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 20specifies 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