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

[Gerard Lemson]

Hi Paul
From the abstract of the vo-dml spec: “VO-DML is a conceptual modeling language that is agnostic of serializations, or physical representations”.
We do discuss possible serializations to XML/RDB in appendix B of the spec.
Even such “direct” serializations need to make decisions how to map VO-DML constructs to the serialization format as generally there is some impedance mismatch.
For example in XML how references are represented, in RDB how inheritance is dealt with, anywhere how datetime-s are mapped (which I assume should really use some STC-like stuff).
Laurent Bourges and I did a lot of work for the Simulation data model in VO-URP to make those things work. I think we one could create standard mappings from VO-DML to some serialization languages and should then deal with these issues there. Of course there is such a mapping for VOTable and it already had/s already ways to indicate something about serialization (XTYPE??).

Another reason why UCDs conceptually should not be primitive types is given on page 31:

The extent of a value type, i.e. its set of valid instances/values, is self-evident from its definition. That is, from the definition one can infer exactly which values exist in the set defined by the value type. Hence one can identify the instance by its value.

According to this, as UCDs and other vocabularies have been, are and will keep on changing, UCDs should not be considered data types on their own.

Cheers
Gerard


From: Paul Harrison <paul.harrison at manchester.ac.uk>
Sent: Monday, February 16, 2026 10:28 AM
To: Gerard Lemson <glemson1 at jhu.edu>
Cc: Markus Demleitner <msdemlei at ari.uni-heidelberg.de>; dm at ivoa.net
Subject: Re: VODML base types : request for enhancement of the IVOA.1.0 template model




On 16 Feb 2026, at 14:55, Gerard Lemson via dm <dm at ivoa.net<mailto:dm at ivoa.net>> wrote:

How the value should be expressed is I in my opinion a question of the serialization format. One thing to realize is that VO-DML is not so much about serialization as about annotation. If one annotates some serialization element (say a column in VOTable) as storing an attribute with a <<semanticconcept>> the serialization could mandate that that a URI identifying the concept should be written, but I think for a standard like VOTable one might allow the usual UCDs?


This might be at the core of why different people have slightly different views on what VO-DML can/should do - I personally am wanting to do direct serialization of my model instances into XML/JSON/RDB, so I want the ability to “tighten-up” the serialization within the VO-DML metamodel itself, rather than defer some of these decisions to another serialization format - I cannot see any reason why this “direct” serialization use need conflict with the “annotation” serialization usages. We could probably say explicitly that the “annotation” style usages (such as MIVOT) can “override” the direct serialization rules in the cases where there is a conflict.
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