Hierarchical control of discrete-event systems

This paper is an overview of the current research on hierarchical control of discrete-event systems. Four major approaches are identified and described: bottom-up design, top-down design, state aggregation, and interface-based design. The research examined is grouped into these sections, in an attempt to unify the terminology and concepts where possible without an in-depth theoretical investigation. The motivation for this paper is to examine the different approaches to hierarchical control of discrete-event systems with an eye on their implications for the usability of the proposed models.