Time scaing in discrete time variable?

[ratn_kumbh]

I wanted to know , if x(n) has DTFT X(e^jw)
then can we define Y(e^jw) in terms of X(e^jw)?
where Y(e^jw)is DTFT of y(n)=x(a*n)or y(n)=x(n/a). Because in these cases terms of x(n) are either missed or '0' is padded up, so i think it won't be possible to define Y(e^jw) in terms of X(e^jw). can anybody tell i m right or not?

[ratn_kumbh]

OK, i got the answer for y(n)=x(a*n), where a is an integer. Y(e^j\omega) can be defined.

it is (1/a)*\sumX(exp(j(\omega+2\pim)/a)) where m varies from 0 to a-1.

But can anybody plz tell; is it possible for y(n)=x(n/a) to define Y(e^j\omega). i am getting confused becoz of 0's which come in y(n) in this case.