# concept[].definition
The message represents/requests a change that should not be processed more than once; e.g., making a booking for an appointment.

# concept[].definition
The message represents a response to query for current information. Retrospective processing is wrong and/or wasteful.

# concept[].definition
The content is not necessarily intended to be current, and it can be reprocessed, though there may be version issues created by processing old notifications.