ABSTRACT: The HLA Federation Object Model (FOM) describes the information that is to be exchanged during the execution of a federation. In earlier versions of HLA a federation had one monolithic FOM. HLA Evolved (the next version of HLA) introduces Modular FOMs which allow a federation to load FOM data as modules and to extend the FOM during the execution.
The modular approach to FOMs introduces many new opportunities and use cases:
Modular development of reference FOMs. Reference FOMs are very important for the reuse of federates. One example is the multitude of COTS and project specific RPR FOM based federates. They enable commercial and government users of M&S to quickly compose federations to meet their needs with low risk and at a modest cost. At the same time the sheer size of such FOMs, that may cover many aspects of the simulation, makes the development slow and costly. Modular FOMs can make this process quicker, more flexible and less costly.
Efficient handling of specialized extensions of reference FOMs. Reference FOMs are frequently modified and extended to support the simulation of local or specialized entities or services. This has resulted in a large number of uncorrelated versions of reference FOMs. As M&S users need to interoperate between sites, services and nations the handling of these non-standard versions of reference FOMs introduces risk and cost. Modular FOMs can separate out particular concerns thus preserving the reusability through reference FOMs and keeping the extension process
well-controlled.
Reusable federation agreements modules. For particular aspects of a federation, it will now be possible to provide a FOM module and a corresponding federation agreement. This may be a smaller aspect, like start and stop signaling or time pacing, or larger aspects like voice communications or weather services. In this way modular FOMs can support reuse of components of simulations systems across and between federations.
Support for long-running, GIG-style federations. Today’s HLA federations require the entire FOM to be loaded upon startup. In many larger systems, new capabilities need to be added over time without shutting down the entire federation. Modular FOMs allow new capabilities to be loaded when federates supporting these new capabilities join at a later point in time.
Authors: Björn Möller, Björn Löfstrand
Publication: Proceedings of 2007 Euro Simulation Interoperability Workshop, 07E-SIW-040, Simulation Interoperability Standards Organization, June 2007.