19. The method of claim 13 , further comprising: locating documents, using the computer-implemented device, in the first and second sets of documents that are identical; and removing the documents, using the computer-implemented device, in the first and second sets of documents that are identical from the first and second sets of documents before constructing the index.
20. The method of claim 19 , where locating the documents in the first and second sets of documents that are identical includes: locating the documents, using the computer-implemented device, in the first and second sets of documents that are identical based on checksum values calculated for each of the documents in the first and second sets of documents.