  A new paradigm in Sampling theory has been developed recently by Lu and Do.
In this new approach the classical linear model is replaced by a non-linear,
but structured model consisting of a union of subspaces. This is the natural
approach for the new theory of compressed sampling, representation of sparse
signals and signals with finite rate of innovation. In this article we extend
the theory of Lu and Do, for the case that the subspaces in the union are
shift-invariant spaces. We describe the subspaces by means of frame generators
instead of orthonormal bases. We show that, the one to one and stability
conditions for the sampling operator, are valid for this more general case.
