The DataVariable or Object that has Annotation data will add the Annotations Property as shown in Table 2.
Table 2 – Annotations Property
|Annotations||O||Annotation||The Annotations Property is used to indicate that the history collection exposed by a HistoricalDataNode supports Annotation data. Annotation DataType is defined in Subclause 5.5.|
Since it is not allowed for Properties to have Properties, the Annotations Property is only available for DataVariables or Objects.
The Annotations Property shall be present on every HistoricalDataNode that supports modifications, deletions, or additions of Annotations weather or not Annotations currently exist. Annotation data is accessed using the standard HistoryRead functions. Annotations are modified, inserted or deleted using the standard HistoryUpdate functions and the UpdateStructuredDataDetails structure. The presence of the Annotations Property does not indicate the presence of Annotations on the HistoricalDataNode.
A Server shall add the Annotations Property to a HistoricalDataNode only if it will also support Annotations on that HistoricalDataNode. See OPC 10000-4 for adding Properties to Nodes. A Server shall remove all Annotation data if it removes the Annotations Property from an existing HistoricalDataNode.
As with all HistoricalNodes, modifications, deletions or additions of Annotations will raise the appropriate Historical Audit Event with the corresponding NodeId.