Spectral types were taken either from SIMBAD or from other miscellaneous sources, and thus follow various classification systems (MK, HD, etc). In the case of the MK classification system of Morgan et al. (1943), the spectral type, luminosity class, and peculiarity code are given with the following designations:
For luminosity class, the following designations are used: Ia0, Ia, Iab, Ib for supergiants, II for bright giants, III for giants, IV for sub-giants, V for dwarfs. The sub-dwarfs are either noted sd followed by the spectral type, or class VI.
Peculiarities of the spectra are noted in lower case letters (e for emission lines, m for enhanced metallic lines, n for nebulous lines, nn for very nebulous, p for peculiarity in the chemical composition, s for sharp lines, sh for the existence of a shell, v for variations in the spectrum, w for weak lines, etc). CN indicates stars with an anomaly in the cyanogen abundance.
The following signs are also used: [][ : ~: ] indicates some doubt about the determination of the spectral type or luminosity class; [ / ~: ] between two spectral types or luminosity classes indicates that the two classifications were made during the Michigan Spectral Survey; [ - ~: ] between two spectral types or luminosity classes indicates that the parameter is intermediate between those given; [ +...: ] indicates composite spectra (the second spectrum is not given). [ ... : ] indicates truncated spectra (the source catalogue gives more details on the spectra, such as peculiarities)
[]In the INCA data base, the spectral types were initially taken
from the SIMBAD data base or from the original proposal when the data
were not available in SIMBAD. The spectral types available in SIMBAD in
1985, at the time of creation of the INCA data base, were mainly taken
from the Michigan Spectral Survey (Houk & Cowley 1975; Houk 1978,
1982). Volume 4 of the MSS (Houk & Smith-Moore 1988) was made available
to the INCA Consortium in advance of publication by courtesy of N.
Houk, and integrated into the INCA data base in 1988. For variable
stars, many spectral types were taken from the Fourth Edition of the
General Catalogue of Variable Stars (GCVS, Kholopov 1985, 1987).
Furthermore, many additions and corrections were made from the various
programmes proposed for Hipparcos observation, or from individual
searches in the literature. Confidence tests were performed from a
correspondence between the spectral types and the colour index when
both 
and 
magnitudes were considered reliable,
and many resulting corrections were made either to the spectral types
or to the photometric data.
The above description does not cover all MK designations which
may be found in field 32. A more complete description, with the
criteria used for classification, can be found in the introduction to
the Michigan Spectral Survey.