ModifiedValues – OPC Unified Architecture – Part 11: Historical Access

3.1.7 ModifiedValues

HistoricalDataNode ’ s value that has been changed (or manually inserted or deleted) after it was stored in the historian

Note 1

Note 1 to entry: For some Servers, a lab data entry value is not a modified value, but if a user corrects a lab value, the original value would be considered a modified value, and would be returned during a request for ModifiedValues. Also manually inserting a value that was missed by a standard collection system can be considered a modified value. Unless specified otherwise, all historical Services operate on the current, or most recent, value for the specified HistoricalDataNode at the specified timestamp. Requests for ModifiedValues are used to access values that have been superseded, deleted or inserted. It is up to a system to determine what is considered a modified value. Whenever a Server has modified data available for an entry in the historical collection it shall set the ExtraData bit in the StatusCode.