Activity cycle diagrams (ACDs) have long been used for the representation of the flow of entities within discrete-event systems. They can be used to manually simulate systems and their description serves as the basis for automatically generating activity-based simulation code. Although activity-based approaches are cited as one of the easiest ways to model systems their proliferation has been hindered by concerns of efficiency, support, and flexibility. In this paper, these concerns are addressed as well as simulation methods that support the multi-layered ACDs to assist in overcoming these issues. 123-1 3 1. AUTHOR BIOGRAPHIES KURT A. PFLUGHOEFT is an Assistant Professor in the Information and Decision Sciences Department at the University of Texas at El Paso. He received his M.S. and Ph.D. degrees from the University of Wisconsin-Milwaukee in 1986 and 1993. He has worked as a systems analyst and computer consultant for numerous companies. His research interests include FMS design and scheduling, simulation, knowledge-based systems, information metrics, and object-oriented design principles. KIRAN MANUR is a graduate student in the Department of Manufacturing Engineering. He received his B.S. from Bangalore University in 1990. His thesis addresses the conversion of ACDs into an object-oriented representations. His other research interests include database and interface design.