  We discuss whether the diffractive structure functions defined by current
experiments at HERA are indeed probing the partonic structure function of the
pomeron. We observe that the {\it pseudorapidity} cuts commonly employed
require that the struck parton in the pomeron be far off mass shell in sizeable
regions of parameter space. As a result an interpretation in terms of
constituent partons within the pomeron is inadequate. One may nevertheless use
a partonic description for the {\it amplitude} for virtual photon-pomeron
scattering to compute a diffractive structure function for pseudorapidity gap
events. The resulting form may have significant scaling violation.
