Additionally, in the described embodiment, {HEAD ~ a dynamic ad placement engine} knows about {TAIL ~ the current context} of the system before an ad request is received 
knows about
Additionally , in the described embodiment , { HEAD ~ a dynamic ad placement engine } knows about { TAIL ~ the current context } of the system before an ad request is received
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH