  We present a public, open-source relational database (we name kaepora)
containing a sample of 4975 spectra of 777 Type Ia supernovae (SNe Ia). Since
we draw from many sources, we significantly improve the spectra by inspecting
these data for quality, removing galactic emission lines and cosmic rays,
generating variance spectra, and correcting for the reddening caused by both MW
and host-galaxy dust. With our database, we organize this homogenized dataset
by 56 unique categories of SN-specific and spectrum-specific metadata. With
kaepora, we produce composite spectra of subpopulations of SNe Ia and examine
how spectral features correlate with various SN properties. These composite
spectra reproduce known correlations with phase, light-curve shape, and
host-galaxy morphology. With our large dataset, we are also able to generate
fine-grained composite spectra simultaneously over both phase and light-curve
shape. The color evolution of our composite spectra is consistent with other SN
Ia template spectra, and the spectral properties of our composite spectra are
in rough agreement with these template spectra with some subtle differences. We
investigate the spectral differences of SNe Ia that occur in galaxies with
varying morphologies. Controlling for light-curve shape, which is highly
correlated with host-galaxy morphology, we find that SNe Ia residing in
late-type and early-type galaxies have similar spectral properties at multiple
epochs. However for SNe Ia in these different environments, their spectra
appear to have Ca II near-infrared triplet features that have slightly
different strengths. Although this is apparent in the composite spectra and
there is some difference in the populations as seen by individual spectra, this
difference is not large enough to indicate differences in the underlying
populations.
