Further, {TAIL ~ the topology service} may create, from a specified topology, {HEAD ~ a directed acyclic graph} and corresponding closure table 
Further , { TAIL ~ the topology service } may create , from a specified topology , { HEAD ~ a directed acyclic graph } and corresponding closure table
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH