18. The computer program product according to claim 15 , wherein the preparation of the first feature vector further comprises preparing, for each first feature, a first weight of the first feature and the preparation of the second feature vector further comprises preparing, for each second feature, a second weight of the second feature; and the method further comprising determining whether the combination of the first feature and the second feature is added to the synonym list, using the first weight and the second weight.
18. The computer program product according to claim 15 , wherein the preparation of the first feature vector further comprises preparing, for each first feature, a first weight of the first feature and the preparation of the second feature vector further comprises preparing, for each second feature, a second weight of the second feature; and the method further comprising determining whether the combination of the first feature and the second feature is added to the synonym list, using the first weight and the second weight. 19. The computer program product according to claim 18 , further comprising changing the first weight of the first feature, the second weight of the second feature, or combination thereof.