16. The computer-readable storage medium of claim 15 wherein the identifying includes ranking phrases within the papers of a topic based on descriptiveness of the topic.
16. The computer-readable storage medium of claim 15 wherein the identifying includes ranking phrases within the papers of a topic based on descriptiveness of the topic. 17. The computer-readable storage medium of claim 16 wherein the ranking of phrases includes: ranking two-word phrases within the papers; selecting high ranking two-word phrases; and repeatedly extending the selected phrases based on the ranking of the extended phrases.