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Top1. Introduction
With the rapid development of computing technologies, modeling and simulation (M&S) has become an integral part of the modern research and development process (Günal & Pidd, 2011; Stopford & Counsell, 2008). A common representation of the physical environment is a critical element in M&S and is a necessary precondition for the interoperability of heterogeneous simulations (Sedris, 1994). Recently, integration of heterogeneous simulations increases to work together with different simulations. Especially, in the defense industry, integration of simulations is widely used. For example, flight simulations for training several pilots and a simulation for command-level training where officers are trained to manage complex situations and command thousands of simulated participants can be integrated (Moller, 2012). Interoperability of heterogeneous simulations depends heavily on sharing complex environmental data in a consistent and complete manner (Ryu, 2009).
The environmental data of distributed simulations is managed by a separate environmental data server that is connected in a network. The environmental data server stores the environmental data before other simulations are conducted, and the environmental data in the environmental data server is not changed after the data is stored. The stored data is utilized as the reference data of a specific environmental condition. A simulation in a network sends a request to the environmental data server in order to get some environmental data of a specific location with a specific condition. Between the environmental data server and other simulations, the fast data retrieval is essential. If the data retrieval is not fast enough, receiving the environmental data can become a bottleneck of simulations. Thus, for the environmental data server, the performance of the storing side is not important as compared with that of the retrieval side.
The Synthetic Environmental Data Representation and Interchange Specification (SEDRIS) is an ISO standard for representation and interchange of environmental data such as ocean, terrain, atmosphere, and space, etc. SEDRIS is based on five core technology components which are the SEDRIS Data Representation Model (DRM), the Environmental Data Coding Specification (EDCS), the Spatial Reference Model (SRM), the SEDRIS interface specification (SEDRIS API), and the SEDRIS Transmittal Format (STF). The DRM, the EDCS, and the SRM are used to achieve an unambiguous representation of environmental data. The SEDRIS API and the STF allow an efficient sharing and interchange of the environmental data represented by the other three components.