The meta category to which the dimensions which structure the concepts in any conceptualization belong (are instance of), as opposed to structural-concept, which is the meta category which includes the concepts in any conceptualization. In Loom, this includes both relations and properties, but what is meant to be modelled as property is explained in a dedicated annotation.
(<=> (Structuring-Concept ?Self)
(And (Meta-Level-Category ?Self)
(Exists (?A)
(And (Archetype ?Self ?A)
(Or (Relation ?A) (Property ?A))))))