Editing High Level Architecture (section)

== History and versions ==
HLA was initiated in the early 1990s when Dr. [[Anita K. Jones]], the Director of Defense Research and Engineering within the US Department of Defense, gave the [[Defense Modeling and Simulation Office]] (DMSO) the task of “assuring interoperability and reusability of defense models and simulations”.<ref name="Kuhl" /> In 1995 DMSO formulated a vision for modeling and simulation and established a modeling and simulation masterplan, which included the High Level Architecture.

Two protocols for M&S interoperability already existed: [[Distributed Interactive Simulation]] (DIS), focusing on real-time platform level simulation with a fixed object model, and [[Aggregate Level Simulation Protocol]] (ALSP) focusing on simulation of aggregate with time management, ownership management and flexible object models, called confederation models. The purpose of HLA was to provide one unified standard that would meet the simulation interoperability requirements of all US DoD components.<ref name="Dahmann1997" />

The development of HLA was based on four prototypical federations: the Platform Prototype Federation, the Joint Training Protofederation, the Analysis Protofederation and the Engineering Prototype Federation. The HLA specification was prototyped and refined, until HLA 1.3 was finally released. To facilitate usage outside of the defense community, HLA was then transitioned into an IEEE standard, maintained by [[Simulation Interoperability Standards Organization]] (SISO). To facilitate the migration for DIS users, a Federation Object Model corresponding to the fixed object model of DIS was also developed as the Real-time Platform Reference FOM ([[RPR FOM]]).

The following HLA versions exist:

=== HLA 1.3 ===
HLA 1.3 was published in March 1998 by DMSO. It consists of:  
* U.S. Department of Defense, Rules Version 1.3
* U.S. Department of Defense, High Level Architecture Interface Specification Version 1.3
* U.S. Department of Defense, High Level Architecture Object Model Template Version 1.3

The US DoD also published interpretations for HLA 1.3:
* U.S. Department of Defense, Interpretations of the High Level Architecture Interface Specification Version 1.3, Release 3

=== HLA 1516-2000 ===
HLA IEEE 1516-2000 was published in 2000 by IEEE. It consists of:
* IEEE Std 1516–2000 – Standard for Modeling and Simulation High Level Architecture – Framework and Rules
* IEEE Std 1516.1–2000 – Standard for Modeling and Simulation High Level Architecture – Federate Interface Specification
* IEEE 1516.1–2000 Errata (2003-oct-16)
* IEEE 1516.2-2000 – Standard for Modeling and Simulation High Level Architecture – Object Model Template (OMT) Specification

Major improvements in IEEE 1516-2000 included an XML-based FOM with detailed data type specifications, as well as an improved DDM design.

The IEEE 1516-2000 standard was also complemented by a recommended development process as well as a recommended VV&A process:
* IEEE 1516.3-2003 – Recommended Practice for High Level Architecture Federation Development and Execution Process (FEDEP). This standard would later become IEEE Std 1730-2010 Distributed Simulation Engineering and Execution Process ([[DSEEP]])
* IEEE 1516.4-2007 – Recommended Practice for Verification, Validation, and Accreditation of a Federation an Overlay to the High Level Architecture Federation Development and Execution Process

It was soon found that the 1516-2000 standard had APIs that were slightly different for each RTI implementation. SISO produced a standard with alternate, dynamic link compatible (DLC) C++ and Java APIs:

* SISO-STD-004.1-2004: Standard for Dynamic Link Compatible HLA API Standard for the HLA Interface Specification (IEEE 1516.1 Version)
* SISO-STD-004-2004: Standard for Dynamic Link Compatible HLA API Standard for the HLA Interface Specification (v1.3)

The DLC APIs were later merged into the main standard.

=== HLA 1516-2010 (HLA Evolved) ===
The IEEE 1516-2010 standard was published in August 2010 by IEEE and is commonly known as HLA Evolved.<ref>{{cite journal |last1=Möller |first1=Björn |last2=Morse |first2=Kathrine L |last3=Lightner |first3=Mike |last4=Little |first4=Reed |last5=Lutz |first5=Bob |title=HLA Evolved – A Summary of Major Technical Improvements  |journal=Proceedings of 2008 Spring Simulation Interoperability Workshop |date=April 2008 |url=https://www.sisostds.org/DigitalLibrary.aspx?Command=Core_Download&EntryId=28365}}</ref> It consists of:
* IEEE 1516–2010 – Standard for Modeling and Simulation High Level Architecture – Framework and Rules<ref name="RULES" />
* IEEE 1516.1–2010 – Standard for Modeling and Simulation High Level Architecture – Federate Interface Specification<ref name="IFSPEC" />
* IEEE 1516.2-2010 – Standard for Modeling and Simulation High Level Architecture – Object Model Template (OMT) Specification<ref name="OMTSPEC" />

Major improvements in IEEE 1516-2010 include Modular FOMs,<ref>{{cite journal |last1=Möller |first1=Björn |last2=Löfstrand |first2=Björn  |title=Getting started with FOM Modules 
 |journal=Proceedings of 2009 Fall Simulation Interoperability Workshop |date=September 2009 |url=https://www.sisostds.org/DigitalLibrary.aspx?Command=Core_Download&EntryId=28770}}</ref> incorporation of the DLC APIs in C++ and Java, a Web Services API<ref>{{cite journal |last1=Möller |first1=Björn |last2=Löf |first2=Staffan  |title=A Management Overview of the HLA Evolved Web Service API   |journal=Proceedings of 2006 Fall Simulation Interoperability Workshop |date=September 2006 |url=https://www.sisostds.org/DigitalLibrary.aspx?Command=Core_Download&EntryId=27092}}</ref> and Fault Tolerance.<ref>{{cite journal |last1=Möller |first1=Björn |last2=Karlsson |first2=Mikael |last3=Löfstrand |first3=Björn |title=Developing Fault Tolerant Federations using HLA Evolved  |journal=Proceedings of 2005 Spring Simulation Interoperability Workshop |date=April 2005 |url=https://www.sisostds.org/DigitalLibrary.aspx?Command=Core_Download&EntryId=26664}}</ref>

Machine-readable parts of this version of HLA, such as XML Schemas, C++, Java and [[Web Services Description Language|WSDL]] APIs as well as FOM/SOM samples can be downloaded from [https://standards.ieee.org/downloads/ the IEEE 1516 download area of the IEEE web site]. The full standards texts are available at no cost to SISO members or can be purchased from [https://web.archive.org/web/20001206215800/http://www.shop.ieee.org/ the IEEE shop].

=== HLA 1516-2025 (HLA 4) ===
The development of a new version of HLA started in January 2016 by SISO and is currently ongoing. 

On April 22nd 2024 the HLA 4 has been approved in its first round of IEEE balloting. <ref>https://pitchtechnologies.com/2023/05/hla-4-approved-in-ieee-balloting/</ref>

During the 2025 Simulation Innovation Workshop (SIW) the HLA 4 was approved by IEEE. The preliminary publication date is set for late March or early April of 2025. HLA 4 offers improved security, scalability, extensibility, cloud and container readiness, and full life-cycle support. <ref>https://www.sisostandards.org/news/695782/HLA-4-Approved-by-IEEE.htm</ref>