  We demonstrate that the global properties of the ``rapidity gap'' events,
observed at HERA, can be understood based on electron-gluon scattering as the
underlying partonic process. 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. This colour singlet cluster may fragment into hadrons
independently of the proton remnant, yielding the observed gap in rapidity.
