There are different ways of extending an existing UA model without losing backward compatibility. The existing model might be defined in a companion specification (or vendor specification), and the specification could be extended to include OPC UA FX as part of its model. These additions could be accomplished using Interfaces or via AddIns; examples of both are provided.
Figure B.2 illustrates the original model defined in the example specification. The illustration shows a model that uses an Interface from OPC 10000-100, but this would not be required. It is included to help illustrate a model that might already include some functionality used by OPC UA FX. The illustration also shows an instance of the type defined by the model and a folder structure for that instance that is part of the example specification model.