New ModellingRuleshave to be defined if the predefined ModellingRulesare not appropriate for the model exposed by the Server.

Depending on the model used by the underlying system the Servermay need to define new ModellingRules, since the OPC UA Servermay only pass the data to the underlying system and this system may use its own internal rules for instantiation, subtyping, etc.

Beside this, the predefined ModellingRulesmight not be sufficient to specify the required behaviour for instantiation and subtyping.