39. The system of claim 37 , wherein the operations further comprise recommending content related to a given electronic document based on information contained in the category graph.
39. The system of claim 37 , wherein the operations further comprise recommending content related to a given electronic document based on information contained in the category graph. 40. The system of claim 39 wherein recommending content based on the category graph further comprises excluding document categories associated with n-grams whose count is below a threshold.