The high level architecture

The High Level Architecture (HLA) provides a framework for building large-scale, distributed virtual worlds. HLA provides a standard approach for designing and implementing shared synthetic environments without restricting the developer to a particular programming language, computer architecture or operating system. It enables the developer to define and utilize any data content or format desired to communicate shared information between distributed simulations. HLA consists of three items: a set of rules for building and executing distributed simulations, an interface specification for the Run-Time Infrastructure (RTI) to provide certain services for data sharing and coordination between these simulations, and a standard Object Model Template (OMT) format for describing the data and interactions to be shared between these simulations. HLA was developed by a combined industry and government team in order to increase reusability and interoperability between heterogeneous simulations with diverse requirements. HIA is being proposed and considered as an industry standard architecture by the Institute of Electrical and Electronics Engineers, Inc. (IEEE) and has already been adopted by the Object Management Group (OMG) as the Facility for Distributed Simulation Systems and the United States Department of Defense (DoD) as a required standard for all DoD simulations. HLA is also being used in other countries and is being considered as a simulation standard internationally by the North Atlantic Treaty Organization (NATO). HLA is an architecture or a framework for building distributed simulations. As such, a virtual world (VW) developer is free to design and execute a particular implementation within the guidelines of the framework. The developer can use HLA with any programming language, any hardware platform, and any operating system running with any type of computer network. If an RTI does not yet exist for a given configuration, one can be written that conforms to the HIA interface specification. HLA, as an architecture, does not require the use of a particular RTI implementation nor does it limit the scope of a virtual world application. The software structure itself has no scalability issues; however limits may exist in a particular RTI implementation. Currlently, the only existing RTI implementation available is from the DoD; however, several US. and foreign companies are developing commercially available RTIs. The requirement for anyone developing an official RTI is that the complete HLA interface specification must be implemented (i.e., you cannot partially implement an official HLA RTI). The current RTI (and other HLA-related) software is available for download from the World Wide Web HLA home page (hla.dmso.mi1). The current DoD RTI (v1.3) implementation provides language bindings for C++, Ada95, Corba and Java and is available to support Solaris, IRE, AM, HP-UX, Windows NT and Linux operating systems. The Simulation Interoperability and Standards Organization, Inc. I:SISO) and the Defense Modeling and Simulation Office (DMSO) support email, electronic conferences and training programs for promoting HLA information interchange. Reality by Design (RBD) has been actively using the HLA to build VW applications for two years. Our efforts have involved developing cross-platform applications, most with entertainment potential. Using HLA on low-cost, commercial off-the-shelf (COTS) personal