Aggregated type homogeneity

Developers
1

When aggregating with IfcRelAggregates, is there any restriction on homogeneity of aggregated objects, be it similar concrete entity type or uniformity of some attribute value? As an example, consider decomposition of an entity of type IfcBuilding with default value ELEMENT for composition type: Is there any limitation denoting that aggregated objects be of the same entity type and composition type, e.g. either one of IfcBuilding/PARTIAL, IfcBuildingStorey/COMPLEX, IfcBuildingStorey/ELEMENT or can these appear mixed among the related objects of the aggregation relation?

I did not find any such restriction, neither in formal nor informal IFC specification, but did not go through MVDs. Maybe I overlooked something or is there some restriction as per any official MVD, implementers agreement or the like?

2

Perhaps this note is some kind of a rule about IfcBuilding decomposition?

https://standards.buildingsmart.org/IFC/RELEASE/IFC4/ADD2_TC1/HTML/link/ifcbuilding.htm

NOTE By using the inverse relationship IfcBuilding.IsDecomposedBy it references IfcBuilding || IfcBuildingStorey through IfcRelAggregates.RelatedObjects . If it refers to another instance of IfcBuilding, the referenced IfcBuilding needs to have a different and lower CompositionType , i.e. ELEMENT (if the other IfcBuilding has COMPLEX), or PARTIAL (if the other IfcBuilding has ELEMENT).

Wouldn’t general homogeneity restrictions be weird for building elements aggregations though? :thinking: They could be used for all kinds of stuff.

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