HistoricalDataNodesare always a part of other Nodes in the AddressSpace.They are never defined by themselves. A simple example of a container for HistoricalDataNodeswould be a “Folder Object”.

Figure 3illustrates the basic AddressSpaceModel of a DataVariablethat includes History.

image006.png

Figure 3– HistoricalVariablewith Historical Data Configuration and Annotations

Each HistoricalDataNodewith 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 Propertythen the HistoricalDataNodeinherits the values from the Parent of the Property.

Not every Variablein the AddressSpace might contain history data. To see if history data is available, a Clientwill look for the HistoryRead/Write states in the AccessLevel Attribute(see OPC 10000-3for details on use of this Attribute).

Figure 3only shows a subset of Attributesand Properties. Other Attributesthat are defined for Variablesin OPC 10000-3, may also be available.