[OBSERVATION] Space-Time Coordinates - new descriptions

[Jonathan McDowell]

Dear Observation group,
 Because there's been some confusion about the STC model,
both Arnold and I have tried to write up clearer descriptions
of the model. In my version, which I have placed at
 http://hea-www.harvard.edu/~jcm/vo/docs/stc-jcm.v1.pdf
and also on the IVOA DM twiki, I have tried to put it
in the context of Observation Characterization and also included
my own questions and suggestions for changing the STC model.
Arnold will send around his document soon (Hi, Arnold!).

I'm leaving on a trip and will be out of email contact till
April 19. When I return, I will try to begin organizing our
plans for the May Interop meeting, by which time we must have
completed our Observation model. I suggest that incorporating
the STC model in our Characterization scheme will get us
significantly closer to this goal.

I've also been working on the Mappings part of the Quantity
model, and hope a document will be circulated in the next
few days on that subject.

 - Jonathan