The hierarchical lexical database approach can be reclassified into three groups according to usages of the database: gloss based method [5] , conceptual density based method [6, 7] and relative based method<cite> [8,</cite> 9, 10] . Since our method is a kind of the relative based method, this section describes the related works of the relative based method. <cite>[8]</cite> introduced the relative based method using International Roget's Thesaurus as a hierarchical lexical database.