As mentioned in Notifications System Architecture, a notification consists of two parts:
- The Notification Item: This encompasses general attributes such as the type of notification, its start and end dates, the course for which it was created, and so on.
- The Notification Recipients: This defines who will actually be receiving it. Typically each notification will have multiple recipients.
Of the two, recipients will be greater in number.
Notification items are deleted under the following circumstances:
- When its corresponding item is deleted or made unavailable.
- When its parent course is deleted.
So, notification items are not deleted very often. Blackboard Learn errs on the side of keeping these items around for a long time, mostly for bookkeeping reasons.
Notification recipients are deleted under the following circumstances:
- When their associated notification item is deleted.
- When the user explicitly deletes a notification from one of the views.
- When it is replaced by overriding notification. For example, an Assignment Submitted notification will replace the Assignment Due notification for the same user and assignment.
- When enough time has passed that the notification is considered "stale" and can be removed. This period of time can be configured at both the system and user level, which is to say that the system as a whole specifies the lifetime of notifications but individual users can choose to clear out notifications on their own timetable.
Some recipients are removed in name only. That is, their associated records actually remain and are merely marked with a DELETED status.