6. The computer program product according to claim 1 , wherein when there are a plurality of electronic documents which reference one of the plurality of pairs of the plurality of electronic documents, calculating the total importance of each of the electronic documents includes calculating the total importance of the one of the pair of electronic documents, on the basis of the total importance of each of the plurality of referencing electronic documents.
6. The computer program product according to claim 1 , wherein when there are a plurality of electronic documents which reference one of the plurality of pairs of the plurality of electronic documents, calculating the total importance of each of the electronic documents includes calculating the total importance of the one of the pair of electronic documents, on the basis of the total importance of each of the plurality of referencing electronic documents. 7. The computer program product according to claim 6 , wherein calculating the total importance includes calculating the total sum of the total importance of each of the referencing electronic documents as the total importance of the one of the plurality of pairs of the plurality of electronic documents.