The NotificationMessage structure used in the Subscription Service set allows specifying different types of NotificationData. The NotificationData parameter is an extensible parameter whose structure depends on the type of Notification being sent. This parameter is defined in Table 164. Other types can be defined by additional parts of OPC 10000 or other specifications based on OPC UA. The ExtensibleParameter type is defined in 7.17.

There may be multiple notifications for a single MonitoredItem in a single NotificationData structure. When that happens the Server shall ensure the notifications appear in the same order that they were queued in the MonitoredItem. These notifications do not need to appear as a contiguous block.

Table 164 – NotificationData parameterTypeIds

Symbolic Id	Description
DataChange	Notification data parameter used for data change Notifications.
Event	Notification data parameter used for Event Notifications.
StatusChange	Notification data parameter used for Subscription status change Notifications.