When the Server wants to provide the overall health status of an asset over time, the history of the 2:DeviceHealth Variable shall be used. For each 2:DeviceHealth Variable, where the history is currently tracked, the Historizing Attribute is set to True and the AccessLevel is set to HistoryRead. In order to provide the information, when history tracking started, a HistoryDataConfiguration is referenced with a HasHistoricalConfiguration Reference (see OPC 10000-11 for details).
When the Server wants to provide information for tracking the alarms with detailed health information of an asset over time, the history of the events based on the alarms shall be used. . This specification does not define which Objects are used as EventNotifier. As defined in the base specification, the Server Object shall be an EventNotifier when events are supported, which can be used to subscribe to all events of the Server. It is, therefore, server-specific where the history of events can be accessed and what details of the events are stored. The general concepts are defined in OPC 10000-11. The server should provide for each asset the history of events for the same amount of time as the history of the 2:DeviceHealth.