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Reading the new FMI 3 proposal I'm wondering if it is possible to generate one FMU zip file including one compiled model which supports both FMI 2 and FMI 3?

A compiled model could contain the necessary fmi2...() and fmi3...() functions and therefore support both. But my feeling is that the XML file is not able to state that it is supporting both. Is this correct?

Thanks for an answer.

ingo-d
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    FMI2 was not backwards compatible with FMI1 so as far as I know same goes for FMI3. I guess tools could support all if needed but you probably cannot pack them in the same zip. – Adrian Pop May 07 '21 at 16:10
  • The other answers are correct; it is not possible for an FMU to comply with both FMI2 and FMI3. What could be an option: to use the SSP standard https://ssp-standard.org/publications/SSP10/SystemStructureAndParameterization10.pdf (once it supports FMI3) to define two variants of the systems structre definition (.ssd) where one of them uses the FMI2 FMU and the other the FMI3 FMU. – Christian Bertsch May 08 '21 at 08:15
  • @ChristianBertsch Thanks for the SSP standard hint... . I think the transition time from FMI2 to FMI3 will essentially need such a meta standard. Is there already a rough timeline for supporting FMI3? – ingo-d May 11 '21 at 07:58

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The FMU cannot support both in a compliant way.

FMI 2 (including 2.0.2) should according to https://fmi-standard.org/ have a modelDescription.xml with

<fmiModelDescription
  fmiVersion="2.0"

FMI 3 https://fmi-standard.org/docs/3.0-dev/#fmiModelDescription is planned to have version "3.0" (or possibly variants of this for pre-releases and future minor versions).

Having two different xml-files and switching between them might be possible.

Hans Olsson
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  • Thanks for your answer. As vendors and customers of models enjoy having the FMU in one zip file only it would be a great breakthrough supporting this feature further on. A simple FMU approach: * the XML files have to be in the lowest supported version e.g 2.0. * the XML files for higher supported version could be in subfolders of the zip file e.g `SupportedVersions\3.0` and `SupportedVersions\3.1` * `fmiModelDescription` needs an extra attribute `fmiSupportedVersions="3.0,3.1"` Of course the FMI2 needs for this approach a revision but it could be worth ... – ingo-d May 11 '21 at 08:31
  • You could propose it to the FMI Standard issue tracker; but the ones I talked to found it unlikely to be added. Tools can already support import of different FMI versions. – Hans Olsson May 11 '21 at 09:28