Generic FIELD/PARAM metadata items in VOTable

[Baptiste Cecconi]

HI all, 

(I reply to this message, but I have read the more recent messages).

My first thought when Pierre mentioned the issue to me (I just registered on the Apps list), was the solution proposed by FX, use GROUP/PARAM to define things and refer to them in FIELD.  

However as the Semantics chair, I must admit that I like a lot the RDFa-like solution in a <META ...> element. Even if it is not yet a fully RDFa annotation, it drives us towards the right direction for wider interoperability (like, e.g., reuse of non-IVOA ontologies/vocabularies).

Anyway, thanks Markus for your last talk as a chair, and for staying around.

Cheers
Baptiste


> Le 19 mai 2023 à 15:27, Markus Demleitner <msdemlei at ari.uni-heidelberg.de> a écrit :
> 
> Hi Apps,
> 
> On Wed, May 17, 2023 at 05:07:59PM +0100, Mark Taylor wrote:
>>   (1) Allow FIELD/PARAM to contain INFO children:
>> 
>>        <FIELD name="healpix_id" datatype="int">
>>          <INFO name="healpix_order" value="8"/>
>>        </FIELD>
>> 
>>   (2) Invent a new element for this purpose, say META:
>> 
>>        <FIELD name="healpix_id" datatype="int">
>>          <META key="healpix_order" value="8"/>
>>        </FIELD>
>> 
>>   (3) Use the existing LINK element using RDF to indicate semantics:
>> 
>>        <FIELD name="healpix_id" datatype="int">
>>          <LINK action="rdf" content-role="#healpix_order" value="8"/>
>>        </FIELD>
>> 
> [...]
>> 
>> I think either of us could live with either solution.
>> Markus feel free to correct or clarify any of the above.
> 
> I think Mark has nicely summarised the state of affairs, and yes, if
> someone else does the work I won't stand in the way of either of
> these proposals.
> 
> Except... I hesitate to complicate the situation, but having somehow
> repressed the memories of that discussion, at the Bologna Interop I
> actually discussed "proper" RDF (that is, RDFa) in VOTable:
> 
> https://wiki.ivoa.net/internal/IVOA/InterOpMay2023Semantics/rdfa-notes.pdf
> 
> Given that, I'd suggest that *if* we create a new element as per
> META, let's at least make it RDFa-ready *in case* we'd ever want to
> go in that direction.  That is: literal values should go into the
> element content (if we *really* don't want that because it's not
> quite in line with the style of the rest of VOTable, then call the
> attribute @content rather than @value), and references would go into
> an @href attribute.  And we ought to use @property instead of @key.
> 
> So:
> 
>  <META property="healpix_order">8</META>
> 
> or:
> 
>  <META property="healpix_order" content="8"/>
> 
> And then perhaps, as an illustration of using an RDF object:
> 
>  <META property="https://www.ivoa.net/rdf/voresource/relationship_type#IsDerivedFrom"
>    href="ivo://cds.vizier/j/a+a/658/a167"
>> Gobrecht et al: (Al2O3)n, n=1-10, clusters data</META>
> 
> Note that that's not enough to produce the right RDF triples (because
> the subject will be wrong without doing something on the FIELD, and
> that's not pretty to do because of ID vs. id), but at least it won't
> build new barriers to RDFa in VOTable.
> 
> Given my conclusion in the talk ("it's not low-hanging fruit, and the
> fruit's not terribly sweet either"), however, I think I'd still go
> for the (totally non-RDFa but otherwise nicely RDF-spirited) option (3).
> 
>            -- Markus
> 
> (who clearly is still struggling to let go of Semantics:-)