16. The computer system of claim 15 , wherein filtering the potential variation-phrase pairs to remove those potential variation-phrase pairs that do not satisfy a predetermined criteria comprises, for each discrete subset of potential variation-phrase pairs in the variation-phrase set, recursively pruning potential variation-phrase pairs from the current discrete subset of potential variation-phrase pairs until a predetermined pruning criteria is satisfied.
16. The computer system of claim 15 , wherein filtering the potential variation-phrase pairs to remove those potential variation-phrase pairs that do not satisfy a predetermined criteria comprises, for each discrete subset of potential variation-phrase pairs in the variation-phrase set, recursively pruning potential variation-phrase pairs from the current discrete subset of potential variation-phrase pairs until a predetermined pruning criteria is satisfied. 17. The computer system of claim 16 , wherein pruning potential variation-phrase pairs from the current discrete subset of potential variation-phrase pairs comprises: for each potential variation-phrase pair in the current discrete subset: clustering the potential variation-phrase pairs into at least one cluster set according to cumulative scores corresponding to each potential variation-phrase pair, and deleting those potential variation-phrase pairs from the current discrete subset of potential variation-phrase pairs that fall into the cluster set corresponding to the cluster of potential variation-phrase pairs with the lowest cumulative scores; and determining a co-citation score for each variation-phrase pair with regard to other variation-phrase pairs in the discrete subset of potential variation-phrase pairs, and pruning each potential variation-phrase pair from the discrete subset of potential variation-phrase pairs where the co-citation score falls below a co-citation threshold.