An environmental data model (EDM) explicitly captures the phenomena (e.g., features) in the natural environment, the qualifying attributes of those phenomena, and the implicit relationships among phenomena. As such, the environmental data model is a key element of a simulation system - at the program specific level, it describes the geospatial environment in which the simulation takes place and with which all entities interact. These interactions serve as a compelling reason to establish the program environmental data model early in the development process, i.e., during system requirements analysis. In practice, it is best to define the data model as one of the first requirements analysis activities due to its broad impact throughout the overall system. Important system elements affected are the behavioral and dynamic models and hence the overall effectiveness of the system in providing the required capabilities, be they training, analysis, or acquisition based. Historically, requirements analysis has involved analysis of a system's intended operational use and the entities to be modeled. Complex systems might characterize hundreds of unique enitity types. Ideally, all entities to be modeled will have a consistent representation of the world. The ability to achieve this is facilitated by the EDM. Additionally, system development efforts will be better focused if the program EDM is developed early in the system lifecycle.

Until recently, environmental data modeling has been ad hoc, with the data models captured only in implicit fashions such as in source code or data files, if at all. The Army Warfighter Simulation (WARSIM) 2000, a component of the Joint Simulation System (JSIMS), defined a Terrain Common Data Model (TCDM) for use throughout the JSIMS Alliance. The Army Synthetic Natural Environment (SNE) Science and Technology Objective (STO) has developed a Common Data Model Framework (CDMF) to promote the comparison of program specific EDMs and support the higher resolution requirements of the OneSAF Test Bed and the Close Combat Tactical Trainer (CCTT). The Reference EDM which will ultimately result from the unification of these program-specific EDMs will provide an important infrastructure for achieving environmental interoperability within the community of land combat simulations. Additionally, the SNE STO is addressing critical system-of-systems interoperability issues by developing explicit data modeling technology to support the concept of representing environmental phenomena at multiple levels of resolution. In a related activity, the Defense Modeling and Simulation Office (DMSO) is extending the CDMF concept from terrain to the ocean and atmosphere domains. Creating these EDMs for Ocean and for Atmosphere supports the overall goal of establishing a general Environmental Data Model composed of environmental sub-domain EDMs (terrain, ocean, atmosphere and space) from which user community Reference EDMs and program specific EDMs would be generated as profiles.

This paper provides an overview of the environmental data models developed to date, focusing on the importance of developing such a model early in the simulation system development process. The general process for developing such a data model is also described.