3. The searching apparatus according to claim 2 , wherein said exclusion efficiency is calculated, for an individual keyword associated with said searching object data, based on a first parameter indicating a level of exclusion efficiency of data in a set of part of said searching object data when said keyword is specified as said exclusion keyword and a second parameter indicating a level of exclusion efficiency of data in a set of all of said searching object data when said keyword is specified as said exclusion keyword.
3. The searching apparatus according to claim 2 , wherein said exclusion efficiency is calculated, for an individual keyword associated with said searching object data, based on a first parameter indicating a level of exclusion efficiency of data in a set of part of said searching object data when said keyword is specified as said exclusion keyword and a second parameter indicating a level of exclusion efficiency of data in a set of all of said searching object data when said keyword is specified as said exclusion keyword. 4. The searching apparatus according to claim 3 , wherein said exclusion efficiency increases as the value of said first parameter is smaller, and increases as the value of said second parameter is greater.