Synthesis of Pure and Impure Petri nets With Restricted Place-environments: Complexity Issues (2112.03608v6)

Abstract: Petri net synthesis consists in deciding for a given transition system $A$ whether there exists a Petri net $N$ whose reachability graph is isomorphic to $A$. Several works examined the synthesis of Petri net subclasses that restrict, for every place $p$ of the net, the cardinality of its preset or of its postset or both in advance by small natural numbers $\varrho$ and $\kappa$, respectively, such as for example (weighted) marked graphs, (weighted) T-systems and choice-free nets. In this paper, we study the synthesis aiming at Petri nets which have such restricted place environments, from the viewpoint of classical and parameterized complexity: We first show that, for any fixed natural numbers $\varrho$ and $\kappa$, deciding whether for a given transition system $A$ there is a Petri net $N$ such that (1) its reachability graph is isomorphic to $A$ and (2) for every place $p$ of $N$ the preset of $p$ has at most $\varrho$ and the postset of $p$ has at most $\kappa$ elements is doable in polynomial time. Secondly, we introduce a modified version of the problem, namely Environment Restricted Synthesis (ERS, for short), where $\varrho$ and $\kappa$ are part of the input, and show that ERS is NP-complete, regardless whether the sought net is impure or pure. In case of the impure nets, our methods also imply that ERS parameterized by $\varrho+\kappa$ is $W[2]$-hard.