To accomplish that we define our objective function as a Constrained Conditional Model (CCM) (Roth and Yih, 2004;Chang et al., 2012) that is used to reward or penalize a pair of candidates t k i , t l j by w (k,l) ij when they are chosen in the same document.
we choose the assignment Γ D that optimizes: Integral constraints Note that as in most NLP problems, the problem is very sparse, resulting in a tractable ILP that is solved quickly by off-the-shelf ILP packages (Gurobi Optimization, 2013).