IFC, set a property value N/A or None

edited January 2021 in General

What is the correct way to set a attribut value to n/a in IFC standard https://en.wikipedia.org/wiki/N/A

The background is we have some attributes which do not suit for any object. For example a brick wall does not have a foam work attribute. In our CAD it is much easier to set the attribute to N/A than to remove the attribute. Because for example wall material could change often between bricks and concrete due to wishes of build owner or architects. We would need to remove and add attributes than, which is cumbersome. Much easier would be just to set the attribute value.

Does such n/a exist for all attribute data types? Does it even exist for bool, integer and double?

bernd

Comments

  • You can set to Null / None.

  • @Moult said:
    You can set to Null / None.

    is this how it works in IfcOpenShell or is it IFC standard? Is this handled in IFC standard somewhere? I did not found anything.

    Bernd

  • @bernd it is IFC standard. Btw I think you are referring to properties, not attributes. IFC has the concept of cardinality which allows you to leave things as null. BIM applications typically don't expose and do not distinguish between null vs empty. The upcoming BlenderBIM Add-on will be the first authoring app I know of that does distinguish between these values.

  • edited January 2021

    @Moult said:
    ... I think you are referring to properties, not attributes. ...

    yes, changed the title in this regard

    @Moult said:
    it is IFC standard. .... IFC has the concept of cardinality which allows you to leave things as null.

    What exactly should be put in to make a attribute value null or N/A or None. Does it depend on the property value data type or ist is general. Do you have a link to the IFC Standard.

    @Moult said:
    BIM applications typically don't expose and do not distinguish between null vs empty.

    Exactly for this reason I do ask. ATM I am in contact with Nemetschek Allplan folks and they did answer they are according IFC standard. I am not sure here thus I ask for some more information.

    @Moult said:
    The upcoming BlenderBIM Add-on will be the first authoring app I know of that does distinguish between these values.

    good news

  • @bernd see https://standards.buildingsmart.org/IFC/RELEASE/IFC4/ADD2_TC1/HTML/link/ifcpropertysinglevalue.htm - the cardinality of the NominalValue is set to ? (i.e. it is optional).

    at time 30:22 shows the new BlenderBIM Add-on UI where the blue circles mean it is null and empty, where as the full grey circles mean it is filled in, even if the value is an empty string or falsey.

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