how to find cutout services?

[Markus Demleitner]

Hi Albert,

On Mon, Jul 08, 2019 at 06:55:41PM +0200, alberto micol wrote:
> The SODA standard §4.3 states:
> "Resources in the IVOA Registry may include SODA capabilities.
> However, in order to use such services, clients require prior
> knowledge of suitable identifiers that are usable with a registered
> SODA standard service. As a result, finding and using a SODA
> service via the registry is not expected to be a common usage
> pattern.”
> 
> Because of that many data providers might not register their
> SODA-capable services.

And why should they?

> How can then a user search for cutout services (and not just a mere
> SIA without cutout)?

Why would they want to do that?

> I tried to query for SODA in the registry, but I could not find any
> service supporting SODA (but my ability to query the registry might
> be not that advanced!).

Well, the standard_id for soda is 

ivo://ivoa.net/std/soda#sync-1.0

So, to find ivoids of SIAP services that also declare a soda
capability, you'd say

  select * from 
  rr.capability as a
  join rr.capability as b
  using (ivoid)
  where 
    a.standard_id='ivo://ivoa.net/std/soda#sync-1.0'
    and b.standard_id like 'ivo://ivoa.net/std/sia%'

The (by RegTAP standards) odd structure of the query already is a
hint that that's perhaps a bit of a more exotic thing to do.

This currently yields two services (both from me) -- I've registered
the SODA endpoints on the two services mainly as a side effect of
registering their datalink endpoints, and that in turn I've mainly
done as a demo of pubDID resolution.  So, if you want both of these
are more accident than plan.

If you look, there's a lot more SODA/SSAP stuff registered out there.
But again, that's more a DaCHS artefact than anything else.

[Registry nerds: Yes, the interfaces on these capabilities should
have a role="std" and don't yet.  That'll be fixed in the next DaCHS
release]

> Would not be better to remove that sentence in §4.3 and encourage,
> if not even require, the data providers to include the SODA
> standard ID in their SODA-capable services?

Well, the bottom line is that at least I don't really see a use case.
The only scenario I could see is that a data collection is published
by two publishers, and a client might want to choose the more
capabable of the two publications.  I'd like to see a client wanting
to do that before I accept that as a bona fide use case.

Well, and of course there's the "I'm developing such a service and
I'd like to see how others do it" use case.  But I don't think we
should encumber the Registry with that kind of thing.  I'd say the
reference implemenation section on the RFC page of a standard is a
better mechanism there (or something else curated, for that matter).

          -- Markus