1. A computer implemented document processing method comprising: accessing a plurality of initial documents; initially processing the initial documents to provide a plurality of initial representations for respective ones of the initial documents, wherein the initial representations include a plurality of associations of the initial documents with a plurality of features which occur in respective ones of the initial documents; using the initial representations, initially identifying a plurality of associations of the initial documents with respect to one another; after the initially identifying, accessing a plurality of subsequent documents; subsequently processing the subsequent documents to provide a plurality of subsequent representations for respective ones of the subsequent documents, wherein the subsequent representations include a plurality of associations of the subsequent documents with a plurality of features which occur in respective ones of the subsequent documents; and using the initial and subsequent representations, subsequently identifying a plurality of associations of the initial documents with respect to the subsequent documents.