  Semi-inclusive electron scattering provides a powerful tool with which to
study the spin and flavor distributions in the proton. Greater kinematic
coverage at the proposed Electron-Polarized Ion Collider facility will enable
the valence d/u ratio to be determined at large x through pion production. At
small x, pion production can be used to extract the d-bar/u-bar ratio,
complementing existing semi-inclusive measurements by HERMES, and Drell-Yan
data from Fermilab. Asymmetries in heavier quark flavors can also be probed by
tagging strange and charm hadrons in the final state.
