[QUANTITY] moving on

[Jonathan McDowell]

Guy,
 [Still about 2 days behind in email but will try and catch this one:]

: > <Quantity name="IsophotalDiameter" ucd="Pos.diam.isophotal">
: >  <Quantity name="Bandpass" ucd="em.bandpass">V</Quantity>
: >  <Quantity name="SurfaceBrightness" ucd="flux.sb" unit="mag/arcsec^2">24</Quantity>
: >  <Value>3.8</Value>
: > </Quantity>
: 
: When Utype was introduced to VOTable at the Strasbourg meeting, it was
: [...]

: Johnathan's [sic] structure above doesn't seem to fit this description. [...]

I guess the idea here, however lame, was that we will NOT in the near
future model all of astronomy. Yes, the ideal thing to do would be to
have an isophotal diameter class, and class software that knows how to
handle it. And I want to construct such an object model of all
astronomy. In such a model, <IsophotalDiameter> would be a subclass of
Quantity.

But in the near-term absence of such a model, we still gain
interoperability by a simple common model for data transport, which is
that IsophotalDiameter is one of many astronomical concepts which can be
manipulated by knowing that they have a value, units, accuracy, and some
bunch of associated other concepts (metadata). Yes, it's incomplete, but
it's a step forward on where we are now, and in fact has less impedance mismatch
with the existing astronomical code-base.

 - Jonathan