12. The system of claim 11 , wherein the data store of information is indexed into one or more indexes to facilitate the determining of the first and second data sets.
12. The system of claim 11 , wherein the data store of information is indexed into one or more indexes to facilitate the determining of the first and second data sets. 14. The system of claim 12 , wherein a one of the indexes comprises an index of all users indexed by corresponding user IDs that includes, for each particular user ID, the set of concept nodes identified by corresponding concept IDs that are connected to the user node corresponding to the particular user ID in the index.