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 DataVariables 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 node 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.