Small-$x$ DIS is described as the scattering of a partonic fluctuation of
the photon off a superposition of target color fields. Diffraction occurs
if the emerging partonic state is in a color singlet. Introducing a specific
model for the averaging over all relevant color field configurations, both
diffractive and inclusive parton distributions at some low scale $Q_0^2$
can be calculated. A conventional DGLAP analysis results in a good
description of diffractive and inclusive structure functions at higher
values of $Q^2$.