  The similarity between observed velocity structures of Al III and singly
ionized species in damped Lyman-alpha systems (DLAs) suggests the presence of
ionized gas in the regions where most metal absorption lines are formed. A
simplified model consisting of Region 1) a plane-parallel ionization bounded
region illuminated by an internal radiation field, and Region 2) a neutral
region with a negligible metal content is considered. We calculate
photoionization equilibrium models for region 1, and constrain the ionization
parameter by the observed N(Al III)/N(Si II) column density ratio. Under these
conditions we find that ionization effects are important. If these effects are
taken into account, the element abundance ratios in DLAs are quite consistent
with those observed in Milky Way stars and in H II regions of local
low-metallicity blue compact dwarf galaxies. In particular we cannot exclude
the same primary N origin in both DLAs and metal-poor galaxies. No depletion of
heavy elements on dust grains needs to be invoked, although our models do not
exclude the presence of little depletion. Although highly simplified and
relying on the strong assumption of a significantly lower metal content in
region 2, our model appears to be supported by recent data on a local DLA and
it is not in contradiction with the current knowledge on high redshift DLAs. If
correct, it offers a clear simplification in the understanding of heavy element
abundance ratios in DLAs and their comparison with the local Universe.
