Trellis Processes : A Compact Representation for Runs of Concurrent Systems

The unfolding of a concurrent system represents in a compact manner all possible runs of this system. Unfoldings are used in many applications, ranging from model-checking (offline) to failure diagnosis (on-line). Their factorization properties form the basis of modular/distributed algorithms to achieve these tasks. The trellis structure proposed here is an alternate and more compact representation for the trajectory set of a concurrent system. In this structure, time is unfolded, but not the conflict relations. Trellis nets are the generalization to concurrent systems of the usual notion of trellis for an automaton. As for unfoldings, factorization properties are evidenced on trellises, which makes these more compact structures a possible candidate for distributed model checking or diagnosis algorithms. As an example, we show how trellises can be used for diagnosis purposes in a distributed observation setting.