[TAP] draft 0.42 (cleanup toward 0.5)

[Douglas Tody]

Hi Mark, Pat -

I must have missed this earlier.  I am pretty sure that the
parameterized syntax is legal, although it is less commonly seen (I
have also seen this in OpenGIS for example).  The advantage is that
if we parameterize text/xml to specify the type of content in the XML
then it is still a text/xml document, and can be processed as such by
common applications such as browsers, which will typically render and
pretty print the XML, or perhaps apply a style sheet.  This is why we
use text/xml, possibly with a subformat to specify the content, in DAL
interfaces where the output is often viewed in a browser.  (In part it
is also for consistency and backwards compatibility with SCS and SIA,
but being able to directly view the output in a browser is convenient).

For actual data files not intended to be rendered by generic common
software, application/x-votable+xml is preferred.  This is what
one would use if the output is expected to be primarily viewed in a
content specific application such as Topcat or a spectra viewer tool.

Hence in an interface like SSA text/xml with a votable subformat is
used for the query response, but application/x-votable+xml is used
for the spectrum if it is returned as a VOTable.

In the case of TAP there is no such distinction and no compelling
case to go either way.  If we care about directly viewing the VOTable
XML in a browser, text/xml would be preferred.  If we are happy
to have the browser merely save the output to a file (or possibly
display it in an application if the MIME type is configured), then
the application MIME type would be preferred.

I am pretty sure we went through this same discussion in some detail
back when SSA was standardized by the way.

 	- Doug


On Fri, 15 May 2009, Patrick Dowler wrote:

> On Wednesday 29 April 2009 05:49:15 Mark Taylor wrote:
> > Sec 2.7.1 and Sec 2.9:
> >    The usual MIME type for VOTable is "application/x-votable+xml"
> >    or maybe "text/x-votable+xml", not "text/xml; content=x-votable".
> >    "content" is not listed in the text/xml MIME type registration
> >    (RFC3023) as a mandatory or optional parameter of the text/xml
> >    MIME type.  RFC3032 also explicitly considers and rejects the
> >    idea of using a parameter like this to specify XML subformats -
> >    see Appendix A.6.
> 
> 
> Which of "application/x-votable+xml" and "text/x-votable+xml" is considered
> the best choice for TAP? For IVOA services in general? Are there good
> reasons to chose one over the other?
> 
> 
> thanks,
> 
> 
> --
> 
> 
> Patrick Dowler
> Tel/Tél: (250) 363-0044
> Canadian Astronomy Data Centre
> National Research Council Canada
> 5071 West Saanich Road
> Victoria, BC V9E 2M7
> 
> 
> Centre canadien de donnees astronomiques
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>