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IFC4 RV 1.2 shcema issue

What is the difference between IFC release and MVD? Can two MVDs for the same IFC versions can have different schemas?

Until recently the answer was - No. All MVDs for the same IFC versions used to work on one EXPRESS schema and MVDxml was to describe restrictions.

But for IFC 4 RV 1.2 release we have got schemes (EXP files) different.

It uses IfcStrippedOptional to prohibit some optional attributes, for example https://standards.buildingsmart.org/MVD/RELEASE/IFC4/ADD2_TC1/RV1_2/HTML/

Why it was not done in mvdXML?

  • Tools generate early-binding API from EXPRESS scheme. Now they will create different libraries for RV and others IFC4 mvds.
  • Consequently, applications should build different export/import libraries if use early-binding.
  • The construction that looks uncertain and unclear. It leaves the attribute optional but specifies some singular datatype.
  • Particularly for this case MVD should require value FALSE rather then $ to be more clear

Can we rollback this scheme difference?
@TLiebich, @mweise

Hi Igor, actually it is not new - publishing a subset schema for an MVD has started a few years ago. Also at that time we made clear, that the subset EXPRESS schema is meant solely for a checker, to run a base check to varify, that the ifc file conforms to the MVD (does not contain additional content). So it is used to formalize the restrictions.

So on your side, you should NOT use the subset schema, but only the EXPRESS schema for IFC4 Add2 TC1. The same EXPRESS schema is used for all MVD implementations.

Remark: yes, the documentation is not very clear about it - something to be improved. I hope, that once we have the fully IFC specification on github, many more people can help to complete the documentation.

So under https://standards.buildingsmart.org/MVD/RELEASE/IFC4/ADD2_TC1/RV1_2/HTML/link/annex-a.htm - the full IFC4 Add2 TC1 EXPRESS and XSD schema should be linked, and under https://standards.buildingsmart.org/MVD/RELEASE/IFC4/ADD2_TC1/RV1_2/HTML/link/listing-referenceview_v1-2.htm the subset with a remark that it is for running checks only.

Exporter application may need to know about MVD.
e.g. I am developing one application for RV and DTV, it has configuration file for the MVD specific.

mvdxml is a good configuration file for this role but what do we have now with these attributes broke it…

What is the problem to put the restriction to mvdxml?

mvdXML would be the best way to configure the export (provide a filter that conforms to the MVD). Support for mvdXML is still sparse (and there are some limitations).

Using an MVD specific subset EXPREE file is an alternative way to use it in a parser. As I said before, it is not to parse for your toolbox - here use the combination of IFC4 Add2 TC1 express file and mvdXML.

Side issue - is there a group interested into improving mvdXML (there had been a few initiatives for a binary mvdXML or mvdXML lite)?

1 Like

You have one candidate here in me. But I think you already know that since I have been talking to @mweise. :slight_smile: Would it make sense to create a new topic for this?

@sergej - yes, setting up a new topic is fine - would you go ahead? I assum that also @jonm and @andreas.geiger would be interested and potentially others.