8. A method as recited in claim 1 , wherein generating the extraction complexity feature further comprises: incrementing scores of selected ones of the multiple vertices by propagating a relevance of one or more of the multiple vertices through the undirected graph.
9. A method as recited in claim 8 , wherein generating the extraction complexity feature further comprises: normalizing, after incrementing the scores of the selected ones of the multiple vertices, scores of the multiple vertices to obtain the language model.