TAP questions

[Mark Taylor]

Laszlo,

I don't think Markus answered your question (5) about response formats:

On Wed, 28 Feb 2018, Dobos, László wrote:

> 5. What is the suggested way of figuring out the list of supported output
> formats? There seems to be no standard list of mime types. For example the
> gaia tap interface at "http://gaia.ari.uni-heidelberg.de/tap/ offers this
> list:
> 
>               <outputFormat>
>                             <mime>application/x-votable+xml</mime>
>                             <alias>votable</alias>
>               </outputFormat>
>               <outputFormat>
> <mime>application/x-votable+xml;serialization=BINARY2</mime>
>                             <alias>votable/b2</alias>
>               </outputFormat>
>               <outputFormat>
> <mime>application/x-votable+xml;serialization=TABLEDATA</mime>
>                             <alias>votable/td</alias>
>               </outputFormat>
>               <outputFormat>
> <mime>application/x-votable+xml;serialization=FITS</mime>
>                             <alias>votable/fits</alias>
>               </outputFormat>
>               <outputFormat>
>                             <mime>application/fits</mime>
>                             <alias>fits</alias>
>               </outputFormat>
>               <outputFormat>
>                             <mime>application/json</mime>
>                             <alias>json</alias>
>               </outputFormat>
>               <outputFormat>
>                             <mime>text/csv</mime>
>                             <alias>csv</alias>
>               </outputFormat>
>               <outputFormat>
>                             <mime>text/tab-separated-values</mime>
>                             <alias>tsv</alias>
>               </outputFormat>
>               <outputFormat>
>                             <mime>text/plain</mime>
>                             <alias>text</alias>
>               </outputFormat>
>               <outputFormat>
>                             <mime>text/html</mime>
>                             <alias>html</alias>
>               </outputFormat>
> 
> whereas other services (e.g. vizier) use different mime types and some don't
> even provide the aliases. Are the aliases standardized so I can select the
> best format based on that or I need to do some heuristics based on the mime
> type strings?

I don't believe there is a straightforward answer to the question
as posed, but the key point is that the VOTable format is the
default, and that TAP services are required to support it.  Other
formats are an optional extra, and their MIME-type labels
are not tightly constrained.

So if you are implementing a service, make sure that VOTable is
provided, and if you are consuming a service (I think this is
where your concern comes from) just omit the FORMAT/RESPONSEFORMAT
request parameter and you can assume you will get VOTable responses.

This fact is clear from section 2.3.6 of TAP 1.0:

   "If the FORMAT parameter is omitted, the default format is VOTable.
    A TAP service must support VOTable as an output format, should
    support CSV and TSV output and may support other formats."

However, the equivalent section of PR-TAP-1.1-20170830, sec 2.7.3,
says only:

   "The RESPONSEFORMAT parameter is fully described in [DALI 1.1].
    For backwards compatibility, TAP-1.1 must also accept the FORMAT
    parameter as equivalent to RESPONSEFORMAT."

As far as I can see, DALI does not say anything about VOTable being
required, and in fact in sec 2.7.3 says:

   "A concrete DAL service specification will specify any mandatory
    or optional formats as well as new formats not listed above"

So if you were looking at TAP 1.1 for implementation, I'm not surprised
you had trouble here.

ACTION:
------
I therefore believe a fix is required to TAP 1.1: sec 2.3.6 should
make it clear that VOTable support is mandatory (and possibly that
CSV is a SHOULD for compatibility with TAP 1.0), and that VOTable is
the default output format when FORMAT/RESPONSEFORMAT parameter is
not explicitly specified.

Mark

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-9288776  http://www.star.bris.ac.uk/~mbt/