TAP questions

[Dobos, László]

Hi Mark,

Thanks for the answer, this is what I ended up doing. Some clarification
about non-table (i.e. binary) serializations in the standard would also be
great, in case you want to select the less verbose representation instead of
the default votable-xml. This is where I ran into the problem.

-Laszlo

-----Original Message-----
From: Mark Taylor [mailto:m.b.taylor at bristol.ac.uk] 
Sent: Tuesday, March 6, 2018 11:57 AM
To: Dobos, László <dobos at complex.elte.hu>
Cc: dal at ivoa.net
Subject: Re: TAP questions

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/