The system also includes {TAIL ~ a subscription mechanism} that sends {HEAD ~ a subscription message} to a notification mechanism 
The system also includes { TAIL ~ a subscription mechanism } that sends { HEAD ~ a subscription message } to a notification mechanism
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH