It is allowed that subtypes override ModellingRules on their InstanceDeclarations. As a general rule for subtyping, constraints shall only be tightened, not loosened. Therefore, it is not allowed to specify on the supertype that an instance shall exist with the ModellingRule Mandatory and on the subtype make this ModellingRule Optional. Table 20 specifies the allowed changes on the Properties when overriding the ModellingRules in the subtype.

Table 20 – Rule for ModellingRules Properties when Subtyping

ModellingRule on supertype	ModellingRule on subtype
Mandatory	Mandatory
Optional	Mandatory or Optional
MandatoryPlaceholder	MandatoryPlaceholder
OptionalPlaceholder	MandatoryPlaceholder or OptionalPlaceholder