ADQL 2.1: Preferred crossmatch syntax

Mark Taylor m.b.taylor at
Fri Nov 3 22:20:32 CET 2017

On Fri, 3 Nov 2017, Markus Demleitner wrote:

> >    - Does the wording about which point goes in first/second position
> >      make sense?  Is it the right way round?  I know that different
> >      services prefer different orders (e.g. TAPVizieR vs. DaCHS).
> >      Again, I don't care which it is, but if it's the sort of thing
> >      that TAP implementations can benefit from (and I have the
> >      impression that it is) there should be an agreement.
> Here, I think we shouldn't say anything (i.e., just drop the entire
> paragraph).  These troubles are essentially an ugly implementation
> detail that hopefully will go away as libraries and planners improve
> (after all, it's the planner's job to exploit symmetries in a
> database system).  We shouldn't burden a spec text with this.

Certainly fine by me from a client point of view, and it also makes
the prescription clearer.  As I say I do recall situations when
it's made a big difference which way round coordinates are specified
for queries like this, but if data providers think it's not
necessary here, good!

Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at +44-117-9288776

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