content, format, ctype, or xtype ?

[Steve Allen]

On Wed 2009-05-13T12:23:45 +0200, Alberto Micol hath writ:
> The local query engine will translate to those units.
>
> The same for times: pick up iso8601, MJD or whatever, but then stick to it.
>
> The VOTable and the entire VO should fix the units and formats of the
> things sent onto the wire.
>
> What's so incredibly wrong with this?
> Is it not up to a standard to standardise things?
> Why are we so much afraid of doing so?

The answer involves both political and technical aspects,
and the solution involves a lot of pedagogy and complexity
of implementation.

Somewhat tangentially I point out that international governments and
standards organizations have not been able to produce a pragmatic
solution for deciding on the number of seconds which have elapsed.

http://www.ucolick.org/~sla/leapsecs/epochtime.html

Even for timestamps of events in the vicinity of the surface
of the earth the practical situation looks like this

http://www.ucolick.org/~sla/leapsecs/deltat.html

Most applications simply do not care at 1e-8, but those that do
(VLBI, pulsar timing, precision radial velocity work)
require a system which handles all of the complexity seen in
those plots.

The astronomy community does not even control the meanings of the
definitions for the time scales which are practically available.
Until the rest of the world comes to a consensus, any implementation
is subject to having its underlying definitions changed.

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
UCO/Lick Observatory        Natural Sciences II, Room 165    Lat  +36.99855
University of California    Voice: +1 831 459 3046           Lng -122.06015
Santa Cruz, CA 95064        http://www.ucolick.org/~sla/     Hgt +250 m