[TAP] data type for column metadata

[Arnold Rots]

I think Patrick hits the nail pretty closely on the head, here.
I will not try to improve on it.

What worries me is that most of the email discussion since his
original message, 24 hours ago, was pretty unproductive but expended a
lot of resources in terms of people's time.

Roy started it off with a flame that had no bearing on the case: it
had already been answered in the first paragraph (excluding the
introductory sentence) where it says that this is all optional.
What do you not understand about the word "optional"?

Those services that do not need this level of detail (because it is
irrelevant in the context of their information or accuracy) do not
have to provide it. Those clients who do not care about it (because of
the nature of the information they are after) don't have to contend
with it, either. But at least those services and clients who
understand what they are talking about and need it, will be able to
communicate intelligently.

Patrick said it yesterday, I explained the same point last week.


The thing that scares me is that those who are clamoring for simpicity
show, at times, a lack of understanding of the issues.
I am going to scream the next time someone asserts that astronomers
want heliocentric redshifts; or put JD, MJD, and UTC in the same
category. And, in case anybody misunderstood Anita's email: MJD and JD
cannot and should not be considered units (the unit in those cases is
'd').

  - Arnold

Patrick Dowler wrote:
[ Charset UTF-8 unsupported, converting... ]
> On 2009-04-01 01:42:36 Miguel Cervi?o wrote:
> > Maybe I am a bit lost in the discusion but I am a bit afraid  about
> > the idea of STC is needed to be implemented any case.
> 
> Coordinate system metadata would be optional and in many cases not applicable. 
> 
> > I try to work with theoretical services where STC metadata have no
> > sense at all.
> 
> I recall that STC has a term RELOCATABLE which I think means that there is no 
> absolute zero point to the values; this would be suitable for simulations. It 
> can be used to describe any kind of value.
> 
> > Ok, at this moment I must to include STC metadata in theVOTables, but
> > I would
> > prefer to have protocols where STC metadata is not mandatory.
> 
> Agreed. It is not mandatory. 
> 
> The only sense that it is STC is in there at all is that we refer to the STC 
> standard (and FITS WCS papers) for the names and definitions of the labels 
> one can include to help describe the system. 
> 
> > In this sense, I would prefer what Roy points out:
> >  > The simple way is NOT to implement astronomical time in TAP!
> 
> But that's not really a plausible approach. As Anita pointed out, if we ignore 
> these details then users will see all manner of ugly situations and think the 
> VO is broken. For example, I get an image from one service and a catalog from 
> another and overplot the catalog on the image. The image WCS is in FK5/J2000 
> and the catalog is in FK4/B1950. The result is terrible. If the correct 
> metadata is there, tools can correctly display this; if they can't do the 
> transform, at least they can warn the user that the two inputs have different 
> systems. 
> 
> This is the easiest example to come up with, but there are many... for example 
> the catalog could come from SimDB and have system=RELOCATABLE. You can't 
> really do anything with that, but at least tools and users would know how to 
> or not to compare it to empirical data.
> 
> > Otherwhise, lot of theoretical services that would make use of TAP
> > (synthesis models, isocornes,
> > models in general needed to we able to perform real data analysis in
> > the VO) will be (again)
> > outside of the VO-game [except in the Theory interest group that is
> > not allowed to produce protocols).
> 
> I sincerely hope that this does not happen and welcome all input from the 
> theory side, especially if/when we make assumptions rooted in observational 
> astronomy.
> 
> -- 
> 
> Patrick Dowler
> Tel/T?l: (250) 363-0044
> Canadian Astronomy Data Centre
> National Research Council Canada
> 5071 West Saanich Road
> Victoria, BC V9E 2M7
> 
> Centre canadien de donnees astronomiques
> Conseil national de recherches Canada
> 5071, chemin West Saanich
> Victoria (C.-B.) V9E 2M7
> 
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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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