Hi Abhijit,
you should clarify what are the source and target fields of the derivation. Derivation is a 'function' in the mathematical sense, i.e. given the values of the source fields the values of the target fields are determined. Having all fields you mention in the key of a DSO is not modeling a derivation relationship since since key fields may have an n:m relation.
A derivation relation using a DSO is possible without an exit implementation, just use the source characteristics as key fields and the target characteristics as data fields in the DSO.
Regards,
Gregor