Arrays of geometries?

[Dave Morris]

Hiya,

In an earlier discussion Markus suggested using a language feature to 
indicate whether a service supported arrays.
http://mail.ivoa.net/pipermail/dal/2017-July/007736.html

     <languageFeature 
type="ivo://ivoa.net/std/TAPRegExt#features-arrays"/>

I'd like to build on that and define two features within that URI to 
indicate support for numeric and geometric arrays.

     <languageFeature 
type="ivo://ivoa.net/std/TAPRegExt#features-adql-arrays">
         <feature>
             <form>numeric</form>
         </feature>
         <feature>
             <form>geometric</form>
         </feature>
     </languageFeature>

This would enable services to declare support one or the other or both.

If this is a useful approach I'll add a section about it in the next 
draft of the ADQL specification.

-- Dave


On 2017-09-05 12:24, Markus Demleitner wrote:
> Dear DAL,
> 
> While implementing DALI 1.1 with a view to TAP 1.1, one of my test
> cases lead to the encoding of a 2-array of points to a
> 
> <FIELD datatype="float" arraysize="2x2" xtype="point"...>
> 
> This made me realise that, as far as I can see, it's unclear what
> that means by DALI.  And it leads to the more fundamental question of
> whether xtype amends the datatype -- which would support such usage
> -- or whether it amends (datatype, arraysize) -- which probably would
> outlaw things like these.
> 
> So:
> 
> Is anyone strongly in favour of such usage?  Note that another,
> perhaps more common, use case is arrays of timestamps, which *could*
> play a role in certain time series serialisations?
> 
> ...or is anyone strongly opposed to it?
> 
> Either way, I think it's one of these corner cases where we should
> somehow agree upon a policy.  Should xtype+array be allowed?
> Forbidden?  Undefined at this point?
> 
>           -- markus