We approximate this based on the heuristic that logically consistent paths occur more frequently.
we score this node via Pointwise Mutual Information (PMI) between the partial path c 1−3 and c 4 : Further, it is well known that PMI has high sensitivity to low-frequency values, thus we use normalized PMI (NPMI) (Bouma, 2009): score(c 4 ) = PMI(c 4 , c 1−3 )/(− log P(c 4 , c 1−3 )).