Crowd Federate Architecture and API Design Frederic(Rick) D. McKenzie Qingwen Xu Quynh-Anh H. Nguyen Mikel D. Petty Virginia Modeling, Analysis and Simulation Center Old Dominion University Norfolk, VA. 23529 757.683.5590, 757.683.6367 fmckenzi@ece.odu.edu, mpetty@odu.edu Keywords: Crowd behavior, API design, game technology ABSTRACT: Our United States military is increasingly engaged in urban combat or peace-keeping missions. As a result, soldiers are also increasingly engaged with the civilian non-combatant inhabitants of various nations. Yet, current military simulation models have little or no representation of these effects which can lead to suboptimal training or experimentation results. More realistic and sophisticated crowd models are desired to address this growing need. It is unlikely that one crowd model will meet all our military’s crowd requirements since models are needed with a variety of behaviors depending upon the type of mission, the size of encounters, and the user application. A federate that may be used to provide such variety of civilian behaviors in a crowd context would need to be flexible, configurable, and extensible. In this paper, we report about one such instantiation and the framework which supports it. The framework is a layered architecture that is composed of a physical layer in which movements and other actions of the crowd are manifested; and also a cognitive layer in which the motivations of these activities are generated and propagated. Connecting these two layers is an API layer that provides mapping and communication services for the stimuli, activities, and accompanying parameters that are crowd behavior centric. Included in the paper are details about the API and the design process used to achieve it. Also included is a description of the integration of game technology used to provide the physical layer portion for this particular instantiation of the crowd federate. 1. INTRODUCTION Crowds of non-combatants play a large and increasingly recognized role in modern military operations, and often create substantial difficulties for the combatant forces involved. “In Somalia, U. S. Marines often faced hostile crowds of rock-throwing women and children. In Bosnia, U. S. Army soldiers had to disperse angry mobs of Serb hard-liners near the town of Banja Luka. More recently, Danish, French, and Italian forces attempted to control riots between ethnic Albanians and Serbs in Mitrovice, Albania.” [1] “All military operations, large or small, have a crowd control/crowd confusion factor. … [C]rowds are one of the worst situations you can encounter. There is mass confusion; loss of control and communication with subordinates; potential for shooting innocent civilians, or being shot at by hostiles in the crowd; potential for an incident at the tactical level to influence operations and policy at the strategic level.” [2] In spite of the military challenges and risks imposed by crowds, models of crowds are essentially absent from current production military simulations. This omission has been understandable in the context of legacy simulations that were historically focused on large-scale engagements between heavy mechanized forces in primarily non-urban settings. However, in the last decade