STC in VOTable: Time utypes

[Francois Bonnarel]

Markus Demleitner a écrit :
> Dear VOTable and DM folks,
>
> On the issue of a common container I've received only positive
> feedback, so I'll go ahead and have the next draft include that.
>   
Oops, I forgot to comment that point this morning.
I am not really a fan.
It is OK if you have only one coordinate "block" per Coord System.
But if you have several ? What you have is all the GROUPS for the
different "blocks" (ethen tables) accumulating at the beginning of the 
document...
And then you have to repeat several times the same AstroCoordSystem.
I was happy with only a reference to the coord system in the AstroCoords
group, which is semantically the same and let each of the AstroCoords GROUP
in the corresponding TABLE or GROUP of FIELDS.

but if I am the only one to object I can live with this.

> Meanwhile, another issue has come up that I'd like to hear opinions
> on: The time utypes.  Currently, they look like this:
>
> stc:AstroCoords.Time.TimeInstant.ISOTime or
> stc:AstroCoords.Time.TimeInstant.JDTime.
>
> I've just put the following diatribe on this on the wiki page
> (http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/STCInVOTable):
>
> """
> That is bad for at least three reasons:
>
>    1. clients have a hard time figuring out what column a time or a time 
>       error or whatever is (since they need to check at least three utypes)
>    2. we have xtype in VOTable for this purpose, and having both utype 
>       and xtype specify something then requires some rules on what to 
>       do when the attribute contradict or if there is some inference 
>       between them
>    3. data models should IMHO not be concernded with serializations
>
> So -- what's to be done?
>
>    1. Keep everything as is (ugly, but probably workable; declare 
>       clashes between utype and xtype as undefined)
>    2. Elide ISO/JD/MJDTime by special rule (but that's yet another 
>       special rule, and you cannot build an STC-X tree from utypes any more)
>    3. Change STC-X (would probably take a while and might be used 
>       to clean up some other ugly spots we have here, but it's a
>       major undertaking that would seriously delay STC-in-VOTable)
>    4. ???
> """
>
> (at the very bottom).  Emboldend by the feedback to my last question,
> I thought I'd ask around again for opinions and suggestions --
> preferably on the wiki.
>
> Thanks,
>
>           Markus
>
>   


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François   Bonnarel           Observatoire Astronomique de Strasbourg
CDS (Centre de données        11, rue de l'Université
astronomiques de Strasbourg)  F--67000 Strasbourg (France)

Tel: +33-(0)3 68 85 24 11     WWW: http://cdsweb.u-strasbg.fr/people/fb.html
Fax: +33-(0)3 68 85 24 25     E-mail: francois.bonnarel at astro.unistra.fr
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