We derived the conditions on certain combinations of integrals of the fragmentation functions of pion using HERMES data for the sum of the charged pion multiplicities from semi-inclusive deepinelastic scattering (SIDIS) off the deuteron target. We have chosen several FFs to study the ratios of the strange PDFs S (x) and the nonstrange PDFs Q(x, Q 2) extracted from the charged pion and kaon multiplicities. We conclude that, in the LO QCD analysis and with the D π,K Q,S (Q 2) of the FFs chosen in our study, there is inconsistency between S (x, Q 2)/Q(x, Q 2) derived from the pion and kaon multiplicity data.Finally, we demonstrate that the HERMES pion multiplicity data are unlikely to be compatible with two widely-used PDFs, namely CTEQ6L and leading order NNPDF3.0.