  Inclusive and diffractive structure functions for electron-proton scattering
are calculated in a semiclassical approach at large momentum transfer $Q^2$ and
small values of the scaling variable $x$. The basic process is the production
of a quark-antiquark pair in the colour field of the proton. The structure
functions are expressed in terms of Wilson lines along the classical
trajectories of quark and antiquark passing through the colour field, and their
covariant derivatives. Based on some rather general assumptions on properties
of the colour field, inclusive and diffractive structure functions are
evaluated in terms of four field dependent constants.
