ivoa: DM type system

CresitelloDittmar, Mark mdittmar at cfa.harvard.edu
Tue Apr 11 18:14:59 CEST 2017


re: extracting the ivoa model from the vo-dml document.
  This suggestion has come up multiple times for various reasons, and I
think it has been
  generally considered a good idea, or at least not a bad idea.. but hasn't
had sufficient
  momentum to become an action item.  I think we may be there now.

  The mail you refer to, and example serialization also depend on an
addition/change to
  the ivoa model if this alternate modeling is considered the right

re: use of 'ivoa' types in annotation.
  The ivoa types model serves to provide a common type set for models.
  What goes into the LITERAL tag in the annotation is a topic for the
Mapping syntax.
  I expect the reasoning for using the ivoa type in the annotation is to
provide consistency
  when interpreting the annotation.  Regardless of the serialization
format, interpreting the
  content is the same... and based on the vo-dml ids.

  I'll let the Mapping people talk more to that though.


On Tue, Apr 11, 2017 at 9:57 AM, Markus Demleitner <
msdemlei at ari.uni-heidelberg.de> wrote:

> Dear DM,
> I feel mildly bad for bringing another issue up, in particular since
> it really concerns VO-DML, and that this late into its RFC.  But it's
> the kind of thing you notice when you start to play with stuff, and
> in this case it's also because of the new annotation scheme showcased
> by Mark in his mail
> http://mail.ivoa.net/pipermail/dm/2017-April/005519.html.  I've made
> a corresponding note on the RFC page
> http://wiki.ivoa.net/twiki/bin/view/IVOA/VODML1RFC, but since most of
> you probably won't see it there, I take the liberty of copying it
> here:
> [With Mark and Tom's proposed serialisation I] noticed that with it
> the types in the ivoa: DM that is part of the VO-DML spec become
> actually relevant outside of the lofty heights of drawing diagrams:
> VOTable writers will have to infer them for writing LITERALs.
> Only then did I realise that ivoa: really defines another type
> system. Now, DaCHS already translates between a gazillion type
> systems (among others, postgres, python, TAP, VOTable, FITS, numpy,
> XSD). Based on this, you could say it doesn't really matter.
> But another type system still is another source of bugs, impedance
> mismatch ("oh boy, what do I translate rational into?"), and
> annoyance for our users ("What, LITERAL has a dmtype attribute that's
> using something that has nothing to do with PARAM's @type?"). Is it
> really, really, really necessary that ivoa: does not just re-use the
> VOTable type system?
> Since a thorough investigation of this matter might slow down the
> RFC: How difficult would it be to pull the ivoa: DM out of VO-DML and
> have a document of its own for it? That'd also give us a bit more
> time to think about Quantity; also, I think our future selves will be
> grateful if they don't have to re-issue VO-DML itself when they just
> want to fix ivoa:...
>         -- Markus
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