Synthesis of Reduced Asymmetric Choice Petri Nets

Abstract

A Petri net is choice-free if any place has at most one transition in its postset (consuming its tokens) and it is (extended) free-choice (EFC) if the postsets of any two places are either equal or disjoint. Asymmetric choice (AC) extends EFC such that two places may also have postsets where one is contained in the other. In reduced AC nets this containment is limited: If the postsets are neither disjoint nor equal, one is a singleton and the other has exactly two transitions. The aim of Petri net synthesis is to find an unlabelled Petri net in some target class with a reachability graph isomorphic to a given finite labelled transition system (lts). Choice-free nets have strong properties, allowing to often easily detect when synthesis will fail or at least to quicken the synthesis. With EFC as the target class, only few properties can be checked ahead and there seem to be no short cuts lowering the complexity of the synthesis (compared to arbitrary Petri nets). For AC nets no synthesis procedure is known at all. We show here how synthesis to a superclass of reduced AC nets (not containing the full AC net class) can be done.