RPR FOM

The Real-time Platform Reference Federation Object Model (RPR FOM) enables linking computer simulations of discrete physical entities into complex virtual worlds. It is a High Level Architecture (HLA) federation object model developed for distributed simulation applications of defense and security. RPR FOM is listed in the NATO Modelling and Simulation Standards Profile AMSP-01.
The RPR FOM provides backwards compatibility with simulations using the Distributed Interactive Simulation (DIS) standard. It is standardized by Simulation Interoperability Standards Organization (SISO) as SISO-STD-001-2015.
The standard consists of two parts: 
History and versions.
When the High Level Architecture was introduced by the US Department of Defense in 1996 the RPR FOM effort was initiated to facilitate the migration from DIS to HLA.
RPR FOM version 1.0.
This first RPR FOM version was released in 1998. It supports the capabilities of DIS version IEEE 1278.1-1995 (DIS 5). The standard provides a FOM supporting HLA version 1.3.
RPR FOM version 2.0.
This updated version was released in 2015 as SISO-STD-001. RPR FOM 2.0 supports the capabilities of DIS version IEEE 1278.1a-1998 (DIS 6). The development of RPR FOM 2.0 started in 2000, but came to a halt in 2007, resulting in a widely used draft version 17. The work was restarted in 2012 and finalized with a published standard in 2015. The standard provides FOMs supporting the following HLA versions: 1.3, IEEE 1516-2000 and IEEE 1516-2010 (“HLA Evolved”) in both modular and monolithic formats.
RPR FOM version 3.0.
Development of this upcoming version was started in 2016 by the SISO DIS and RPR FOM Product Support Group. In 2018, the development was handed over to a dedicated Product Development Group. The goal of RPR FOM version 3.0 is to support the capabilities of DIS version IEEE 1278.1-2012 (DIS 7).
Object model.
The RPR FOM defines the information exchanged at runtime in a number of FOM modules:
Additional supporting modules include Foundation Module with a few basic data types, Enumerations Module with enumerations like types of platforms and equipment, Base Module with commonly used data types and generic object classes and Switches Module with runtime switches for the RTI.
Relationship to other standards.
The RPR FOM is related to a number of other standards.