VO-DML specification document

[Gerard Lemson]

Dear Francois.
Markus has given a very thorough response to the main point you were trying
to make (I think).
But that point was not about the VO-DML specification document. I will try
to respond to the points you make that relate to that.
 
> Starting from the last TCG teleconf time and from that email from 
> Gerard below there has been  a lot of discussions around VO-DML those 
> days and there are some aspects which give me some concerns:
> 
> 
> *	    I think many people are still mixing two aspects which were to
be
> separated in two different drafts according to the conclusions of our 
> controversal discussion held in Hawai as they were summurized by Jesus
here:
> 
>http://wiki.ivoa.net/internal/IVOA/PlenarySessionsSep2013/DM_Closing_Hawaii
2013_JSalgado.pdf (slide 6 and 7)
> 
Sadly (for other reasons that missing a controversial discussion) I was not
in Hawaii, but the aspects you talk about were already separated into two
different documents by the time of the Heidelberg interop. This had been
announced before that meeting.
It was a decision made near the end of the utype tiger team that it would be
best to create 2 documents, one for the data modelling language, one for its
use in annotating tabular data sets using utypes, the "mapping document".
See the last 4 minutes or so on
http://wiki.ivoa.net/twiki/bin/view/IVOA/UtypesTigerTeam

> 
> I see that a lot of work has been done for the update of the first 
> draft "VO-DML: A Data Modeling Language for the VO" but nothing new 
> had been done 
> about the second draft "Mapping of Complex Data Models". The title of 
> this second draft reflected the difficulties appearing in using vo-dml
description 
> to map the models into VOTable, making an extensive but seriously 
> modified usage 
> of the utype attribute. 
The title of the utypes mapping document is "UTYPEs: Portable Data Model
References".
It can be found from reference [3] in the VO-DML spec but it has been linked
to often enough elsewhere as well.
Note that even if the title of that document was "Mapping of Complex Data
Models"
(which it is not), the adjective "complex" is associated to the "data
models" object, not to the "mapping" subject. The reason why the majority of
the tiger team was in favour of the proposed mapping mechanism is because it
is remarkably simple even for more complex models, as long as those are
designed well and written in a properly designed modelling language.

> However,  I can read several sentences which show that for many people 
> nothing has changed since the time where the introduction of the draft 
> VO-DML draft was first written.
>    Here is a quotation of the abstract of the vo-dml document "VO-DML 
> a consistent modelling language or IVOA data models"
> 
> 
> 	"Arguably the most important use case for VO-DML is the UTYPE
> specification [2]
> 	which uses it to provide a translational semantics for VOTable
> annotations.
> 	These annotations allow one to explicitly describe how instances of
> types from a
> 	data model are stored in the VOTable."
> 
>   and all the introduction still emphasize that the main use case for
> VO-DML
> modelling language is utype specification in VOTABLE. It also Implies 
> that the
> VO-DML GROUP mechanism is THE (unique) way to do the mapping.
> 
>     Last but not least I see nothing like a ""Mapping of Complex Data
> Models" document in the repository.
See above for links to the doc you must be referring to.
And I still stand by these conclusions that the utype tiger team drew, but
may well have repeated it too often in the text.
And note that the utype mapping is also arguably (!) the most important use
case for this spec, because it was the direct motivation to propose VO-DML
in the first place.

>      It must be clear to everybody that apart from this, most of the
effort done
> under building a consistent modelling language for IVOA looks very
promising to
> me. Having a description language with xml serialization alllows to 
> share diagrams and models built with different modelling softwares and 
> allows to help generating interoperable documentation and code. This 
> is a real progress and I appraciate the effort done By Mark (and now 
> Arnold) to map various models in the work, done by Gerard, Omar and 
> others. For me this is core of 
> "VO-DML a consistent modelling language for IVOA data models" and this 
> is a progress.
> Probably we have things to discuss still (the utype attribute stuff  
> and the ivoa
> datatypes among others) but I see no objection in going forward along 
> this path towards recommendation
> 
Great. So let's focus on that. We want to get the wrinkles in the spec
ironed out.
As I have repeatedly pointed out, there was a whole slew of models expressed
to VO-DML by me during tiger team. This was a proof of concept and I hoped
that authors of the original models could maybe use them as a starting point
for a refactoring effort.
I included Characterisation, which you were involved in. It would be good if
you and co-authors could try to mimic the effort of Arnold and to come up
with a VO-DML representation of that model. Particularly because attempts
are made to use it in the other efforts.
 > 
> 
> *	      So let's talk about "Mapping of Complex data models"
> 
I'll comment on your points related to the utype spec in another email
though I will not be able to improve on Markus very eloquent response.
 
Cheers
Gerard