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This paper is concerned with the analysis of the observability of the discrete event systems (DES) modeled by interpreted Petri nets (IPN). This paper presents three major contributions on the field of the observability of DES. First, an observability definition for IPN is proposed. This definition is more precise than previous ones because it deals with the possibility of determining the system's initial state, using the knowledge of the system's inputs, outputs, and structure. Later, a novel characterization of the IPN exhibiting the observability property that is based on the IPN structure is presented. Finally, a method for designing asymptotic observers is discussed. The main advantage over other methods is that the observer presented herein is given as an IPN, allowing further analysis of the system-observer pair. Index Terms--Discrete event systems (DES), observability, observers, Petri nets (PN).

Byline: Marina Flores-Badillo, Ernesto Lopez-Mellado, Mayra Padilla-Duarte A method for modelling complex workflow processes using a Petri Net (PN) based multilevel formalism is proposed; it yields modular and hierarchical descriptions of the organisation (or network of organisations), the processes, resource management and user interactions. The models allow the synthesis of agent based software in which mobile agents guide the cases through the organisation units; the software can be interactively executed for simulation purposes or distributed within a computer network for implementing a workflow management system. A tool for editing and simulating the models is presented.

The stability of discrete event systems (DESs) is a property related to its robustness; a stable DES is guaranteed to reach a set of desired states in a finite number of steps. Algorithms proposed in the literature are useful for analyzing the stability of DES modeled either by finite automata or a constrained subclass of Petri nets (PNs). In this paper, a novel method to decide the stability of safe PNs is presented. It is based on the analysis of the finite complete prefix of the net unfolding rather than the reachability graph. For concurrent systems, the prefix is usually smaller than the reachability graph and then the analysis using the proposed algorithm is more efficient than analyzing the reachability set of the PN. Note to Practitioners—The stability of a discrete event system (DES) is a property that guarantees that the DES will return to the normal operation behavior after a disturbance deviates the system from such a behavior. This is a key property that a controlled DES must fulfill. The algorithms proposed in this paper allow determining efficiently the stability of concurrent DES by analyzing the Petri net structure. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of discovering a Petri Net (PN) from a long event sequence representing the behavior of discrete-event processes. A method for building a 1-bounded PN able to execute the events sequence $S$ is presented; it is based on determining causality and concurrence relations between events and computing the t-invariants. This novel method determines the structure and the initial marking of an ordinary PN, which reproduces the behavior in $S$. The algorithms derived from the method are efficient and have been implemented and tested on numerous examples of diverse complexity. [ABSTRACT FROM AUTHOR]

This paper deals with the identification of discrete-event manufacturing systems that are automated using a programmable logic controller (PLC). The behavior of the closed-loop system (PLC and Plant) is observed during its operation and is represented by a single long sequence of observed input/output (I/O) signals vectors. The proposed method follows a black-box and passive identification approach that allows addressing large and complex industrial DES and yields compact and expressive interpreted Petri net (IPN) models. It consists of two complementary stages; the first one obtains, from the I/O sequence, the reactive part of the model composed by observable places and transitions. The I/O sequence is also mapped into a sequence of the created transitions, from which the second stage builds the non observable part of the model including places that ensure the reproduction of the observed input output sequence. This method, based on polynomial-time algorithms on the size of the input data, has been implemented as a software tool that generates and draws the IPN model; it has been tested with input/output sequences obtained from real systems in operation. The tool is described and its application is illustrated through a case study. [ABSTRACT FROM PUBLISHER]

This paper presents a modeling methodology for designing networked agents systems. It focuses on the agent hybrid state representation, its dynamic behavior, and its interaction with neighbor agents. The agent's internal state as well as the communication interface between agents is modeled using timed hybrid Petri nets. The methodology is illustrated through the modeling of a case study related to energy interchange networks. The simulation of the case study model is included to illustrate the advantages the proposed methodology. [ABSTRACT FROM AUTHOR]

This paper deals with diagnosis of permanent and operational faults of partially observed discrete event systems modeled by interpreted Petri nets capturing both normal and faulty behaviors. Two main results are presented: a structural characterization of the diagnosability property and a method for designing reduced model diagnosers for online fault detection and location. Sufficient conditions for diagnosability are provided based on the analysis of the influence area of every fault fi in the model and the relative distance between pairs of transitions; polynomial algorithms are proposed for determining diagnosability. The diagnoser includes two reduced models that monitor the system; one for tracking the actual behavior and the other for establishing the expected behavior; the difference of markings in such models, called residue, provides enough information for the immediate location of faults, even if they occur simultaneously. [ABSTRACT FROM PUBLISHER]

This paper deals with distributed creation and maintaining of ad hoc networks including diverse wireless devices, namely sensors, PDA, cell phones, and video games consoles. A cluster-based self-organizing strategy is proposed for building a backbone among the mobile devices, detecting segmentation, and recovery. In this approach, each mobile device is controlled by a multi-role agent, which performs these tasks efficiently based only on local interactions; role management allows the backbone reconfiguration when the nodes leave or arrive to the network yielding a complex global emergent behavior. Energy saving is achieved by adapting the time interval and power of transmission after the network formation. Simulations showed that the distributed algorithms performance is close to that obtained by an optimizing global procedure. [ABSTRACT FROM PUBLISHER]