Abundance ratios S/Zn versus Zn/H in DLA systems. Symbols with error bars: measurements for the samples of DLA systems listed in Table 4; curves: predictions of the models of galactic chemical evolution presented in Sect. 4. Blue diamonds: sample used to select the models of galactic chemical evolution (first part of Table 4); red circles: molecular DLA systems (second part of Table 4); black square: DLA system with peculiar nucleosynthetic abundances (last row in Table 4). Top panel: thin, cyan curves: models that pass the  selection condition (Eq. (8)); thick, magenta curve: best-fit reference model. Bottom panel: solid, red curves: dwarf models rejected by the  selection process; black, dotted curves: Milky Way models rejected by the  selection process.