In {HEAD ~ a tracking hierarchy} all the relations between {TAIL ~ the relation nodes} are known to the tracking system 
In { HEAD ~ a tracking hierarchy } all the relations between { TAIL ~ the relation nodes } are known to the tracking system
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH