VODML base types : request for enhancement of the IVOA.1.0 template model

[Mireille Louys]

Hi Gerard ,

thanks for your answer .

Real type :

yes I used  the abstract 'ivoa:real ', but In my use-case , I would like 
to state "in the model" that it should be a double precision .
Currently the IVOA:Basetype model cannot tell this.
or did I miss anything?

ucd as <semantic_concept>:

the Semantics group is working on a representation of the UCD terms as a 
Vocabulary .

But a Ucd contains a concatenation of ucd terms , for which no uri are 
defined yet, like in a fully defined vocabulary.

so the best option , in the PhotDM use case, was to derive ucd from 
ivoa:string , and define it as a concatenation of members of the UCDList 
specification , which is/will be a vocabulary .

Cheers, Mireille

Le 16/02/2026 à 7:37 PM, Gerard Lemson a écrit :
>
> HI Mireille
>
> Re UCD type.
>
> I think this does not change the comment in my previous email. Thie is 
> precisely what the <<semanticconcept>> stereotype is for.
>
> Re zero point:
>
> The ivoa:real IS NOT a 32 bit float. It represents the mathematical 
> concept of a real number.
>
> Is not very explicit in the data model, but that is what is intended 
> by the “from R” in
>
> <primitiveType>
>
> <vodml-id>real</vodml-id>
>
> <name>real</name>
>
> <description>A real number (from R).</description>
>
> </primitiveType>
>
> Again, it is a serialization choice how to represent these (16,32,64 
> bit floats for example, or decimal numbers)
>
> And the same is true for integer (N or Z), rational (Q), complex (C).
>
> Cheers
>
> Gerard
>
> *From:*dm <dm-bounces at ivoa.net> *On Behalf Of *Mireille Louys via dm
> *Sent:* Monday, February 16, 2026 1:13 PM
> *To:* Data Models mailing list <dm at ivoa.net>
> *Subject:* Re: VODML base types : request for enhancement of the 
> IVOA.1.0 template model
>
> *
> **      External Email - Use Caution *
>
> Dear DM,
>
> In order to help to stabilize on a use-case , here is an example where 
> I needed to derive types from the IVOA:Basetypes .
>
> it is in the PHOTDM specification , in the VODML translation from 
> Modelio to XML.
>
> https://wiki.ivoa.net/internal/IVOA/PhotDM11RFC/Photv1_1_PR_20220520.html#UCD
>
> My understanding of IVOA BaseTypes, is that they should allow us to 
> type the attributes of the classes exposed in the model.
>
> I have derived the type UCD in PhotDM as an ivoa:string , that can be 
> interpreted as an expression defined in the UCDList specification.
>
> For the ZeroPoint class, I needed attributes expressed in double 
> precision like ZeroPoint.flux.value, 
> and ZeroPoint.referenceMagnitude.value but IVOA:Basetypes offers only 
> ivoa:real .
>
> So I wish the IVOA BaseTypes could be extended to contain the basic 
> types that are used , in VOTable serialisation and XML basic types for 
> instance.
>
> In this use-case , I undertand I stick to the initial XML oriented VO 
> formats and that documents serialized in JSON would need a mapping .
>
> I hope this helps ,
>
> Mireille
>
> Le 16/02/2026 à 11:23 AM, Markus Demleitner via dm a écrit :
>
>     Dear DM,
>
>     On Mon, Feb 16, 2026 at 09:39:55AM +0000, Paul Harrison via dm wrote:
>
>         I think that if a particular model element have a constant UCD then
>
>         it should conceptually by modelled with the SemanticConcept - but
>
>         it seems that the type of “topConcept” means that it cannot be used
>
>         to express the UCD string and there is possibly no conventional
>
>         value for the vocabularyURI for UCDs. (see
>
>         https://github.com/ivoa/vo-dml/issues/19)
>
>     First off, VO-DML predates the current vocabulary spec, and therefore
>
>     limits itself to SKOS.  That limitation should be lifted
>
>     independently of the UCD business.  I'd be happy to review the
>
>     language on vocabulary usage for VO-DML 1.1, but I'd need some
>
>     poking.  Perhaps we should even have an RDF serialisation for the
>
>     instances?
>
>     For the UCD question, however, all that iss not terribly helpful.
>
>     The reason is that UCDs have syntax.  Modelling the UCD atoms as a
>
>     proper vocabulary is probably possible, and there's even a draft PR
>
>     for that<https://github.com/ivoa-std/Vocabularies/pull/31> <https://github.com/ivoa-std/Vocabularies/pull/31>, but
>
>     you'd want ("compound") UCD words here, and RDF can't (really) do
>
>     that.
>
>     Me, I'm still skeptical that VO-DML should say a lot about UCDs
>
>     beyond mentioning that Quantity-s can be adorned with them in
>
>     sufficiently capable serialisations.  But *if* there is a strong
>
>     reason to say "this must be a valid UCD", that'll need extra logic
>
>     beyond RDF.
>
>     Thanks,
>
>                  Markus
>
> -- 
> --
> Mireille Louys, MCF (Assistant Professor)
> Centre de données Astronomiques (CDS)       Equipe Images, ICube
> Observatoire de Strasbourg                  Telecom Physique Strasbourg
> 11, rue de l' Université                    300, Bd Sebastien Brandt CS 10413
> F-67000 Strasbourg                          F-67412  Illkirch Cedex

-- 
--
Mireille Louys, MCF (Assistant Professor)
Centre de données Astronomiques (CDS)       Equipe Images, ICube
Observatoire de Strasbourg                  Telecom Physique Strasbourg
11, rue de l' Université                    300, Bd Sebastien Brandt CS 10413
F-67000 Strasbourg                          F-67412  Illkirch Cedex
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