TAP RFC [xtype]

[Patrick Dowler]

On Monday 21 September 2009 07:19:17 Francois Ochsenbein wrote:
> I would definitvely prefer, as far as datatypes are
> concerned, simple names without a 'stc:' or 'adql:' or
> whatever prefix; after all, such definitions are also
> knwon to PQL, and 'TIMESTAMP' datatype is present everywhere.
> What matters however for POINT and REGION, is that these
> refer to the trigo sphere, and not to a usual (cartesian)
> 2-D plane.

If we do not use prefixes, then we are definitely inventing a new xtype 
vocabulary rather than just re-using names of datatypes from external 
(external to VOTable) systems. That is why people prefer the prefix, even 
though at this point we have no way to technical way to define the namespace.

> It becomes urgent to finalize this point.

Yes, it is urgent and so far we have only the existing draft as a fully 
developed option - to use ADQL datatypes:


> >TIMESTAMP: datatype="char" arraysize="*" xtype="adql:TIMESTAMP" and
> > content is in the iso8601 format, UTC only. The arraysize above is the
> > lazy way; one could specify fixed values if that was applicable (eg all
> > had only dates or all had dates and times to same precision).
This is exactly as specified in the current PR

> >REGION: datatype="char" arraysize="*" xtype="adql:REGION" and content is
> > an STC-S string.
This is exactly as specified in the current PR.

> >POINT: datatype="double" arraysize="2" xtype="adql:POINT" and content is a
> >pair of numeric values. The coordinate system is specified via a ref
> > attribute.
The current PR says datatype="char" arraysize="*" and the content would be in 
STC-S but limited to a Position in the space sub-phrase.

Above we use a pair of doubles (much more compact) but would have to require 
and document how to use ref to specify the coordinate system.


Given the lack of clear alternatives, we should just remain consistent with 
VODataServoce and use ADQL types. We just need to decide on how to specify 
POINT, so let's just vote:

(1) datatype="double" arraysize="2" xtype="adql:POINT", pair of numeric values

(2) datatype="char" arraysize="*" xtype="adql:POINT", content is STC-S 
Position

vote on list or just email me and I will tally,

-- 

Patrick Dowler
Tel/Tél: (250) 363-0044
Canadian Astronomy Data Centre
National Research Council Canada
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Centre canadien de donnees astronomiques
Conseil national de recherches Canada
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Victoria (C.-B.) V9E 2M7