  We describe automatic procedures for the selection of DA white dwarfs in the
Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection
of other stellar objects (e.g., metal-poor stars and carbon stars), a flexible,
robust algorithm for detection of stellar absorption and emission lines in the
digital spectra of the HES was developed. Broad band (U-B, B-V) and narrow band
(Str\"omgren c_1) colours can be derived directly from HES spectra, with
precisions of sigma(U-B)=0.092mag; sigma(B-V)=0.095mag; sigma(c_1)=0.15mag.
  We describe simulation techniques that allow to convert model or slit spectra
to HES spectra. These simulated objective-prism spectra are used to determine
quantitative selection criteria, and for the study of selection functions. We
present an atlas of simulated HES spectra of DA and DB white dwarfs.
  Our current selection algorithm is tuned to yield maximum efficiency of the
candidate sample (minimum contamination with non-DAs). DA candidates are
selected in the B-V versus U-B and c_1 versus W_\lambda(Hbeta+Hgamma+Hdelta)
parameter spaces. The contamination of the resulting sample with hot subdwarfs
is expected to be as low as ~8%, while there is essentially no contamination
with main sequence or horizontal branch stars. We estimate that with the
present set of criteria, ~80% of DAs present in the HES database are recovered.
A yet higher degree of internal completeness could be reached at the expense of
higher contamination. However, the external completeness is limited by
additional losses caused by proper motion effects and the epoch differences
between direct and spectral plates used in the HES.
