HistoricalEventNodes are Objects or Views in the AddressSpace that expose historical Events. These Nodes are identified via the EventNotifier Attribute, and provide some historical subset of the Events generated by the Server.
Each HistoricalEventNode is represented by an Object or View with a specific set of Attributes. The HistoricalEventFilter Property specifies the fields available in the history.
Not every Object or View in the AddressSpace may be a HistoricalEventNode. To qualify as HistoricalEventNodes, a Node has to contain historical Events. To see if historical Events are available, a Client will look for the HistoryRead/Write states in the EventNotifier Attribute. See OPC 10000-3 for details on the use of this Attribute.
Figure 4 illustrates the basic AddressSpace Model of an Event that includes History.
Figure 4 – Representation of an Event with History in the AddressSpace