ivoa: DM type system

[Laurent Michel]

Hello,

Le 12/04/2017 à 11:04, Markus Demleitner a écrit :
> Hi,
>
> On Tue, Apr 11, 2017 at 06:41:46PM +0200, Laurent Michel wrote:
>> I agree with Markus, having LITERAL @dmtypes compliant with VOTable
>> datatypes would be valuable.  Unfortunately, LITERAL @dmtypes are
>> not necessarily in the ivoa name space (ivoa:xx).
>> They can refer to dataTypes defined into the model. This is the
>> case for ENUM literals e.g..
>
> Are there any other cases except ENUMs?  If not, I'd say there's no
> big incentive to introduce any complication here.  When we just use
> VOTable types:
I do not see any other cases.
Anyway, The proposal of merging both VOTable and ivoa types is fine to me
>
> (a) normal clients just mind that they can parse the thing.  For
> that, they just need the VOTable datatype (and they already have
> parsers for that)
>
> (b) validators can infer the the set of allowed values from the VO-DML
> document, because the literal's role is known from where it stands in the
> instance document, and the VO-DML states what type that role has
> (i.e., in this case the allowed literals).
There is no blocking issue here, just a piece of extra job for the parsers.

>
> -- which of course begs the question whether we can't scupper LITERAL
> again and just use PARAMs instead of them.

I'm not member of the mapping team, but it seems to me that the (good) rule was not to use VOTable elements within the <VODML> 
block to facilitate the job for parser ignoring VO-DML.

>
>> Finally, I do not think that renaming ivoa types as VOTable
>> datatypes will help that much.
>
> Well, it's certainly saving clients the trouble of having to come up
> with parsers for all the literals of the VO-DML types when they
> already have parsers for the VOTable types.  I'd say that's, if
> nothing else, a courtesy to implementors, and given they're the ones
> that eventually control takeup, that ain't so bad.
OK, this point must be taken in consideration by the authors for the next VO-DML RFC step.

Laurent

>
>         -- Markus
>

-- 
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Laurent Michel
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