  We investigate the feasibility of constraining parton distribution functions
in the proton through a comparison with data on semi-inclusive deep-inelastic
lepton-nucleon scattering. Specifically, we reweight replicas of these
distributions according to how well they reproduce recent, very precise charged
kaon multiplicity measurements and analyze how this procedure optimizes the
determination of the sea quark densities and improves their uncertainties. The
results can help to shed new light on the long standing question on the size of
the flavor and charge symmetry breaking among quarks of radiative origin. An
iterative method is proposed and adopted to account for the inevitable
correlation with what is assumed about the parton-to-hadron fragmentation
functions in the reweighting procedure. It is shown how the fragmentation
functions can be optimized simultaneously in each step of the iteration. As a
first case study, we implement this method to analyze kaon production data.
