16. The non-transitory computer-readable storage medium of claim 15 , 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.
16. The non-transitory computer-readable storage medium of claim 15 , 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. 17. The non-transitory computer-readable storage medium of claim 16 , 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.