Monitor Historian Subscriptions

Certain objects in the Historian SDK allow you to create subscriptions that fire an event back to the calling application whenever the object's status updates. These subscriptions allow for exception-based monitoring of the Historian status without resorting to intensive polling of the server.

The following table displays the objects and their supported subscription events:

Table 1. Historian Objects with Subscription Events
Object	Subscription Events
Messages Object	AlertReceived and MessageReceived Events
Tags Object	ChangeReceived Event
Data Object	CurrentDataReceived Event
Archives Object	StatusReceived Event
Collectors Object	StatusReceived Event

Subscribing to any of these Object's events allows you to receive direct notification of status changes. For example, using iFIX scripting, you could route this notification to any alarm queue in iFIX.