  It is demonstrated that the global properties of the rapidity gap events at
HERA can be understood based on electron-gluon scattering and a
non-perturbative mechanism of colour neutralization. Using the measured
inclusive structure function $F_2$ to determine the parameters of the parton
model, the diffractive structure function $F_2^D$ is predicted. The ratio of
diffractive and inclusive cross sections, $R_D = \sigma_D/\sigma_{incl}\simeq
1/9$, is determined by the probability of the produced quark-antiquark pair to
evolve into a colour singlet state.
