Collaborative modeling: The missing piece of distributed simulation

Teams of modelers brought together from different organizations generally have relied on ad hoc means to develop models. To achieve the coordination required in such collaboration, such teams rely on face to face discussions of issues, exchange their models via post or email and regularly consult through phone calls and teleconferences. The difficulties and expense involved in such coordination have often made building large-scale simulation models in a distributed manner cost prohibitive. Often, the difficulties involved are not recognized until too late, causing the project to be abandoned altogether. Under such circumstances, distributed modeling has not become a mainstream activity except for those who must rely on interoperability of models. For example, multinational corporations must depend on distributed modeling and simulation of the logistics supply and demand processes and therefore must overcome all barriers to collaboration of subject matter experts dispersed across space and time. The Department of Defense overarching goal of performing distributed simulation by overcoming geographic and time constraints has brought the problem of distributed modeling to the forefront. The High Level Architecture standard is primarily intended for simulation interoperability. However, as indicated, the existence of a distributed modeling infrastructure plays a fundamental and central role in supporting the development of distributed simulations. In this paper, we describe some fundamental distributed modeling concepts and their implications for constructing successful distributed simulations. In addition, we discuss the Collaborative DEVS Modeling environment that has been devised to enable graphically dispersed modelers to collaborate and synthesize modular and hierarchical models. We provide an actual example of the use of Collaborative DEVS Modeler (CDM) in application to a project involving corporate partners developing an HLA-compliant distributed simulation exercise.