  We explore the hypothesis that the classical and ultra-faint dwarf spheroidal
satellites of the Milky Way have been the building blocks of the Galactic halo
by comparing their [O/Fe] and [Ba/Fe] versus [Fe/H] patterns with the ones
observed in Galactic halo stars. Oxygen abundances deviate substantially from
the observed abundances in the Galactic halo stars for [Fe/H] values larger
than -2 dex, while they overlap for lower metallicities. On the other hand, for
the [Ba/Fe] ratio the discrepancy is extended at all [Fe/H] values, suggesting
that the majority of stars in the halo are likely to have been formed in situ.
Therefore, we suggest that [Ba/Fe] ratios are a better diagnostic than [O/Fe]
ratios. Moreover, we show the effects of an enriched infall of gas with the
same chemical abundances as the matter ejected and/or stripped from dwarf
satellites of the Milky Way on the chemical evolution of the Galactic halo. We
find that the resulting chemical abundances of the halo stars depend on the
assumed infall time scale, and the presence of a threshold in the gas for star
formation.
