Subtypes inherit the fully-inherited parent type’s InstanceDeclarations.
As long as those InstanceDeclarations are not overridden they are not referenced by the subtype. InstanceDeclarations can be overridden by adding References, changing References to reference different Nodes, changing References to be subtypes of the original ReferenceType, changing values of the Attributes or adding optional Attributes. In order to get the full information about a subtype, the inherited InstanceDeclarations have to be collected from all types that can be found by recursively following the inverse HasSubtype References from the subtype. This collection of InstanceDeclarations is called the fully-inherited InstanceDeclarationHierarchy of a subtype.
The remainder of 6.3.3 define how to construct the fully-inherited InstanceDeclarationHierarchy and how InstanceDeclarations can be overridden.