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Iterative deadlock prevention strategies based on siphons have drawn increasing attention. For iterative strategies, selecting which siphon to control at each iteration has an influence on the final supervisor in structural complexity, computational complexity, and behavioral permissiveness. In this paper, we define two kinds of emptiable siphons and provide two modified mixed-integer programming (MIP) formulations to compute such siphons. On the basis of them, a three-stage iterative deadlock prevention policy that specifies the siphon control order is proposed. The experimental results show that a supervisor with a simpler structure, higher behavioral permissiveness, and lower computational complexity can be obtained by the proposed strategy since neither the exhaustive siphon enumeration nor the reachability analysis is required. INDEX TERMS Deadlock prevention, discrete event systems, mixed integer programming, Petri nets.

A cyber-physical system (CPS) typically consists of the plant, sensors, actuators, the controller and a communication network. The communication network connects the individual components to achieve the computing and communication in the CPS. It also makes the CPS vulnerable to network attacks. How to deal with the network attacks in CPSs has become a research hotspot. This paper surveys the types of network attacks in CPSs, the intrusion detection methods and the attack defense strategies. The future research directions of CPSs network security are also presented.INDEX TERMS Cyber-physical systems, network attacks, intrusion detection, defense strategies.

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