A generalized discrete Fourier transform defined over an appropriate e
xtension ring is given that is suitable to characterize Abelian codes
over residue class integer rings Z(m). The characterization is in term
s of generalized discrete Fourier transform components taking values f
rom certain ideals of the extension ring. It is shown that the results
known for cyclic codes over Z(m), like the simple characterization of
dual and self-dual codes and the nonexistence of self-dual codes for
certain values of code parameters, extend to Abelian codes over Z(m) a
s well.