6.4.4.2 Subtyping Rules for Properties of ModellingRules

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 21 specifies the allowed changes on the Properties when overriding the ModellingRules in the subtype.

Table 21 – Rule for ModellingRules Properties when Subtyping
ModellingRule on supertypeModellingRule on subtype
MandatoryMandatory
OptionalMandatory or Optional
MandatoryPlaceholderMandatoryPlaceholder
OptionalPlaceholderMandatoryPlaceholder or OptionalPlaceholder