Title: Fault Diagnosis Graph of Time Petri Nets

Talk given by Xu Wang.

Abstract: A Discrete Event System (DES) is a dynamic system that evolves in accordance with the abrupt occurrence of events. Faults correspond to discrete events modeling abnormal behaviors and diagnosis is the process to detect faults. In a manufacturing system, a fault may be the failure of a certain operation, e.g., a wrong assembly, or a part put in a wrong buffer. In order to ensure the correct and safe function of large systems, fault diagnosis has attracted a significant attention in DES, untimed and timed systems. The increasing of complexity of systems makes the efficiency of fault diagnosis to be critical. In this work, an online approach for fault diagnosis of timed DES modeled by time Petri net is presented. In the net system, the firings of some transitions are not observable, while others are observable. The occurrence of observable transitions is always observable by an external observer while the occurrence of unobservable ones is not. Faults correspond to a subset of unobservable transitions. In accordance to most of the literature on DES, three diagnosis states, namely normal, faulty and uncertain states, are defined. The proposed approach uses a fault diagnosis graph, which is adapted from state class graph by keeping only the necessary information for computation of the diagnosis states and removing the unnecessary states. Algorithms to compute after each observation only the part of the fault diagnosis graph required to update the diagnosis states are given.

Title: Complexity Analysis of Continuous Petri Nets.

Talk given by Estíbaliz Fraca.

Abstract: Continuous Petri nets were introduced to avoid the state explosion problem of discrete Petri nets. Since then several works have established that the computational complexity of deciding some standard behavioural properties of Petri nets is reduced in this framework. Here we first establish the decidability of additional properties like boundedness and reachability set inclusion. We also design new decision procedures for the reachability and lim-reachability problems with a better computational complexity. Finally we provide lower bounds characterising the exact complexity class of the boundedness, the reachability, the deadlock freeness and the liveness problems.
This work is about continuous Petri nets, but it focus in decidability and complexity analysis, from theoretical computer science.