ADQL DISTANCE argument?

[Markus Demleitner]

Hi Alberto,

On Tue, Mar 10, 2020 at 05:38:27PM +0100, alberto micol wrote:
> A standard cannot be based on what pgsphere can or cannot do.

...but a standard needs to be based on what is likely to be
implemented.  It's no good specifying behaviour that, in all
likelihood, most services will not exhibit.

> It is just only matter of allowing who can do more to do more. 
> If old implementations cannot change, well, they won’t. an error
> message will be shown; it is matter of documenting this in the
> ADQL2.1 standard.

When we know that almost all services will raise an error, we still
shouldn't promise it -- that's just bad user experience (where I give
you we already have plenty of unexpected error messages because of
incomplete or not-quite-complete implementations in the VO.  But
let's not wantonly create more).

And again, there's nothing wrong with ESO allowing a few more things
than ADQL does.  DaCHS has done that for years, and we even have
mechanisms to say that there's custom features in a concrete service.
Do that, and if it proves popular with your users, I'm sure someone
will come up and implement it in pgsphere (and other components),
too.

        -- Markus

(who has looked at the source code of various spherical geometry
database extensions and is rather wary of anything fancy they
promise...)