The proposed relational model of semantic similarity differs from feature models of similarity, such as the contrast model (Tversky, 1977), in that it is defined over the set of semantic relations that exist between two words instead of the set of features for each word.
in contrast model, the similarity S(a, b) between two objects a and b is defined in terms of the features common to a and b, A ∩ B, the features that are distinctive to a, A − B, and the features that are distinctive to b, B − A.