When this structure is used for reading ModifiedEvents (isReadModified is set to TRUE), it reads the ModifiedEvents, modification type, the user identifier, and the timestamp of the modification from the history database for the specified time domain for one or more HistoricalDataNodes. If there are multiple replaced Events the Server shall return all of them. The updateType specifies what Event is returned in the modification record. If the updateType is INSERT the Event is the new Event that was inserted. If the updateType is anything else the Event is the old Event that was changed. See 6.9 HistoryUpdateDetails parameter for details on what updateTypes are available.

The purpose of this function is to read Events from history that have been Modified.

The startTime and endTime are used to filter on the Time field for Events.

The domain of the request is defined by startTime, endTime, and numValuesPerNode; at least two of these shall be specified. If endTime is less than startTime, or endTime and numValuesPerNode alone are specified, then the data shall be returned in reverse order with the later data coming first. If all three are specified then the call shall return up to numValuesPerNode results going from StartTime to EndTime, in either ascending or descending order depending on the relative values of StartTime and EndTime. If numValuesPerNode is 0 then all of the Events in the range are returned.

It is specifically allowed for the startTime and the endTime to be identical. This allows the Client to request the Event(s) at a single instance in time. When the startTime and endTime are identical then time is presumed to be flowing forward. If no Events exists at the time specified then the Server shall return the Good_NoData StatusCode.

The standard ContinuationPoint rules (see 6.3) apply. In addition, the following ContinuationPoint rule applies to ReadEventDetails. If a startTime, endTime and numValuesPerNode are all provided, and if more than numValuesPerNode Events exist within that time range for a given Node, then only numValuesPerNode Events per Node are returned along with a ContinuationPoint.

For an interval in which no Events exists, the corresponding StatusCode shall be Good_NoData.

The filter parameter is used to determine which historical Events and their corresponding fields are returned. It is possible that the fields of an EventType are available for real time updating, but not available from the Historian. In this case a StatusCode value will be returned for any Event field that cannot be returned. The value of the StatusCode shall be Bad_NoData.

When reading Events, TimestampsToReturn only applies to Event fields that are of type DataValue. If the requested TimestampsToReturn is not supported for an Event field then the returned value of the Event field is the Bad_TimestampNotSupported StatusCode.