Question regarding the * symbol in an ifc-step file
So for example here there is * as the first attribute of IfcSIUnit:
The first attribute as in the documentation should be a IfcDimensionalExponents
However instead of #28= IFCSIUNIT(#30,.LENGTHUNIT.,$,.METRE.); it is #28= IFCSIUNIT(*,.LENGTHUNIT.,$,.METRE.);
So in the wiki about the step file it's reads:
Explicit attributes which got re-declared as derived in a subtype are encoded as "*" in the position of the supertype attribute.
However i don't unterstand the use of * at all.
The ifc file is from here https://github.com/buildingSMART/Sample-Test-Files/blob/master/IFC 4.0/BuildingSMARTSpec/air-terminal-element.ifc
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Comments
This was discussed a little here:
https://community.osarch.org/discussion/comment/12231/#Comment_12231
Generically, what would this be called in computer science?
I've called them "derived attributes", because their value is automatically derived by the rules in the schema.