Functional Mock-up Interface

<h2 id="the-fmi-approach">The FMI approach</h2>
<p>The typical FMI approach is described in the following stages:
</p>
<ul><li>a modelling environment describes a product sub-system by differential, algebraic and discrete equations with time, state and step-events. These models can be large for usage in off-line or on-line simulation or can be used in embedded control systems;</li>
<li>as an alternative, an engineering tool defines the controller code for controlling a vehicle system;</li>
<li>such tools generate and export the component in an FMU (Functional Mock-up Unit);</li>
<li>an FMU can then be imported in another environment to be executed;</li>
<li>several FMUs can – by this way – cooperate at runtime through a co-simulation environment, thanks to the FMI definitions of their interfaces.</li></ul>
<h2 id="license">License</h2>
<p>The <a href="https://www.fmi-standard.org/downloads">FMI specifications</a> are distributed under open source licenses:
</p>
<ul><li>the specifications are licensed under CC BY-SA (Creative Commons Attribution-Sharealike 4.0) <a href="/facts/Creative_Commons_licenses/6AV3V7UJ">CC BY-SA 4.0</a></li>
<li>the C-header and XML-schema files that accompany this document are available under the <a href="http://www.opensource.org/licenses/bsd-license.html">BSD</a> license with the extension that modifications must also be provided under the BSD license.</li></ul>
<h2 id="architecture">Architecture</h2>
<p>Each FMU (Functional Mock-up Unit) is distributed in a <a href="/facts/ZIP_(file_format)/qDrrYIB9">zip file</a> with the extension ".fmu" which contains:<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>
</p>
<ul><li>an XML file containing among other things the definition of the variables used by the FMU;</li>
<li>all the equations used by the model (defined as a set of <a href="/facts/C_(programming_language)/Ky2No763">C</a> functions);</li>
<li>optional other data, such as parameter tables, user interface, documentation which may be needed by the model.</li></ul>
<h2 id="example">Example</h2>
<p>Below is an example of an FMI model description issued from <a href="/facts/Modelica/pjWEmtEL">Modelica</a>.
</p>
<?xml version="1.0" encoding="UTF8"?>
<fmiModelDescription
  fmiVersion="1.0"
  modelName="ModelicaExample"
  modelIdentifier="ModelicaExample_Friction">
...
  <UnitDefinitions>
     <BaseUnit unit="rad">
        <DisplayUnitDefinition displayUnit="deg" gain="23.26"/>
     </BaseUnit>
  </UnitDefinitions>
  <TypeDefinitions>
     <Type name="Modelica.SIunits.AngularVelocity">
        <RealType quantity="AngularVelocity" unit="rad/s"/>
     </Type>
  </TypeDefinitions>
  <ModelVariables>
     <ScalarVariable
        name="inertia1.J"
        valueReference="16777217"
        description="Moment of inertia"
        variability="parameter">
        <Real declaredType="Modelica.SIunits.Torque" start="1"/>
     </ScalarVariable>
...
  </ModelVariables>
</fmiModelDescription>

<h2 id="comparison-to-simulink-s-functions">Comparison to Simulink S-Functions</h2>
<p>FMI is often compared to <a href="/facts/Simulink/H12XCsw9">Simulink</a> S-Functions since both technologies can be used to integrate third-party tools together.  S-Functions are used to specify a computer language description of a dynamic system. They are compiled as MEX-files that are dynamically linked into <a href="/facts/MATLAB/qPjLISCk">MATLAB</a> when needed. S-Functions use a calling syntax that interacts with Simulink’s equation solvers. This interaction is similar to the interaction that takes place between built-in Simulink blocks and the solvers.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>FMI proponents explain that FMI models have several advantages over Simulink S-Functions:<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<ul><li>S-Functions format is proprietary, whereas the FMI schema is licensed under a <a href="/facts/BSD_licenses/XLtmLp5x">BSD license</a>.</li>
<li>The building blocks of S-Functions are much more complex than FMI, making it very difficult to integrate in simulators other than Simulink itself.</li>
<li>Furthermore, the S-Functions format is specific to Simulink.</li>
<li>S-Functions are not suited for <a href="/facts/Embedded_system/a4muX1wU">embedded systems</a>, due to the memory overhead of S-Functions.</li></ul>

<h2 id="system-structure-and-parameterization-ssp">System Structure and Parameterization (SSP)</h2>
<p>System Structure and Parameterization (SSP)<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> is a companion standard to FMI that defines a standardized, open file format to describe complex, hierarchical (technical) systems, that can be simulated. An SSP file contains definitions for system
architecture, the interfaces of the system elements, and their connections and parameterization.
The aim of SSP is to simplify the exchange and integration of system elements that are used in the
distributed development of a system to be simulated using a wide variety of tools.
<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
</p><p>SSP is being developed as a project of the Modelica Association and is based
on the FMI specification. FMI enables the exchange of individual simulation
components, while SSP enables the exchange of complete simulation systems, their variants and
parameterization. The simulation components of a simulation system described in SSP can also be
independent of FMI and map to other implementations.
</p><p>SSP is extensible to support specific requirements or domain-specific extensions: e.g. OSI, documentation of requirements, traceability or process steps, etc. SSP is open with regard to the component formats. Although it was based on FMI, it can also be used with components specifications of any other format.
</p>
<h2 id="accompanying-standards-and-recommendations">Accompanying standards and recommendations</h2>
<p>In May 2014, the project group Smart Systems Engineering (SmartSE) of the <a href="/facts/ProSTEP_iViP/1Nggk5lG">ProSTEP iViP</a> Association published its Recommendation PSI 11 for the cross-company behavior model exchange.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> FMI thereby is the technological basis. The PSI 11 specifies interaction scenarios, use cases, a reference process and templates, which thereby could ease the industrial application. End of 2016 the group published a movie, which should highlight the industrial benefits.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/20-sim/NCx5meNI">20-sim</a></li>
<li><a href="/facts/Modelica/pjWEmtEL">Modelica</a></li>
<li><a href="/facts/Simulink/H12XCsw9">Simulink</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="http://functional-mockup-interface.org/">FMI main site</a></li>
<li><a href="http://ssp-standard.org/">SSP main site</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Functional Mockup Interface (FMI)". modelica.org. January 2010. Retrieved 2011-12-22. On Jan. 26, version 1.0 of the open Functional Mockup Interface was released (FMI for model exchange 1.0). This interface was developed in the ITEA2 MODELISAR project to support the model exchange between modelling and simulation tools. The Modelisar project is coordinated by Dassault Systèmes. The FMI development has been organized by Daimler. <a href="https://www.modelica.org/publications/newsletters/2010-1/index_html#item8" target="_blank">https://www.modelica.org/publications/newsletters/2010-1/index_html#item8</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Functional Mockup Interface (FMI)". modelica.org. January 2010. Retrieved 2011-12-22. On Jan. 26, version 1.0 of the open Functional Mockup Interface was released (FMI for model exchange 1.0). This interface was developed in the ITEA2 MODELISAR project to support the model exchange between modelling and simulation tools. The Modelisar project is coordinated by Dassault Systèmes. The FMI development has been organized by Daimler. <a href="https://www.modelica.org/publications/newsletters/2010-1/index_html#item8" target="_blank">https://www.modelica.org/publications/newsletters/2010-1/index_html#item8</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Stepan Ozana; Martin Pies. "Using Simulink S-Functions with Finite Difference Method Applied for Heat Exchangers" (PDF). Proceedings of the 13th WSEAS International Conference on SYSTEMS). Retrieved 2015-08-05. <a href="http://www.wseas.us/e-library/conferences/2009/rodos/SYSTEMS/SYSTEMS26.pdf" target="_blank">http://www.wseas.us/e-library/conferences/2009/rodos/SYSTEMS/SYSTEMS26.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Martin Otter; Hilding Elmqvist; Torsten Blochwitz; Jakob Mauss; Andreas Junghanns; Hans Olsson. "Functional Mockup Interface – Overview" (PDF). synchronics.inria.fr. INRIA. Archived from the original (PDF) on July 20, 2011. Retrieved 2011-01-23. <a href="https://web.archive.org/web/20110720233637/http://synchronics.inria.fr/lib/exe/fetch.php/modelica-fmi-elmqvist.pdf" target="_blank">https://web.archive.org/web/20110720233637/http://synchronics.inria.fr/lib/exe/fetch.php/modelica-fmi-elmqvist.pdf</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"SSP Standard Webpage". Modelica Association Project SSP. 2023. Retrieved 2023-05-11. <a href="https://ssp-standard.org/" target="_blank">https://ssp-standard.org/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Hällqvist, Robert; Munjulury, Raghu Chaitanya; Braun, Robert; Eek, Magnus; Krus, Petter (2021). "Engineering Domain Interoperability Using the System Structureand Parameterization (SSP) Standard". Proc. 14th Modelica Conference. doi:10.3384/ecp2118137. <a href="https://ecp.ep.liu.se/index.php/modelica/article/view/180/140" target="_blank">https://ecp.ep.liu.se/index.php/modelica/article/view/180/140</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>ProSTEP iViP Recommendation PSI 11, Smart Systems Engineering, Behavior Model Exchange, V 1.0, May 2014. <a href="http://www.prostep.org/en/medialibrary/publications/recommendations-standards.html#c1077" target="_blank">http://www.prostep.org/en/medialibrary/publications/recommendations-standards.html#c1077</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>Benefits of utilizing FMI for realizing cross-company Systems Engineering, Status February 2017 <a href="https://www.youtube.com/watch?v=A-3iIot0fO8&t=52s" target="_blank">https://www.youtube.com/watch?v=A-3iIot0fO8&t=52s</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
</ol>

Functional Mock-up Interface open-in-new

Functional Mock-up Interface