Suppose the training dataset contains n compounds, which are denoted as fC 1 ,C 2 ,:::,C n g. The 11 metabolic pathway classes (cf. Table 1 ) are expressed as fP 1 ,P 2 ,:::,P 11 g, where P 1 represents the 1 st metabolic pathway class (''Carbohydrate Metabolism''), P 2 the 2 nd metabolic pathway class (''Energy Metabolism''), P 3 the 3 rd metabolic pathway class (''Lipid Metabolism''), and so forth. Thus, the descriptor of metabolic pathway classes to which the compound C i belongs to can be formulated as P(C i )~½p i,1 ,p i,2 ,:::,p i,j ,:::,p i,11 T (i~1,2,:::,n; j~1,2,::