HistoricalDataNodes are always a part of other Nodes in the AddressSpace. They are never defined by themselves. A simple example of a container for HistoricalDataNodes would be a “Folder Object”.
Figure 3 illustrates the basic AddressSpace Model of a DataVariable that includes History.
Figure 3 – Historical Variable with Historical Data Configuration and Annotations
Each HistoricalDataNode with history shall have the Historizing Attribute (see OPC 10000-3) defined and may reference a HistoricalAccessConfiguration Object. In the case where the HistoricalDataNode is itself a Property then the HistoricalDataNode inherits the values from the Parent of the Property.
Not every Variable in the AddressSpace might contain history data. To see if history data is available, a Client will look for the HistoryRead/Write states in the AccessLevel Attribute (see OPC 10000-3 for details on use of this Attribute).
Figure 3 only shows a subset of Attributes and Properties. Other Attributes that are defined for Variables in OPC 10000-3, may also be available.