Although the composition attribute was made optional in IFC4 for IfcSpatialStructureElement, the description within the derived classes suggests this isn’t advised when nesting instances of a common type. Ie a complex site decomposed into element sites.
I don’t see where rules enforcing this, and I’m questioning whether the documentation needs revision.
I’ve been discussing with government agencies the three level restriction imposed by forcing parent sites (or facilities) to have a different and higher CompositionType. We’d prefer that this restriction wasn’t in place for representing a network.
I’d like to understand the reasoning for imposing the restriction, and whether this might be relaxed for IFC5 or newer versions of IFC4.