IVOA Recommendation: The UCD1+ controlled vocabulary Version 1.23
  This document describes the list of controlled terms used to build the Unified Content Descriptors, Version 1+ (UCD1+). The document describing the UCD1+ can be found at the URL: http://www.ivoa.net/Documents/latest/UCD.html. This document reviews the structure of the UCD1+ and presents the current vocabulary. 
Andrea Preite Martinez, Sebastien Derriere, Nausicaa Delmotte, Norman   Gray, Robert Mann, Jonathan McDowell, Thomas Mc Glyn...
astro-ph.IM