When it comes to deravative I know that one speaks of backwardation if the spot rate is grater the the futures rate (i.e., S_0>f_0). In this situation the long earns a positive roll yield.
However, when it comes to currency (it refer in the following to the base currency and price to base nomenclature) we speak of backwardation if the spot exchange rate is below the forwards exchange rate (i.e., S_0<F_0) and the long earns a negative rol yield.
I do not get this. It seems to me odd: S_0>f_0 vs. S_0<F_0.
Could anyone tries to explain the logic behind these?
Thanks a lot!