High Level Architecture - AbsoluteAstronomy.com

A high-level architecture (HLA) is a general purpose architecture for distributed computer simulation

Computer simulation

A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...

systems. Using HLA, computer simulations can interact (that is, to communicate data, and to synchronize actions) to other computer simulations regardless of the computing platforms. The interaction between simulations is managed by a Run-Time Infrastructure (RTI).

Technical overview

A high-level architecture consists of the following components:

Interface specification, that defines how HLA compliant simulators interact with the Run-Time Infrastructure (RTI). The RTI provides a programming library
Library (computer science)
In computer science, a library is a collection of resources used to develop software. These may include pre-written code and subroutines, classes, values or type specifications....

and an application programming interface
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...

(API) compliant to the interface specification.
Object model template (OMT), that specifies what information is communicated between simulations, and how it is documented.
Rules, that simulations must obey in order to be compliant to the standard..

Common HLA terminology

Federate: an HLA compliant simulation entity.
Federation: multiple simulation entities connected via the RTI using a common OMT.
Object: a collection of related data sent between simulations.
Attribute: data field of an object.
Interaction: event sent between simulation entities.
Parameter: data field of an interaction.

Interface specification

The interface specification is object oriented. Many RTIs provide APIs in C++

C++

C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...

and the Java

Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...

programming languages.

The interface specification is divided into service groups:

federation management
declaration management
object management
ownership management
time management
data distribution management
support services

Object model template

The object model template (OMT) provides a common framework for the communication between HLA simulations. OMT consists of the following documents:

Federation object model (FOM). The FOM describes the shared object, attributes and interactions for the whole federation.
Simulation object model (SOM). A SOM describes the shared object, attributes and interactions used for a single federate.

HLA rules

The HLA rules describe the responsibilities of federations and the federates that join.

Federations shall have an HLA federation object model (FOM), documented in accordance with the HLA object model template (OMT).
In a federation, all representation of objects in the FOM shall be in the federates, not in the run-time infrastructure (RTI).
During a federation execution, all exchange of FOM data among federates shall occur via the RTI.
During a federation execution, federates shall interact with the run-time infrastructure (RTI) in accordance with the HLA interface specification.
During a federation execution, an attribute of an instance of an object shall be owned by only one federate at any given time.
Federates shall have an HLA simulation object model (SOM), documented in accordance with the HLA object model template (OMT).
Federates shall be able to update and/or reflect any attributes of objects in their SOM and send and/or receive SOM object interactions externally, as specified in their SOM.
Federates shall be able to transfer and/or accept ownership of an attribute dynamically during a federation execution, as specified in their SOM.
Federates shall be able to vary the conditions under which they provide updates of attributes of objects, as specified in their SOM.
Federates shall be able to manage local time in a way that will allow them to coordinate data exchange with other members of a federation.

Base Object Model

The Base Object Model (BOM) is a new concept created by SISO to provide better reuse and composability for HLA simulations, and is highly relevant for HLA developers. More information can be found at Boms.info.

Federation development and execution process (FEDEP)

FEDEP, IEEE 1516.3-2003, is a standardized and recommended process for developing interoperable HLA based federations. FEDEP is an overall framework overlay that can be used together with many other, commonly used development methodologies.

Distributed Simulation Engineering and Execution Process (DSEEP)

In spring 2007 SISO started revising the FEDEP. It has been renamed to Distributed Simulation Engineering and Execution Process (DSEEP) and is now an active standard IEEE 1730–2010 (instead of IEEE 1516.3).

Standards

HLA is defined under IEEE Standard 1516:

IEEE 1516–2010 – Standard for Modeling and Simulation High Level Architecture – Framework and Rules
IEEE 1516.1–2010 – Standard for Modeling and Simulation High Level Architecture – Federate Interface Specification
IEEE 1516.2-2010 – Standard for Modeling and Simulation High Level Architecture – Object Model Template (OMT) Specification
IEEE 1516.3-2003 – Recommended Practice for High Level Architecture Federation Development and Execution Process (FEDEP)
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

Machine-readable parts of the standard, such as XML Schemas, C++, Java and WSDL APIs as well as FOM/SOM samples can be downloaded from the IEEE 1516 download area of the IEEE web site. The full standards texts are available at no extra cost to SISO members or can be purchased from the IEEE shop.

Previous version:

IEEE 1516–2000 – Standard for Modeling and Simulation High Level Architecture – Framework and Rules
IEEE 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

STANAG 4603

HLA (in both the current IEEE 1516 version and its ancestor "1.3" version) is the subject of the NATO standardization agreement (STANAG 4603) for modeling and simulation: Modeling And Simulation Architecture Standards For Technical Interoperability: High Level Architecture (HLA).

DLC API

SISO has developed a complementary HLA API specification known as the Dynamic Link Compatible (DLC) API. The DLC API addresses a limitation of the IEEE 1516 and 1.3 API specification, whereby federate recompilation was necessary for each different RTI implementation. Note that this API has since been superseeded by the HLA Evolved APIs, informally known as Evolved DLC APIs (EDLC).

HLA Evolved

The IEEE 1516 standard has been revised under the SISO HLA-Evolved Product Development Group and was approved 25-Mar-2010 by the IEEE Standards Activities Board. The revised IEEE 1516–2010 standard includes current DoD standard interpretations and the EDLC API, an extended version of the SISO DLC API. Other major improvements include:

Extended XML support for FOM/SOM, such as Schemas and extensibility
Fault tolerance support services
Web Services (WSDL) support/API
Modular FOMs
Update rate reduction
Encoding helpers
Extended support for additional transportation (such as QoS, IPv6,...)
Standardized time representations

Alternatives

While no direct alternatives to HLA are known to exist Distributed Interactive Simulation

Distributed Interactive Simulation

Distributed Interactive Simulation is an IEEE standard for conducting real-time platform-level wargaming across multiple host computers and is used worldwide, especially by military organizations but also by other agencies such as those involved in space exploration and medicine.-History:The...

(DIS) is widely used for similar purposes. HLA was intended to succeed DIS as the interconnect fabric of choice for distributed Modeling and Simulation

Modeling and simulation

Modeling and simulation is the use of models, including emulators, prototypes, simulators, and stimulators, either statically or over time, to develop data as a basis for making managerial or technical decisions. The terms "modeling" and "simulation" are often used interchangeably.The use of...

(M&S) exercises. However, interoperation among HLA participants requires the use of the same RTI vendor software and in some RTI implementations the same RTI version. This lack of a network (wire) level standard often forces applications to use the older DIS protocol.

External Links

proto-x: a cross-platform, open source C++ library for developing HLA compliant simulations, tools, and utilities.
Portico: an open source, cross-platform HLA RTI implementation.

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