In OPC UA models, there are also attributes that only appear on data types and reference types that do not get propagated to instances, but in AML, the corresponding AML attribute types and AML interface classes, when instantiated propagate all the attributes associated with the type. In cases where the value of an attribute only has meaning on a type, the attribute shall contain an entry in the Additional Information collection of the Header “OPC:TypeOnly” to indicate that the attribute only has meaning on the type and can ideally be deleted or at least ignored on instances as shown in Figure A.20. Engineering tools should delete attributes marked “OPC:TypeOnly” when creating instances on export. Engineering tools shall ignore attributes marked “OPC:TypeOnly” on import in cases where the exporting tool fails to delete them when creating the instance.

Figure A.20 – “OPC:TypeOnly” additional Information in Header