Diagram relating the metallicity 12 +log (O/H) and the gas fraction f_gas for our subsample of SFDGs. The curves represent: (red) closed-box model with oxygen yield y_O = 0.008 (0.006–0.010); (green) open box model with outflows for y_O = 0.008 (0.006–0.010) and outflow rate η = 3.2 (Sánchez Almeida et al. 2015) (2 <η< 4); (blue) open box model with outflows and inflows, choosing y_O = 0.008 (0.006–0.010), η = 3.2 and inflow rate Λ = η + 0.95. As discussed in the text, we acknowledge an average error for f_gas of ~0.2 dex.