This Clause defines ReferenceTypesthat are needed beyond those already specified as part of OPC 10000-3and OPC 10000-5. This includes extending TwoStateVariableTypestate machines with sub states and the addition of Alarmgrouping.

The TwoStateVariableType Referenceswill only exist when sub states are available. For example, if a TwoStateVariableTypemachine is in a False State, then any sub states referenced from the True state will not be available. If an Event is generated while in the False state and information from the True state sub state is part of the data that is to be reported than this data would be reported as a NULL. With this approach, TwoStateVariableTypescan be extended with subordinate state machines in a similar fashion to the StateMachineTypedefined in OPC 10000-5.