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