  Following a previous detailed study of unpolarized generalized parton
distribution functions in the non-singlet sector, and at zero values of the
skewness variable, $\zeta$, we propose a physically motivated parametrization
that is valid at $\zeta \neq 0$. Our method makes use of information from the
nucleon form factor data, from deep inelastuc scattering parton distribution
functions, and from lattice results on the Mellin moments of generalized parton
distributions. It provides, therefore, a step towards a model independent
extraction of generalized distributions from the data, alternative to the
mathematical ansatz of double distributions. Comparisons with recent
experimental data on the proton are shown.
