10. A computer implemented method for maintaining a database of source documents, comprising: for a plurality of received source documents having content to compare against received target documents, determining fragments of content in the received source documents; calculating a fingerprint for each of the determined fragments; determining metadata for the determined fragments, wherein the determined metadata includes fragment specific information providing additional information from metadata for the source documents including the determined fragments; and associating with each determined fragment the calculated fingerprint and the determined metadata, wherein the database stores, for each determined fragment the associated calculated fingerprint and the determined metadata.
11. The method of claim 10 , wherein the metadata for each of the determined fragments includes at least one of metadata for the received source document and metadata specific to the determined fragment.