensure a priori the desirable properties of system performance is presented. The approach is based on modular modeling. >

Weighted Basic Petri Nets

Abstract: Basic net systems are proposed as an infinitary Petri net model which is sufficiently restrictive to allow essentially the same theory as finite nets, yet also powerful enough to describe the basic semantics of many concepts of concurrent programming languages. Weighted basic net systems are obtained if widths are assigned to the places and lengths are assigned to the transitions of a basic system. Using this enriched model run-time quantities such as space and time bounds can be derived. A translation of deterministic Turing machines into basic net systems is given.

Timed Petri nets and their application to communication protocol specification

Abstract: A generalized timed Petri net representation is defined and several time Petri net models compared. By introducing a new way to include a time variable in the Petri net and the firing rules, the authors realized a new timed Petri net that includes the other two principal types of timed Petri nets. This new timed Petri net seems to take a more general form than other types of time Petri nets defined so far. Therefore, complex systems are expected to be modeled with it. The authors present a model to represent a timer in order to model real communication systems properly. An example is given in which the timed Petri net representation and the timer model are applied to a communication protocol. With the results provided, communication protocols involving timers and transmission errors can be modeled. >

Music description and processing by Petri nets

Abstract: Music description and processing require formal tools which are suitable for the representation of iteration, concurrency, ordering, hierarchy, causality, timing, synchrony, non-determinism. Petri Nets (PNs) are a tool which allows to describe and process musical objects within both analysis/composition and performing environments. In this paper we discuss the kind of extended PNs that we have defined and their capabilities in the music field, the PNs editors/executors that we have developed and some characterizing PNs structures with musical examples; then we outline the open problems we have recognized.

Programming a closely coupled multiprocessor system with high level Petri nets

Abstract: This paper describes the application of high level Petri nets to program closely coupled multiprocessor (CCMp) systems. To use CCMp systems efficiently a special language based on high level nets and Concurrent Pascal was developed which allows an easy transformation of net specifications into programs, thus preserving their modular structure. The language was expanded with common objects in order to program the access to shared data efficiently. The implementation of the language and especially the synchronization of the concurrent token players is discussed.

Synthesis rules for cyclic interactions among processes in concurrent systems

Abstract: Designing concurrent systems has been shown to be difficult due to state explosion problems. A synthesis technique using Petri nets is proposed to tackle the problem. A set of rules has been proposed to guide designers incrementally expanding Petri nets under design while maintaining the logical correctness. These rules cover the semantics of concurrency, exclusiveness, cyclicity, and interactions. >

A process model for data bases

Abstract: we present a process model for data bases, which integrates concepts of relation, process, integrity constraint, event and period. The model allows one to specify the synchronization of processes and the constraints due to consumption and production of data. In particular we present the formalization which is carried out with the Petri Nets. These are obtained by using refining primitives which keep the interpretation simple for designers. The aspects of verification and validation of the specification are also examined.

Control flow analysis of distributed computing system software using structured Petri net model

Abstract: The structure Petri net model is presented for the representation and analysis of the control structures of distributed computing system software (DCSS). The basic properties of the model and some analysis techniques using this model are also presented. Liveness, reachability, and other related problems and their complexity are investigated. The NP-completeness of the reachability problem of this model is demonstrated. Four subclasses of structured Petri nets are then identified, and within these subclasses more efficient analysis methods based on decompositions are developed. Several O( mod T mod and O( mod T mod )/sup 2/) algorithms for liveness and reachability analyses are presented. Since most of these algorithms can be performed efficiently and economically, it is feasible that they can be integrated as an analysis tool for supporting the DCSS development process. >

Extensions on performance evaluation techniques for concurrent systems

Abstract: The authors present a procedure for computing the cycle time of concurrent systems modeled by a restricted class of Petri nets, i.e. decision-free and safe persistent nets. The procedure is based on formulating the cycle time computation as a minimal cost-to-time ratio cycle problem. The result is an efficient algorithm with a computational complexity of O(n/sup 3/log/sub 2/ n). By using an example with a stochastic counterpart, it is shown that the results are consistent with those obtained by more complex Markov analysis. >

A Petri net characterization of a high speed placement machine

Abstract: A high-speed placement machine for populating printed circuit boards with surface-mounted components is discussed. The operation of these machines requires the user to specify the setup of the workcell and the interrelated sequence of pick-and-place operations. These are complex process-control decisions which, unaided, require extensive engineering overhead. Their effective specification requires a thorough understanding of the machine's functional operations and also its control logic. Petri nets are used to provide a general framework to develop the characterization of this machine. It is shown that Petri nets provide a sufficiently flexible and yet formal framework in which to describe the concurrency, synchronization, and control of the operations which affect the throughput rate of the workcell. Thus an emulator can be derived and easily updated by coupling the Petri net representation with the MEGAS (Multiple Event Graph Analysis and Simulation) software package and the functional approximations used to model the characteristics of the motors and position servomechanisms. >

A specification language for real-time distributed systems

Abstract: The authors introduce a design specification method, extended modified Petri nets (EMPN), and its description language (EMPNDL). The specification is based on a stochastic Petri-net model and is suitable for modeling real-time distributed systems. The syntax of the language is formally described in BNF grammar while the semantics is based on that for stochastic Petric nets. In addition to the modeling capability of EMPN and EMPNDL, methods for verification and validation of such systems are also discussed. EMPN and EMPNDL have been extensively used to the specification of a prototype switching system, UICPBX. Based on the presented formulation, verification and validation of UICPBX can be automated to a great extent. >

Structural analysis of t-invariance of petri nets

Abstract: This paper studies the t-invariance of a Petri net by introducing two concepts of the rigidity for its existence and the marked-graph-reducibility for its efficient computation. Some characteristics and composition rules of rigidly connected Petri nets are given and an algorithm is designed to determine efficiently t-invariants of a marked-graph-reducible Petri net.

A method for the support of specifying the requirements of telecommunication systems

Abstract: The analysis of the functional behavior of telecommunication systems and its representation in a form that is largely independent of the implementation are described. A specification method for distributed systems has been devised that takes into account the special requirements of the first phases of the system lifecycle and the complexity of real systems. The method is based on the principles of essential systems analysis and uses a description based on a class of higher Petri nets specially defined for this purpose. The application of the proposed method allows a formal description of the functional behavior that can be structured at different abstraction levels. Computer tools are used to investigate the dynamic system behavior at each abstraction level by symbolic execution of the specification. >