MIVOT: fully qualified attribute names

[Paul Harrison]

> On 23 Feb 2023, at 18:23, Laurent Michel <laurent.michel at astro.unistra.fr> wrote:
> 
> 
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> Laurent Michel
> SSC XMM-Newton
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> Université de Strasbourg <http://www.unistra.fr <http://www.unistra.fr/>>
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>> On 23 Feb 2023, at 18:59, Paul Harrison <paul.harrison at manchester.ac.uk <mailto:paul.harrison at manchester.ac.uk>> wrote:
>> 
>> 
>> 
>>> On 23 Feb 2023, at 14:24, Laurent Michel <laurent.michel at astro.unistra.fr <mailto:laurent.michel at astro.unistra.fr>> wrote:
>>> 
>>>>> I understand, but there is no reason but he common sense, to give a particular structure to the VOMDL-IDs. 
>>>>> We you generate VODML from XMI (modelio), you first get random IDs for the VOMDL-ID and in a second steps, there are built from [model-name, attr-name , ID of the host class], but the XSLT doing this is not part of the standard. If you edit your VOMDL by hand, like Pat did, you may introduce a distortion to this rule without breaking the schema compliance.
>>>>> 
>>>>> This is why I suggest to tell the users:
>>>>> - do not rely on names
>>>>> - do no parse VODML-IDs
>>>> 
>>>> I agree that technically the VODML-IDs are just XMLIDs andlong as they are unique within a single VODML instance that they can have any value/structure. However, this is precisely the problem, as simply regarded like this, then two instances of a VO-DML document describing a particular model could both be valid, but with entirely different sets of VODML-IDs, and in this situation another standard like MIVOT cannot use those VODML-IDs without also saying precisely which instance document is being used to describe the model. Unless there is some guarantee about the form of the VODML-ID  then there could also be undesirable behaviour that new versions of a model did not retain the exact same VODML-ID for a particular attribute.
>>>> 
>>> 
>>> I do not agree with this. Once the VODML-IDs have been set, no matter how you do it, they are part of the standard - of the VOMDL description of the model -. None is allowed to change them later on.
>>> 
>> 
>> The VO-DML standard makes no guarantee of this - it is perfectly legal for me to create the next version of the PhotDM for instance with totally different VODML-IDs. We all agree that it is sensible that a particular model element keeps a constant ID and better that it is human readable, and that the human can look at the structure of the VODML-ID and make inferences about the function of that element in the model. However, the only reason that this has happened in model instances so far is because of the XSLT processing, which you say is not part of the standard. I would like the structure that the XSLT scripts impose to be part of the standard, so that the manual edit that Pat did would actually be non-compliant.
> 
> Once your model has been reviewed and accepted, the VODML file is published on the doc repo and becomes the reference along with the spec document. 
> None can modify it anymore out of the std&doc process. 
> The VOMDL-IDs in that file are then frozen and can be used with absolute confidence.
>  Changing them is equivalent to changing the standard.
> The stability of the VOMDL-IDs is not provided by the VODML standard but by the Std&Doc rules.
> 

This is what the VO-DML standard says about VODML-IDs 

----
Identifier for the containing model element. Syntax in VO-DML/XML defined by the VODMLID type, as shown in the VO-DML/Schema snippet below. This element MUST be formatted according to the regular expression in the XML schema:

        [a-zA-Z][a-zA-Z0-9_\.]*
The value assigned to an element MUST be unique in the document and is case sensitive.

-----

I can follow all of  Std&Doc rules and all of the VO-DML std rules and produce PhotDM 1.2 with entirely different VODML-IDs - It is not sensible, but it is legal, as the standard only says that they must be unique within the document, and does not relate them to the <name> elements, so the IDs could be just random generated strings - much as happens with the XMI produced by UML modelling tools. I want to update the standard to say that it there is the structure in the VODML-IDs that many other things implicitly rely on when referring to model elements from outside the file.

I am not sure why the VO-DML standard does not address this  - possibly because as generated by the tooling the VODML-IDs look a lot like another definition of UType (https://www.ivoa.net/documents/Notes/UTypesUsage/) and it was “easier” to avoid that issue, and just treat it as a “new” way to reference data model elements. I think that was a mistake as the rigorous way that they are produced would have been the opportunity to say this is the “best” UTYPE.

Of course because the VODML-IDs are mechanically constructed it is possible to remove them….


Paul.





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