This annex describes the basic infrastructure to model state machines. It defines ObjectTypes, VariableTypes and ReferenceTypes and explains how they should be used.

This annex is an integral part of this standard, that is, the types defined in this annex have to be used as defined. However, it is not required but strongly recommended that a Server uses these types to expose its state machines. The defined types may be subtyped to refine their behaviour.

When a Server exposes its state machine using the types defined in this annex, it might only provide a simplified view on its internal state machine, hiding for example substates or putting several internal states into one exposed state.

The scope of the state machines described in this annex is to provide an appropriate foundation for state machines needed for OPC 10000-9 and OPC 10000-10. It does not provide more complex functionality of a state machine like parallel states, forks and joins, history states, choices and junctions, etc. However, the base state machine defined in this annex can be extended to support such concepts.

The following clauses describe examples of state machines, define state machines in the context of this annex and define the representation of state machines in OPC UA. Finally, some examples of state machines, represented in OPC UA, are given.