ADQL XMATCH

[Marco Molinaro]

Dear all,
the idea behind the XMATCH function was a simplification over the CONTAINS
solution, as detailed by Mark and Markus, to have an easier way for the
user to have that [maybe too simplified] crossmatch.

I'm happy that the post to define point-or-coordinates raised higher level
requests for real cross-matching capabilities in ADQL (currently in TAP
services), but I don't think this (i.e. ADQL-2.1 minor revision) is the
place to bring in such discussion, consider the XMATCH function itself will
be only optional.

That said, I suppose we have to face a fork:
- we continue with the proposed XMATCH and discuss on point vs coordinates
- we drop XMATCH from ADQL-2.1 and keep on with a general discussion for a
later major ADQL revision

My vote goes for the first one, since it seemed to be quite an easy (even
if incomplete) answer to use cases. But I'll not protest if the other
direction is taken.

I also agree with Laurent's point on optional capabilities of single
services and the need for specific optimization in that case (his mail
dropped in while I was writing).

Cheers,
    Marco

PS - for the second option above I kindly suggest to link something in
http://wiki.ivoa.net/twiki/bin/view/IVOA/ADQL or
http://wiki.ivoa.net/twiki/bin/view/IVOA/ADQL-2_0-Next in the meanwhile
ADQL-2.1 goes REC, after that ADQL-2_1-Next will host the proposed features.

2016-02-10 9:46 GMT+01:00 Alex Szalay <szalay at jhu.edu>:

> Then we should talk about how to simplify and minimize, but to implement
> something that is
> Both conceptually and mathematically  incorrect would be a big mistake.
>
> I am travelling in New Zealand for the next ten days, and today I happened
> to have a good
> internet, but mostly I am off-line. So this is not an ideal time for me to
> participate in an
> intense discussion.
>
> I am also cc'ing Laszlo and Tamas on the trail, in any case
>
> --Alex
>
>
> -----Original Message-----
> From: dal-bounces at ivoa.net [mailto:dal-bounces at ivoa.net] On Behalf Of
> Walter Landry
> Sent: Wednesday, February 10, 2016 3:37 AM
> To: dal at ivoa.net
> Subject: Re: ADQL XMATCH
>
> Alex Szalay <szalay at jhu.edu> wrote:
> > This is a paper we published 4 years ago about this. The service is
> > now in beta testing.  We just bought 4 dedicated servers.
> >
> > http://arxiv.org/pdf/1206.5021v1.pdf
>
> This is interesting work.  However, I would wager that this would be
> overkill for most of our users, who would be fine with a simple closest
> match.  For the rest, it would be insufficient, because they want to use
> error ellipses or filters on object type
>
>   http://arxiv.org/abs/1503.01184v1
>
> So I would be wary of standardizing anything too sophisticated.
>
> Cheers,
> Walter Landry
>
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