INFO tag

[Mark Taylor]

Dear Francois,

On Wed, 4 Mar 2009, Francois Ochsenbein wrote:

> >> About the <INFO> tag -- if you expect possibility of adding
> >> sub-elements (i.e. <INFO> may become a structure having
> >> for instance a LINK possibility, or even introduce
> >> a fully new sub-element) this is impossible with the
> >> VOTable1.1 definition: limiting the contents of INFO
> >> to just text locks the tag (you can't have text and
> >> sub-elements within a single XML element).
> >
> >? I don't understand that.  You certainly can have text and
> >sub-elements within a single XML element.
> 
> ==> Oh no, at least at the beginning of the XML-schemas, we had to
>     choose either simpleContents (only text) or complexType with
>     child elements. Could be not true anymore today (there is
>     a possibility of mixed='true' in complexContents elements) 
>     but it was claimed to be bad practice. Again code generators
>     would fail (I don't know if this is still true), at it makes
>     at least very difficult to define which tags are acceptable
>     within the text, therefore validation and parsing problems. 
>     I don't think this 'mixed' atrtibute has ever been used in 
>     any of the IVOA XML-schemas (I checked the schemas available
>     from the IVOA pages). Could somebody point me to such an
>     IVOA schema ?

I see; I didn't realise that by "can't have" you meant following
common practice in IVOA schemas.  Constructions like
"<p>It is a <em>nice</em> table</p>" are certainly possible in XML.
You may well be right that code generators do not like this type
of thing, and indeed that it's not good practice for XML which
is basically data-bearing rather than text-bearing.

> >> And it was felt better to do this change now
> >> than forbidding such extensions.
> >
> >felt by who?  felt why?  why not make that change in one go when
> >the additional structure is actually added rather than do half the
> >job now and (maybe) half at some unspecified point in the future?
> 
> ===> Please Mark don't be so nasty ! Obviously we do not know now
>      what will be the future needs, but I feel it is important
>      not to forbid future evolutions. This change in <INFO>
>      was decided at the Beijing meeting and presented in the
>      plenary session of conclusions on the Friday.

I'm really sorry if my comments appear abrasive.  It is absolutely 
not my wish to cause offence to anyone, but as I say I've been 
unable to see the reasoning for these changes.  My three questions 
above are genuine ones to which I've been having real trouble
finding the answers.

Since I've now made the same points more than once, and since some
others have now taken up the issue, I'll back out of this
discussion unless I have something new to say. 

> >But if the change is poorly justified or even makes things worse then
> >I don't think it should be adopted into the standard.
> >VOTable is a widely used standard within the VO.  It's already
> >become clear that the change to INFO causes complications for TAP
> >(http://www.ivoa.net/forum/dal/0902/1012.htm), and there will
> >probably be others.  If we want to make changes there should be
> >a robust justification for them.  I haven't yet seen one for this
> >case.
> >
> 
> ===> Finally you are right -- discussions take much more time
>      than adapting the code of our applications :-). But it's
>      really a surprise for me that such a debate occurs now --
>      I tried to constantly draw attention to this change
>      (at least in TAP and DAL groups)

This is not the first time I've tried to start this debate.
As I noted in my message earlier this week 
(http://www.ivoa.net/forum/votable/0903/0997.htm),
I first raised these points in October 2008
(http://www.ivoa.net/forum/votable/0810/0976.htm)
and didn't receive any response to them on that occasion.

best wishes

Mark

-- 
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/