In this paper, we study the nonblocking supervisor synthesis problem in partially observed discrete event systems modeled by finite-state automata. We consider a particular type of supervisors that can observe not only the execution of observable events in a plant but also the quiescence of it. We first define a q-observer to characterize the behavior of a plant with observable quiescence. Comparing with the classical observer structure, the q-observer contains the quiescence information of a plant, which can be used to improve state estimation. Then we propose a method to detect the blocking states in a$q$-observer. Finally, we develop an iterative method to synthesize a nonblockingness enforcement supervisor from the$q$-observer. Since quiescence provides additional information on state estimation, the supervisor synthesized by the proposed method is in general more permissive than those synthesized by the existing approaches that do not monitor the quiescence. A manufacturing system example is also given to elucidate the effectiveness of the developed approachNote to Practitioners—A discrete event system is a discrete-state and event-driven system, covering a deluge of contemporary computer-integrated man-made constructs, such as automated manufacturing systems, smart urban transportation systems and computer communication networks. Such a system is in general partially observed due to the limited sensor deployment, which complicates its controller design. This research studies the typical supervisory control problem for a partially observed discrete event system. A supervisor is designed to restrict the dynamics of the system in order to guarantee a safe operation through a different control scheme by using the quiescence information that can be usually provided by a real-world system. The practitioners in control and automation community are capable of practicing the formulated control scheme for engineering applications.

This research focuses on the forbidden state problem in the framework of labeled Petri nets (LPNs), i.e., to design a supervisor for a plant modeled by an LPN such that the closed-loop system cannot reach a set of predefined forbidden markings and does not contain any deadlock. Different from the traditional control scheme, the supervisor derived by this work can not only observe the observable transitions, but also the quiescence information. First, a new structure named an extended basis reachability graph (EBRG) is introduced to describe the reachability space of an LPN without computing all reachable markings. Based on an EBRG, a basis observer is then excogitated to represent the behavior of an LPN. Some states in the basis observer are defined as bad states and control-induced deadlocks, which relates to the undesirable behavior of the plant. Finally, an algorithm is introduced to compute a supervisor based on the basis observer. The consideration of system quiescence provides extra information on the marking estimation of the closed-loop system such that certain disabled transitions are re-enabled. Consequently, the developed supervisor in this article is generally more permissive than those do not observe the quiescence.

Rumor spreads fast in social networks and may seriously damage our society. In this article, we present a mathematical programming formulation based on integer linear programming (ILP) to minimize rumor spread by blocking a subset of nodes (called blockers) in complex social networks modeled as a linear threshold model. We also propose a modified approach which solves the top-$k$blockers problem with a reduced computational effort and formally proves that its performance is still optimal. Then, the presented method is evaluated for its effectiveness of containing rumor spread in four different networks and its performance is compared with a greedy-based and two centrality-based approaches. The experimental analysis shows that the ILP-based method outperforms the other three approaches and is applicable to large-scale networks.

This article proposes a semi-structural approach to verify thenonblockingnessof a Petri net. We construct a structure, called minimal-maximal basis reachability graph (min-max-BRG): it provides an abstract description of the reachability set of a net while preserving all information needed to test if the net isblocking. We prove that a bounded deadlock-free Petri net isnonblockingif and only if its min-max-BRG isunobstructed, which can be verified by solving a set of integer constraints and then examining the min-max-BRG. For Petri nets that are not deadlock-free, one needs to determine the set of dead markings. This can be done with an approach based on the computation ofmaximal implicit firing sequencesenabled by the markings in the min-max-BRG. The approach we developed does not require the construction of the reachability graph and has wide applicability.

In this paper a type of specifications called OR-GMEC for place/transition nets is defined. Such a specification consists of a set of disjunctive Generalized Mutual Exclusion Constraint, i.e. the requirement is that, at any given time, the controlled system should satisfy at least one of them. We show that a bounded OR-GMEC can be enforced by a special control structure composed by a set of monitor places (one for each constraint) plus a switcher that determines the current active constraint. We also show that such a simple control structure is not maximally permissive, and characterize this problem identifying a special subset of transitions that may be over-restricted. A modified controller that ensures maximal permissiveness is also presented. Finally, we discuss a particular control problem, that consists in preventing the firing of a given set of transitions and show that it can be reduced to an OR-GMEC problem.