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

[Harrison Paul]

Hi, 

we should be having this conversation in public - so I have CCed the mailing list

It think that I agree that UCD is a good candidate - and have nothing much more to say about that.

The ivoa:datetime issue is more complex - it is not very well defined in the VO-DML standard exactly what this means, but my contention is that because of its name then the thing that the original authors had in mind was https://www.w3.org/TR/xmlschema11-2/#dateTime - and these are more or less ISO8601 timestamps. My proposal would be to firm up the definition of ivoa:dateTime so that it is basically an ISO8601 timestamp in the UTC timescale (note it *must* have a timezone designator) on a terrestrial reference frame- so pretty much the same as you are proposing for ISOTime, I believe

I do not see any particular problem with ivoa:jd or ivoa:mjd - although the interesting thing conceptually is are they (along with ivoa:dateTime) potentially sub-types of an abstract ivoa:timeInstant or are we just staying that they are subtypes of ivoa:real.

It is not this reason that I do not see any particular value in an ivoa:year as it cannot conceptually be a sub-type of ivoa:timeInstant.

Regards,
	Paul. 

> On 4 Feb 2026, at 13:59, Mireille Louys <mireille.louys at unistra.fr> wrote:
> 
> Dear Paul, 
> 
> I have followed the VODML discussion yesterday at the DM running meeting . 
> what is not clear to me is the status of the IVOA base types used in the template model to build new Models . 
> 
> When we issued the PhotDM 1.1 (2022)  we needed two extra types to encode 1: time instant in ISOTime , 
> and 2: ucd strings . 
> 
> so these are defined like this in the Phot-v1.vodml.xml : (https://ivoa.net/xml/VODML/Phot-v1.vodml.xml  <https://ivoa.net/xml/VODML/Phot-v1.vodml.xml>)
> 
> ----
> 
> <primitiveType>
>     <vodml-id>UCD</vodml-id>
>     <name>UCD</name>
>     <description>Specialized string type derived from ivoa:string. UCD words belong to a controlled vocabulary. They are used as semantics tags for the content of table columns . See the UCD IVOA Recommendation.
> </description>
>     <extends>
>       <vodml-ref>ivoa:string</vodml-ref>
>     </extends>
>   </primitiveType>
> 
>   <primitiveType>
>     <vodml-id>ISOTime</vodml-id>
>     <name>ISOTime</name>
>     <description>Time stamp, represented as a string. This representaion is compliant to the DALI time stamp definition : section 3.3.3 Timestamp in
> https://www.ivoa.net/documents/DALI/20170517/REC-DALI-1.1.pdf
> This class derives from the ivoa:datetime class.
> 
> It could be inserted in the ivoa: template data model for types in a next version. </description>
>     <extends>
>       <vodml-ref>ivoa:datetime</vodml-ref>
>     </extends>
>   </primitiveType>
> 
> ----
> 
> I think this would help a lot if these types would be part of the VODML basic types . 
> 
> The same situation occured with MANGO for time stamps as discussed yesterday. 
> 
> many thanks , Mireille
> 
> 
> 
> -- 
> --
> 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
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