There are two different use cases when creating an instance ‘A’ based on a TypeDefinitionNode‘A_Type’. Either ‘A’ is used as normal instance or it is used as an InstanceDeclarationof another TypeDefinitionNode.
In the first case, it is not required that newly created or referenced instances based on InstanceDeclarationshave a ModellingRule, however, it is allowed that they have any ModellingRuleindependent of the ModellingRuleof their InstanceDeclaration.
In the second case, all instances that are referenced directly or indirectly from ‘A’ based on InstanceDeclarationsof ‘A_Type’ initially maintain the same ModellingRuleas their InstanceDeclarations.The ModellingRulesmay be updated; the allowed changes to the ModellingRulesof these Nodes are the same as those defined for subtyping in 188.8.131.52.
In Figure 25an example of such a scenario is given. Type_B uses an InstanceDeclarationbased on Type_A (upper part of the Figure). Later on the ModellingRuleof the InstanceDeclaration A1 is changed (lower part of the Figure). A1 has become the NamingRuleof Mandatory(changed from Optional).