  By combining recent HERMES data on semi-inclusive DIS $\pi^\pm$-production
with the singlet fragmentation function $D_\Sigma^{\pi^+}$, which is well
determined from $e^+e^-$ data, we are able to extract, for the first time, the
flavoured fragmentation functions $D_u^{\pi^+}$, $D_d^{\pi^+}$ and
$D_s^{\pi^+}$ without making any assumptions about favoured and unfavoured
transitions. Whereas $D_u^{\pi^+}$ and $D_d^{\pi^+}$ are very well determined,
the accuracy of $D_s^{\pi^+}$ is limited by the uncertainty in evolving
$D_\Sigma^{\pi^+}$ from the $Z^0$ pole down to the SIDIS scale of a few
$(GeV)^2$. We discuss how the precision on $D_s^{\pi^+}$ could be improved.
Knowledge of the $D_{q=u,d,s}^{\pi^+}$ will permit the extraction of the
polarized parton densities from future polarized SIDIS asymmetry measurements.
We study the precision that can be expected in such an extraction.
