HistoricalEventNodesare Objectsor Viewsin the AddressSpacethat expose historical Events. These Nodesare identified via the EventNotifier Attribute, and provide some historical subset of the Eventsgenerated by the Server.

Each HistoricalEventNodeis represented by an Objector View with a specific set of Attributes. The HistoricalEventFilter Propertyspecifies the fields available in the history.

Not every Objector Viewin the AddressSpacemay be a HistoricalEventNode. To qualify as HistoricalEventNodes, a Nodehas to contain historical Events. To see if historical Eventsare available, a Clientwill look for the HistoryRead/Write states in the EventNotifier Attribute. See OPC 10000-3for details on the use of this Attribute.

Figure 4illustrates the basic AddressSpaceModel of an Event that includes History.

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Figure 4– Representation of an Event with History in the AddressSpace