Hi Satyam
The characteristic valuation is never done specific to one class. So the class information in the entity VALUATION would not make sense. Check the backend classification functionality: If you have a char. COLOR, assign it to two classes and assign both classes to the same material, you'll only get one COLOR in the classification screen, not one COLOR per class.
Secondly, classification is a very powerful and generic tool, which unfortunately also reflects in the naming. If you want a better understanding which backend field (table AUSP) maps to which model fields, you could have a look at the MDGM structure for char. valuation /MDGMM/_S_MM_PP_VALUATION and the labels for the data elements. You'll find that "Internal Char No." is indeed the ID of the characteristic, whereas "Internal char no." belongs to user-defined data types.
The two fields "Alternative unit" are indeed hard to hold apart...
Best regards, Ingo Bruß