ADQL 2.1: Preferred crossmatch syntax

[Mark Taylor]

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 bris.ac.uk +44-117-9288776  http://www.star.bris.ac.uk/~mbt/