code: def _Notify(username, notification_type, message, object_reference):
    
  
    # Do not try to notify system users (e.g. Cron).
    if username in aff4_users.GRRUser.SYSTEM_USERS:
      return
  
    if object_reference:
      uc = object_reference.UnionCast()
      if hasattr(uc, "client_id"):
        message = _HostPrefix(uc.client_id) + message
  
    n = rdf_objects.UserNotification(
        username=username,
        notification_type=notification_type,
        state=rdf_objects.UserNotification.State.STATE_PENDING,
        message=message,
        reference=object_reference)
    data_store.REL_DB.WriteUserNotification(n)
docs: Schedules a new-style REL_DB user notification.