12 classes

class  | biosystem code
-------+---------------
I-1    | d1*
I-2    | d2*
I-5    | d5*
II-1   | e1*
II-2   | e2*
II-5   | e5*
III-1  | f1*
III-2  | f2*
III-5  | f5*
IV-1   | g1*
IV-2   | g2*
IV-5   | g5*

(* means: all values possible)

##############################

20 classes 

class  | biosystem code
-------+---------------
I-1    | d10
I-21   | d21
I-24+  | d24,d25,d26
I-51   | d51
I-54+  | d54,d55,d56
II-1   | e10
...
