15. The apparatus for presenting information of document files according to claim 6 , wherein: total weight values for a plurality of document files are calculated, the total weight values are plotted in a numerical line, distances between adjacent values on the numerical line are calculated, a great distance having a significant difference is found based on a statistical check, a separation point is set where the significant difference appeared, and document files whose total weight value is higher than the separation point are selected as representative document files.
6. An apparatus for presenting information of document files, the document files being stored on a document database where the document files are categorized and stored into any of predefined category bins, the apparatus comprising: a selecting section that selects at least some of document files stored on the document database and categorized in object category bins as representative document files for each of the object category bins, the object category bins being at least part of the category bins, the representative document files comprising a proper subset of the document files categorized in each respective object category bin associated with the representative document files; and a presenting section that presents information extracted from the selected representative document files to a user when the user queries contents of an object category bin of the object category bins without entering the object category bin, wherein the presenting section presents a guide caption describing keywords extracted from a file and obtained by a document summarizing process, and the presenting section increases a highlight contrast to a background for guide captions of files having greater weights regarding access histories.