  We present an ab initio study of neutral core and valence electronic
excitations in {\alpha}-Al2O3 by solving the Bethe-Salpeter equation (BSE) of
many-body perturbation theory within an all-electron framework. Calculated
spectra at the Al K and L1 edges are in remarkable agreement with available
experiments from X-ray absorption (XAS) and X-ray Raman spectroscopy once
excitonic effects are taken into account. The combination of the BSE spectra
for the two techniques confirms the dipole-forbidden nature of the exciton
prepeak as suggested by recent calculations based on density-functional theory.
Moreover, we make predictions for resonant inelastic X-ray scattering (RIXS)
spectra at K and L1 edges, which strikingly fully overlap also beyond an
independent-particle picture. The RIXS calculations reveal two distinct regimes
as a function of incoming photon energy. Below and at the XAS threshold, we
observe Raman-like features, characterised by strong excitonic effects, which
we directly compare to peaks in the loss function. Above the XAS threshold,
instead, fluorescence features become predominant: RIXS spectra can be well
described and analyzed within an independent-particle approximation showing
similarity with the X-ray emission spectrum.
