  The data archives from space and ground-based telescopes present a vast
opportunity for the astronomical community. We describe a classification
encoding system for stellar spectra designed for archival databases that
organizes the spectral data by "spectral classes." These classes are encoded
into a digital format of the form TT.tt.LL.PPPP, where TT and tt refer to
spectral type and subtype, LL to luminosity class, and PPPP to possible
spectral peculiarities. Archive centers may wish to utilize this system to
quantify classes of formerly arbitrary spectral classification strings found in
classification catalogs corresponding to datasets of pointed spectroscopic
observations in their holdings. The encoding system will also allow users to
request archived data based on spectral class ranges, thereby streamlining an
otherwise tedious data discovery process. Material in Appendix A is "normative"
(part of the defined standard). Appendices B and C are "informative," meant to
show how one data provider (MAST) has opted to handle some practical details.
