The question of finding all
isomorphism classes of finite dimensional commutative semisimple rational algebras is
an unsolved one and is equivalent to the question of finding all number fields. We feel
that this problem may eventually be solved by the Burnside ring method, where the
number fields are related to each other in many different ways. In this note we
generalize the problem to the larger setting of G-algebras, where G is a finite abelian
group. This gives even more relations—which we investigate. In order to see what is
special about the rationals, we work as long as possible with a commutative ring
R.