Control theory traditionally has been focused on analysis and control of continuous systems with numerical characteristics. In the past decade, however, there has been a growing concern with the symbolic aspect of systems owing to the advances in computer engineering. As a result the discipline of Discrete-Event Systems (DES) is emerging from the system control community.;In the framework of Ramadge and Wonham (RW), signals of interest no longer assume the form of continuously valued functions of numbers, but instead are discrete strings of symbols. The system is controlled by disablements of controllable events. In practice, RW control theory is found to be effective for systems of small size, but in the case of large systems, the computational complexity may become intractable.;This thesis proposes a generalization of the RW framework. Systems are modeled as multilevel hierarchies in which high-level dynamics are obtained via abstraction of the low-level models, and this vertical modularity approach leads to a significant reduction in the computational effort. Conditions on abstraction are established in order to enforce safety and liveness specifications at all levels of the hierarchy. Finally two case studies are presented to illustrate how the theory may be applied in practice.
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