[vo-dml] Clarification on composition rule..

[Gerard Lemson]

So we seem to agree on the use of open-ended multiplicities for *attributes* in some edge cases.
For what it's worth, in my opinion a pixel in a camera should be an objecttype, for which an ordinary composition rule is adequate.

In a previous email had some questions about the representation of polynomial and polygon.
I think ("for philosophical reasons") these are valuetypes and was wondering whether a structured string would be a useful representation iso a complex hierarchy of objects. 

As to the case that started this discussion, I am still wondering whether the issue could be resolved more elegantly once an explicit representation of the things that are being mapped/transferred is added to the model.

Cheers
Gerard


> -----Original Message-----
> From: dm-bounces at ivoa.net <dm-bounces at ivoa.net> On Behalf Of Laurent
> MICHEL
> Sent: Tuesday, March 10, 2020 11:21
> To: dm at ivoa.net
> Subject: Re: [vo-dml] Clarification on composition rule..
> 
> 
> Hello,
> 
> I follow the Pat's point of view.
> I never really get the deep justification of not using open-ended multiplicities,
> or more accurately, I've never really understood how the conflicts between this
> rule (maxOccus = -1 discouraged) and the real world (camera pixels, polynonial
> functions, polygons..) are conceptually resolved.
> Anyway, the fact that this discussion arises from time to time shows that the
> question is still relevant.
> 
> I think that using this feature is the responsibility of the modeler and the
> standard should not give more than a simple advice on this point, not a red
> flashing warning.
> We can assume that a modeler describing polygons as an open-ended array of
> coefficients won't expect to have those coefficients individually stored in a any
> DB. From another hand, if he/she want to expose those coefficients as
> individual values, he/she will use another pattern on purpose.
> 
> Laurent
> 
> Le 09/03/2020 à 15:42, Patrick Dowler a écrit :
> > As you may know, I don't let the warning from vo-dml validation about
> > open ended multiplicity bother me too much. Polynomial is another good
> > example where it greatly limits/impacts how one might model something...
> > I ran into it way back at point, circle, polygon (oops! non-fixed size).
> > I don't expect this can be feasibly made illegal in future... I expect
> > the warning/admoinishment to be softened, maybe with some good advice
> > about when such cardinality is warranted and when another pattern may
> > be a better choice.
> >
> > my 2c,
> >
> >
> > --
> > Patrick Dowler
> > Canadian Astronomy Data Centre
> > Victoria, BC, Canada
> >
> >
> > On Mon, 9 Mar 2020 at 06:05, Gerard Lemson <glemson1 at jhu.edu
> > <mailto:glemson1 at jhu.edu>> wrote:
> >
> >     HI Mark____
> >
> >     Just for now:____
> >
> >      From the vo-dml spec:____
> >
> >     “Modelers SHOULD NOT use open ended multiplicities, i.e. with
> >     maxOccurs=-1, but it is not illegal in the current version of this
> >     specification. "____
> >
> >     indicates it is not illegal to use non-fixed size data type
> >     instances. (not that I like them as you know)____
> >
> >     __ __
> >
> >     The fact that you think you need it here may be due to an
> >     incompleteness in the model as I described in my previous
> > email.____
> >
> >     It may well be that the structure of the mapping, including
> >     explicitly representation of what-is-mapped-to-what, could make the
> >     need for an explicit indication of forward vs inverse
> > redundant.____
> >
> >     So looking forward to seeing more details of the model (and I can
> >     comment on another thread).____
> >
> >     __ __
> >
> >     Cheers____
> >
> >     Gerard____
> >
> >     __ __
> >
> >     __ __
> >
> >     There are flavors which have open ended list of content____
> >
> >         Lookup table has open ended list of Entries____
> >
> >         Polynomials have open ended list of Coefficients,  to avoid
> >     individually modeling the different order of polynomial
> > functions.____
> >
> >     __ __
> >
> >     DataTypes are supposed to have fixed size.____
> >
> >     __ __
> >
> >     Mark____
> >
> 
> --
> ---- Laurent MICHEL              Tel  (33 0) 3 68 85 24 37
>       Observatoire de Strasbourg  Fax  (33 0) 3 68 85 24 32
>       11 Rue de l'Universite      Mail laurent.michel at astro.unistra.fr
>       67000 Strasbourg (France)   Web  http://astro.u-strasbg.fr/~michel
> ---