Ordinary expression for SIDIS cross section based on QCD factorization theorem contains only partons Distribution
and Fragmentation functions. This approximation is valid for very high energies.
I'll discuss the parton model expression for (un)polarized SIDIS cross section based on LUND String Fragmentation
Model. In this model Hadronization function appears to be spin dependent even for unpolarized hadron production
off longitudinally polarized target. This effect can be modeled using LEPTO event generator. The presence of preasymptotic
terms in cross section affect the final result on polarized strangeness. Required improvements in modern techniques of flavor
decomposition will be discussed and the example based on HERMES data will be presented.