An Element with a Type that has a TypeKind of “StrongReference” contains an “exclusive” / “owning” (one-to-one) reference to an Object. So, more verbosely it is a “Strong Object Reference”.

Facets are prohibited for Types with a TypeKind of “StrongReference”.

Each Type with a TypeKind of “StrongReference” must state the target Group of the reference using the BaseType field. References can be made to instances of this Group or its descendants / sub-classes.