Given a query compound, according to the information of its interactions with the 4,366 compounds in Group-I ( Table 1 ) whose metabolic pathway classes are known, the likelihood of its belonging to each of the 11 metabolic pathway classes can be easily calculated according to Eq. 4. And the scores thus obtained were sorted according to a descending order (Eq. 6) to yield the predicted metabolic pathway classes according to their different ranks or orders.