15. A non-transitory computer-readable storage medium storing executable computer program instructions for identifying relationships between a plurality of digital text volumes in a corpus, the computer program instructions comprising instructions for: comparing the plurality of digital text volumes in the corpus to produce volume similarity data describing similarities among pairs of digital text volumes; identifying a cluster of similar digital text volumes based on the volume similarity data; comparing pages of a pair of digital text volumes within the cluster to determine page similarity data indicating degrees of similarity between the compared pages; extracting signals from the volume similarity data and the page similarity data that describe a relationship between the pair of digital text volumes, the extracted signals including at least one of: a measure of linear page-to-page fit that models text uniformly distributed across pages of the pair of digital text volumes and a measure of relative consecutive page correlation between pages of the pair of digital text volumes; classifying the relationship between the pair of digital text volumes based on the extracted signals; and storing classification data describing the relationship between the pair of digital text volumes.
15. A non-transitory computer-readable storage medium storing executable computer program instructions for identifying relationships between a plurality of digital text volumes in a corpus, the computer program instructions comprising instructions for: comparing the plurality of digital text volumes in the corpus to produce volume similarity data describing similarities among pairs of digital text volumes; identifying a cluster of similar digital text volumes based on the volume similarity data; comparing pages of a pair of digital text volumes within the cluster to determine page similarity data indicating degrees of similarity between the compared pages; extracting signals from the volume similarity data and the page similarity data that describe a relationship between the pair of digital text volumes, the extracted signals including at least one of: a measure of linear page-to-page fit that models text uniformly distributed across pages of the pair of digital text volumes and a measure of relative consecutive page correlation between pages of the pair of digital text volumes; classifying the relationship between the pair of digital text volumes based on the extracted signals; and storing classification data describing the relationship between the pair of digital text volumes. 18. The non-transitory computer-readable storage medium of claim 15 , wherein the comparing pages of the pair of digital text volumes within the cluster to determine the page similarity data comprises: determining a set of representative features for a page of a first digital text volume of the pair of digital text volumes; 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 page; and comparing the reduced feature set for the page to the reduced feature sets for pages of a second digital text volume of the pair of digital text volumes to determine the page similarity data.