  Thanks to the execution of extensive spectroscopic surveys that have covered
large fractions of the sky down to magnitudes as faint as $i \approx 19$, it
has been possible to identify several narrow-line Seyfert 1 galaxies (NLS1s)
and to investigate their properties over a large range of the electro-magnetic
spectrum. The interpretation of their nature, however, is still hampered by the
statistical uncertainties related to the way in which NLS1 candidates are
selected. In this contribution, we present a study to detect and to model
emission lines in optical spectra extracted from the Sloan Digital Sky Survey
(SDSS), adopting the most proper strategy to identify the source of line
excitation and to produce a detailed model with measurements of several
emission-line parameters. We demonstrate the application of this technique to
explore fundamental questions, such as the presence of gas and dust around the
core of AGNs and the spectral energy distribution of their ionizing radiation.
We compare the spectral properties of NLS1s with those of other type 1 active
galaxies and we summarize the potential of this approach to identify NLS1s in
present day and future spectroscopic surveys. We finally consider the
implications of multi-frequency data analysis in the debate concerning the
intrinsic nature of NLS1s.
