(2016a) to select nodes from G (i.e., to extract tokens from the text), we frame the keyword identification problem as the maximization of a set function under a budget constraint.
we define a keyword quality function f that not only measures the cumulative CoreRank score of a given set of terms S, but also the density of the subgraph they induce: where λ is a trade-off parameter, and the set function h counts the number of edges that should be added to the subgraph induced by S to make it complete: where |S|, resp.