  Let G and K be groupoids. We present the notion of a
(G_{\alpha},K_{\beta})-set and we prove a duality theorem in this context,
which extends the duality theorem for graded algebras by groups. For A a unital
G-graded algebra and X a finite split G-set, we show that there is an
isomorphism between the category of the left A-modules X-graded and the
category of the left A \#_{\alpha}^{G}X-modules. As an application of this
isomorphism, we construct a Morita context.
