[   l e x i c a l   c o h e s i o n   &   w o r d n e t   ]

One valuble preexisting lexicon for lexical cohesion and collocation is the thesaurus.

A thesaurus is a network of nodes (word) and edges (relations).

Semantic relation can be measured in terms of distance in a thesaurus.

Subject and topic transition and detection can be performed using this information by finding dense word cluster representation across any given input.