Summary: data type for column metadata

[Arnold Rots]

Markus Demleitner wrote:
> Dear TAP group,
> 
> I feel compelled to chime in on some points in yesterday's discussion:
> 
> ...
> arots at head.cfa.harvard.edu, on leaving out STC of the TAP schema:
> > Mark are suggesting, is not helpful, either. It would mean that any
> > large-scale automated searching or cross-matching is ruled out from
> > the start.
> It's not.  If it's large-scale, people would be querying the registry
> anyway, and the registry already contains full STC data (coverage),
> so for them it's not necessarily a big deal to have full STC in
> another place.  Even if the registry people say STC for columns is
> outside of their scope, as Ray seems to suggest, having to query for
> an empty VOTable in addition to a TAP schema query is not
> unreasonable, I think, if people actually set out to do automated
> science.

I am indeed not assuming that the registry has detailed information on
all columns. There are problems in using STC information from the
registry for individual columns: there is no requirements that the
coverage be expressed in the same coordinate system, or it could be
AllSky with a low fillfactor; and there may be multiple coordinate
systems sprinkled among the columns.
My main issue is: one needs to be able to find out what it is in a way
that is defined in the protocol (i.e., a human reading the
documentation does not qualify).
Retrieving and interpreting and empty VOTable might be one way,
although it is rather unwieldy and laborious.
So far, we have been talking about positions and time; we haven't even
touched on Doppler velocities ;-)

  - Arnold

> 
> gerard.lemson at mpe.mpg.de:
> > specification: POINT('ICRS GEOCENTER',25.4, -20.0) etc.
> > And together with the ADQL DISTANCE and CONTAINS syntax would this not allow
> > spatial queries that in theory fulfill all your requirements?
> If the ADQL libraries actually implement some kind of automatic
> "conforming" of coordinates, yes, to some extent.  The issue is
> complicated, though, and given that (among other troubles) AFAIK
> still nobody really knows what kinds of strings are supposed to be in
> those first arguments to geometry functions, I'd hesitate to
> advertise this mechanism as a preferred solution.
> 
> I may feel differently about proper STC-S in REGION, though.  That
> could work nicely.
> 
> Cheers,
> 
>            Markus
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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