New UCD1+ for SIA protocol

[Doug Tody]

On Thu, 25 Mar 2004, Robert Hanisch wrote:
> I just want to add my support for Alberto's objection to instr.scale -- I
> think this could be very confusing.  The scale here is not an attribute of
> the instrument, but of the image.  Glancing quickly through the UCD-UCD1+
> mapping, however, I do not see a UCD that fits very well.

I also agree, this is the image scale not an instrument attribute.

A larger point here is that in the process of normalizing the UCDS in
SIA V1.1, we also plan to introduce UTYPE.  The recommendation for folks
writing software interfaces to interpret SIA tables will be to use UTYPE
to identify the formally defined elements of the interface.  This is very
straightforward whereas UCD is not; we can evolve UCD independently and
our interfaces will not break.  Hence it is up to the UCD folks to assign
the best UCDs for these fields, and if we have to adjust or generalize them
later we will be able do so.

In general I think UCD should be used for hard things like inference,
semantic associations, smart queries, etc.  UTYPE is much simpler and is
what we need to identify interface elements in a straightforward manner.

	- Doug