In an OPC UA Server, Automation Data is represented as a Data Value and and status, in addition additional error data can be provided via Diagnostic Info for a tag
The COM UA Proxy maps the Data Value structure into VQT data and error code.
For successful operations(StatusCode of Good and Uncertain), the COM UA Proxy maps the Status Code of the DataValue to the OPC DA Quality But in case of error(StatusCode of Bad), the Status Code is mapped to the OPC DA Error code.
The StatusCode in the Diagnostic Info returned by the OPC UA Server are mapped to OPC DA Error codes. Figure A.5 illustrates this mapping.