SIAv2: FORMAT?

[Alberto Micol]

Many thanks François.

I think it would be useful to change the text of SIA regarding the FORMAT parameter.

SIA specifies:
"The FORMAT parameter specifies response format(s)  (the access_format column from the ObsCore [7] data model). This column describes the format of the response from the access_url (see 3.1.3<http://www.ivoa.net/documents/SIA/20151223/REC-SIA-2.0-20151223.html#bkmRefHeading200962138146524>) so the values could be data file types (e.g. application/fits) or they could be the DataLink [8] MIME type."

The initial part of the sentence mentions "response format(s)", which that greatly overlaps,
and generates confusion (at least in my mind), with the following DALI specification:
"The RESPONSEFORMAT parameter is used so the client can specify the format of the response (e.g. the output of the job)."

The SIA FORMAT and the DALI RESPONSEFORMAT are two different things, and I think that should be better clarified
in the text of the next SIA version. Could that be done?

Many thanks,
Alberto

From: François Bonnarel <francois.bonnarel at astro.unistra.fr>
Date: Monday, 11. March 2019 at 19:09
To: Alberto Micol <amicol at eso.org>, DAL mailing list <dal at ivoa.net>
Subject: Re: SIAv2: FORMAT?


Hi Alberto, all

I understand the concern, but the logic of SIAP 2.0 (I instit on .0) is that it is not forcing outputs but only selecting.**
SO interprtaion 1 ) is correct. If you ask FORMAt=jpeg and everything is in application/fits you select .... nothing.

Allowing virtual data in SIAP 2.1 (which I hope tio happen, ASAP) will change the behavior of FORMAT to force the output to be be jpeg.

My 2 cents
Cheers
François
Le 11/03/2019 à 18:56, alberto micol a écrit :
Dear DAL,
I have a question regarding the FORMAT input parameter described in SIAv2.0:
2.1.17 FORMAT
The FORMAT parameter specifies response format(s)  (the access_format column from the ObsCore [7] data model). This column describes the format of the response from the access_url (see 3.1.3<http://www.ivoa.net/documents/SIA/20151223/REC-SIA-2.0-20151223.html#bkmRefHeading200962138146524>) so the values could be data file types (e.g. application/fits) or they could be the DataLink [8] MIME type.
It is unclear to me how to read that.
I have two possibilities in mind:

1) The FORMAT input param is used to add a constraint onto the access_format, e.g.:
    ...&FORMAT=application/fits
    gets translated into a constraint like:
    SELECT ... WHERE access_format = 'application/fits
but that does not seem to have much sense, as some data providers might have decided that access_format in the ObsCore table is always the datalink mime type, delegating and delaying the specification of the correct mime type to datalink.
In such case, the result of the above query will always be an empty set.

2) a different way of reading 2.1.17 is that FORMAT determines which access_format will be used in output, that is...
if ...&FORMAT=application/fits
then the returned votable will contain:
access_format=application/fits
access_url=the URL to directly download the FITS file (and not a datalink)
while if FORMAT=application/x-votable+xml;content=datalink
then the access_format will be "application/x-votable+xml;content=datalink”
and the access_url will return the datalink link.


Could you please help me understand the 2.1.17 specification?
I would go for interpretation (2) above, but I see that some of you have implemented (1) instead...

Many thanks in advance,
Alberto



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