Classical diagrams with BOND models and observations. Photoionization models are represented by the colored symbols: the colorbar represents the variation of the escape fraction and the size of symbol is proportional to log(U). The shape either represents the variation of metallicity (first row: for the age of 1 Myr) or stellar age (second row: for the metallicity of 8.2). The observed data points (gray dots) show the SDSS galaxy sample in the restricted metallicity range, 12 + log(O/H) = 7.6 − 8.2. The plain blue lines show the ridge lines of the entire sample. Dashed lines correspond to the AGN delimitations from Kewley et al. (2001).