A. It is a kind of watcher that requests a one-time view of the user's current presentity information, but does not get future presentity information for a user.

B. It is a user whose devices are sending status or presentity information on his behalf using a Publish message regarding his communication status.

C. It is a watcher that is subscribing to current and future presentity information from another user.

D. It is the presence information about a user that the system reports.