Determining exclusion efficiencies of a plurality of keywords appearing in a search result of an exclusion keyword for indicating efficient exclusion of an unwanted piece of data when the user narrows searching objects. The determining of exclusion efficiencies may involve a processor to calculate an exclusion efficiency for each of a plurality of keywords, if a search condition is applied to the search result and the keyword is applied as an exclusion keyword to the search result. The exclusion efficiency of each of the plurality of keywords provides an indication regarding the effectiveness of exclusion of the keyword.