9. The computer system of claim 8 , wherein the comparing the plurality of digital text volumes comprises: determining a set of representative features for a digital text volume; applying a plurality of hash functions to the set of representative features to produce a plurality of hash values for each hash function; selecting, for each hash function, a minimum hash value from among the hash values produced by applying that hash function to the set of representative features to produce a reduced feature set containing selected minimum hash values for the digital text volume; and comparing the reduced feature set for the digital text volume to reduced feature sets for other digital text volumes to produce the volume similarity data.
9. The computer system of claim 8 , wherein the comparing the plurality of digital text volumes comprises: determining a set of representative features for a digital text volume; applying a plurality of hash functions to the set of representative features to produce a plurality of hash values for each hash function; selecting, for each hash function, a minimum hash value from among the hash values produced by applying that hash function to the set of representative features to produce a reduced feature set containing selected minimum hash values for the digital text volume; and comparing the reduced feature set for the digital text volume to reduced feature sets for other digital text volumes to produce the volume similarity data. 10. The computer system of claim 9 , wherein the comparing the reduced feature set for the digital text volume to the reduced feature sets for the other digital text volumes comprises: determining a number of minimum hash values in the reduced feature set for the digital text volume that are in common with minimum hash values in a reduced feature set of a second digital text volume in the corpus.