10. The apparatus of claim 9, wherein the determining means decides based on the output of the analyzing means that if the perplexity value for the database decreases, the candidate phrase is added to the database as a superword.
10. The apparatus of claim 9, wherein the determining means decides based on the output of the analyzing means that if the perplexity value for the database decreases, the candidate phrase is added to the database as a superword. 11. The apparatus of claim 10, wherein the determining means determines a new perplexity value for the database using the superword.