ADQL XMATCH

[Arnold Rots]

AngDistance[24CP] ?
On Apr 14, 2016 2:25 PM, "Alex Szalay" <szalay at jhu.edu> wrote:

> Distance2/Distance4
>         Or
> DistanceP (for points) / DistanceC  (for coords) ?
>
>
> --Alex
>
> -----Original Message-----
> From: dal-bounces at ivoa.net [mailto:dal-bounces at ivoa.net] On Behalf Of
> Mark Taylor
> Sent: Thursday, April 14, 2016 12:46 PM
> To: dal at ivoa.net
> Subject: Re: ADQL XMATCH
>
> On Tue, 12 Apr 2016, Markus Demleitner wrote:
>
> > But DISTANCE has been chosen in the original design of ADQL, and I'm
> > an enemy of changing thing that are not technically broken for
> > essentially aesthetic reasons.  So, my vote is for keeping DISTANCE.
>
> But *if* (not decided yet) we're changing the form of it from 2-arg to
> 4-arg, that would seem like a reasonable time for a non-gratuitous change
> of the name.
>
> Which thought nudges me to think about the consequences of overloaded
> geometry functions for TAPRegExt.
>
> TAPRegExt 1.0 sec 2.3 says this about declaring geometry functions:
>
>     ivo://ivoa.net/std/TAPRegExt#features-adqlgeo
>        Each feature declares support for one of the geometry functions
>        defined by ADQL (support for these functions is in general optional
>        for ADQL implementations, though TAP imposes some constraints on
>        what combinations of support are permitted).
>
>        The signature of these functions, where supported, is fixed
>        by ADQL; the content of the form element is just the name of
>        the function.
>
>        Example:
>
>        <feature>
>          <form>CONTAINS</form>
>        </feature>
>
> but if we're talking about overloads, there is no uniquely fixed signature
> for these functions.  In other words, TAPRegExt as currently defined does
> not have enough syntax to declare selective support for overloaded standard
> geometry functions - a TAP service can't declare that it supports
> DISTANCE(POINT,POINT) but not DISTANCE(REAL,REAL,REAL,REAL).  (note this
> doesn't apply to user-defined functions, since ivo://
> ivoa.net/std/TAPRegExt#features-udf
> does require declaration of signatures).
>
> Does it matter?
>
> --
> Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
> m.b.taylor at bris.ac.uk +44-117-9288776  http://www.star.bris.ac.uk/~mbt/
>
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