http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
an introduction to the underlying theory
Ri͡abenʹkiĭ, V. S. (Viktor Solomonovich)
S.K. Godunov and V.S. Ryabenkii ; English translation by E.M. Gelbard.
Studies in mathematics and its applications ; v. 19