HasNotifierand HasEventSource Referencesare used to expose the hierarchical organization of Eventnotifying Objectsand ConditionSources. An Eventnotifying Objectrepresents typically an area of Operatorresponsibility. The definition of such an area configuration is outside the scope of this standard. If areas are available, they shall be linked together and with the included ConditionSourcesusing the HasNotifierand the HasEventSource Reference Types. The Server Objectshall be the root of this hierarchy.
Figure 24shows such a hierarchy. Note that HasNotifieris a sub-type of HasEventSource. I.e. the target Nodeof a HasNotifier Reference(an Eventnotifying Object) may also be a ConditionSource. The HasEventSource Referenceis used if the target Nodeis a ConditionSourcebut cannot be used as Eventnotifier. See OPC 10000-3for the formal definition of these Reference Types.