Distributed heterogeneous simulations pose many problems for representations of a temporally and spatially consistent synthetic natural environment (SNE), especially if that environment is dynamic. The generation and distribution of the SNE in the run time formats of the simulation applications is one hurdle that must be overcome. In a dynamic environment, this data must be updated in an efficient, consistent manor as the exercise is taking place. Parallel Discrete Event Simulations (PDES), such as JSIMS, pose additional problems for a dynamic SNE. For instance, optimistic approaches may require that changes made to the simulation environment be "rolled back" if a simulation entity needs to revert to a time previous to the change. Changes to the SNE may require large amounts of data and processing time, so this requirement has serious run time implications. Also, each simulation entity may require a different view of the environment, depending on its location and notion of simulation time.

Under the DARPA Advanced Simulation Technology Thrust program, the Framework of Reusable Objects for the Synthetic Natural Environment (FROST) project is working to identify and address these issues, in order to provide a dynamic SNE representation that could be used in a distributed PDES simulation, such as JSIMS. The FROST approach is to develop a ground truth environment management system that uses PDES events for database updates, along with a commercial object oriented database management system. This paper will describe the issues associated with a distributed SNE in a PDES environment, how our approach addresses these issues, and our design efforts to date.