  To classify is to put things in meaningful groups, but the criteria for doing
so can be problematic. Study of evolution of classification includes
ontogenetic analysis of change in classification over time. We present an
empirical analysis of the UDC over the entire period of its development. We
demonstrate stability in main classes, with major change driven by 20th century
scientific developments. But we also demonstrate a vast increase in the
complexity of auxiliaries. This study illustrates an alternative to Tennis'
"scheme-versioning" method.
