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

[Paul Harrison]

> On 12 Feb 2026, at 21:54, Patrick Dowler via dm <dm at ivoa.net> wrote:
> 
> I haven't looked in detail at the SemanticConcept in VO-DML, but
> adding a UCD primitive type seems like the wrong approach.
> 
> In CAOM I have a re-usable VocabularyTerm class (abstract) and I
> recall that Laurent has something like that in one or more other
> models. I do plan to examine SemanticConcept and see if it is usable
> in place of this (on my todo list).
> 
> But surely we do not want to add a primitive type for every different
> vocabulary!!
> 


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)

If it is the case that the model element does not have a constant UCD then the UCD needs to be expressed as a model element itself, and that would be the use case for having a UCD primitive.

Paul.
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