Historical Update and Read|OPC UA Standard|Forum|OPC Foundation

Hello everyone,

At the moment, I’m trying to implement historical update support, but I’m not clear on the following – should I return data that comes from INSERT_1, REPLACE_2, UPDATE_3 as the result of a raw historical read? And how to do it correctly?

I am confused by the following phrase from the specification (regarding Read raw functionality):

…it reads the values, qualities, and timestamps from the history database for the specified time domain for one or more HistoricalDataNodes. This parameter is intended for use by a Client that wants the actual data saved within the historian

Since the modified values are not the ones that were saved by the historian, they should not be the result of a raw reading, but at the same time, the specification defines the following:

For cases where there are multiple values for a given timestamp, all but the most recent are considered to be Modified values and the Server shall return the most recent value. If the Server returns a value which hides other values at a timestamp then it shall set the ExtraData bit in the StatusCode associated with that value.

Thanks.