Hi UCD board,
I looked again at the UCD primary concepts and tried to group them. The one I am most worried about is "spect".
time,pos,em,phot Fundamental astro concepts, fine.
obs, phys Also good basic concepts
arith a good basic tree, although "math" might be better. stat Maybe should be under arith?
src Another fundamental concept, although as usual I would argue for
a distinction between "src" (2D on the sky, results of observation) and
"object" (real 3D thing in space).
instr Fairly fundamental but one could argue should be under obs
spect I worry about spect - this is a kind of data.
If spect, why not image? I predict a few years from now
we will have to change spec and instr.image to data.spect, data.image, etc.
Despite this worry, I am willing to endorse the current list for the PR.