I'm interested in knowing the number of categories, or potential
categories, in some widely used controlled vocabularies (e.g. LCSH,
Dewey Decimal, etc.).  For instance, I found that MeSH has 21,973
descriptors x 82 subheadings x 2 importance flags. (Not all those
combinations are actually possible, given restrictions on subheading use,
but this gives a sense of scale.)  I'd like similar statistics for at least
two other vocabularies, accompanied by a citation to where the
statistic came from.  If the system is open ended (new categories can
be constructed freely), I'd like to know that also, along with some
sense of how many categories are actually in use.  Thanks, Dave