DataLink local_semantics optional column proposal

[Patrick Dowler]

This looks like a useful feature. Am I right in seeing this as a way to
disambiguate where there are multiple links with the same {ID,semantics}?

If that's the case/intent, does it have to completely disambiguate? Does
{ID,semantics,local_semantics} have to be unique? I'm not sure that's
necessary and don't know what we would tell providers to do if they can't
make the tuple unique...


--
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada


On Mon, 22 Aug 2022 at 23:43, Markus Demleitner <
msdemlei at ari.uni-heidelberg.de> wrote:

> Hi DAL,
>
> On Fri, Aug 12, 2022 at 09:54:27AM +0100, Mark Taylor wrote:
> > So I'd like to see an additional column to facilitate this.
> > Markus has suggested the following definition for such a column:
> >
> >    column name: local_semantics
> >    type: text
> >    UCD: meta.id.assoc
> >    description: An identifier that allows clients to associate rows from
> >       different datalink documents on the same service with each other.
> >
> [...]
> >
> > Any comments?  Assuming some agreement or lack of disagreement is
> > established here about the general idea and specifics, then if
> > at least one data provider implements this I will add code in
> > topcat to make use of it.
>
> I think it's a good thing to have that, and in my book it's fairly
> orthogonal to semantics (or any other feature we have in datalink so
> far).  Hence, I've put it into DaCHS (SVN only so far; DaCHS
> operators: if you want this, let me know and I'll make a beta
> release), and I've taught a service where this looks reasonable to
> spit out local_semantics.
>
> That's PPAKM31, a service giving narrow-band maps of HII regions in
> M31 from cubes (reference URL:
> https://dc.zah.uni-heidelberg.de/browse/ppakm31/q); the datalink
> essentially links together the maps in the various bands extracted
> from each cube, and hence the local semantics is just an (opaque)
> label with the band info.
>
> To try this, go to the TAP service at <http://dc.g-vo.org/tap> and
> execute:
>
>   select accref, imagetitle, cube_id  from ppakm31.maps
>
> In TOPCAT, you can then configure an activation action "Invoke
> Service"; the default "View Datalink Table" is fine.  When you then
> activate a row, you will see the local_semantics column already in
> non-aware TOPCATs.  Mark's proposed functionality would then let
> people say "whatever band I'm actually looking at, I always want the
> [OIII]5007 image of the field in my extra datalink window".
>
> Which, I'd say, is a highly reasonable thing to want.
>
> So... you'd totally have my support for adding this to a
> Datalink-1_2-Next page on the Wiki.
>
>           -- Markus
>
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