Patent ID: 7440938

Claim:
A similarity calculation method for calculating similarity among documents in a document search system adapted to search documents registered in advance, comprising: storing, in a storage as a searching index, each of keywords contained in a previously registered document; extracting each of keywords contained in a query inputted by a searcher; deciding an attribute of each of said keywords by referring to an element-type dictionary which provides correspondence relationships between keywords and attributes; classifying said extracted keywords on an attribute basis in accordance with a result of decision and counting a number of keywords belonging to each of the attributes thus classified to determine a count number of each of the attributes; comparing said count numbers of attributes thus determined with count numbers of corresponding attributes of said previously registered document; calculating similarity between said query and said previously registered document on a basis of comparison of said count numbers; and wherein the searching index stores character strings with respect to a plurality of previously registered documents; wherein at least one keyword of the keywords contained in the query is decided as a first group of the keywords, and at least one different keyword of the keywords is decided as a second group of the keywords; wherein the deciding, classifying, counting, comparing and calculating operations are performed for the first group of the keywords to determine a first subset of the previously registered documents having similarity to the at least one keyword, and are separately performed for the second group of the keywords to determine a second subset of the previously registered documents having similarity to the at least one different keyword; the similarity calculation method further comprising: determining any previously registered documents which are common to both the first and second subsets to narrow-down to documents having similarity to said query.