Each global feature is either the Pointwise mutual information (PMI) or normalized Google distance (NGD) of a pair of concepts in the set, calculated in terms of the sets of concepts that either (1) link to each concept in the pair, (2) are linked to from each concept in the pair, or (3) are in the intersection of the sets defined in (1) and (2), for each concept in the pair 10 .
gLOW attempts to solve the following optimization problem for a given document d: Where Γ * is the optimal output.