Robustness of Time Petri Nets under Guard Enlargement
Abstract
Robustness of timed systems aims at studying whether infinitesimal perturbations in
clock values can result in new discrete behaviors. A model is robust if the set of discrete behav-
iors is preserved under arbitrarily small (but positive) perturbations. We tackle this problem for time
Petri nets (TPNs, for short) by considering the model of parametric guard enlargement which allows
time-intervals constraining the firing of transitions in TPNs to be enlarged by a (positive) parameter.
We show that TPNs are not robust in general and checking if they are robust with respect to standard
properties (such as boundedness, safety) is undecidable. We then extend the marking class timed
automaton construction for TPNs to a parametric setting, and prove that it is compatible with guard
enlargements. We apply this result to the (undecidable) class of TPNs which are robustly bounded
(i.e., whose finite set of reachable markings remains finite under infinitesimal perturbations): we
provide two decidable robustly bounded subclasses, and show that one can effectively build a timed
automaton which is timed bisimilar even in presence of perturbations. This allows us to apply
existing results for timed automata to these TPNs and show further robustness properties.
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