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Title:On computing a liveness enforcing supervisory policy for a class of general petri nets
Author(s):Somnath, Nisha
Director of Research:Sreenivas, Ramavarapu
Doctoral Committee Chair(s):Sreenivas, Ramavarapu
Doctoral Committee Member(s):Beck, Carolyn; Stipanovic, Dusan; Voulgaris, Petros
Department / Program:Industrial & Enterprise Systems Engineering
Discipline:Industrial Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Petri Nets
Supervisory control
Discrete event systems
Abstract:Discrete-Event/Discrete-State (DEDS) Systems are prone to livelocks. Once a system enters a livelocked-state, there is at least one activity of the modeled system that cannot be executed from all subsequent states of the system. This phenomenon is common to many operating systems where some process enters into a state of suspended animation for perpetuity, and the user is left with no other option than to terminate the process, or reboot the machine. This thesis is about computing Liveness Enforcing Supervisory Policies (LESPs) for Petri net (PN) models of DEDS systems. The existence of an LESP for general PNs is not even semi-decidable. This thesis identifies two classes of PNs F and H for which the existence of a LESP is decidable. It also describes an object-oriented implementation of a procedure for the synthesis of the minimally-restrictive LESP for any instance from these classes. The minimally-restrictive LESP prevents the occurrence of events in a DEDS system only when it is absolutely necessary. A suite of methods, based on refinement/abstraction concepts, is developed to reduce the complexity of LESP-synthesis. This involves the synthesis of a LESP for a simplified-version of a complex PN structure, which is subsequently refined to serve as a LESP for the original complex PN. Two PNs are in a simulation relationship if their behaviors are "similar" in a formal sense. The thesis concludes with a result that shows that the above mentioned procedure can be generalized to PNs in simulation relationships. That is, a LESP for a PN can be modified to serve as a LESP for another PN that is "similar". The implementation of this theoretical observation is suggested as a topic for future work.
Issue Date:2015-12-01
Rights Information:Copyright 2015 Nisha Somnath
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12

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