Semantic Distance in Conceptual Graphs

Given two concepts C1 and C2 with types T1 and T2, Garner and Tsui (1987) have proposed a modification of Sowa’s semantic distance between C1 and C2 as follows. Find the concept C3 which generalizes C1 and C2 with type T3 such that T3 is the most specific type which subsumes T1 and T2; the semantic distance between C1 and C2 is the sum of the distances from C1 to C3 and C2 to C3. It should be clear that this is indeed a metric, satisfying reflexivity, symmetry and the triangle inequality.