For an overview of the IVOAT, and its place within the IVOA Vocabularies recommendation, see the relevant section of the specification.
Contents:
The current vocabulary has @TOTAL@ concepts, of which @TOP@ are "TopConcepts".
This content is generated from a master text file, which might conceivably be of interest to you. It happens to be in the same form as the IAU93 master file, but this isn't documented, and may change without warning. The RDF and Turtle files above are the principal product here.