[obs-tap]access_format

[Douglas Tody]

The access_format attribute has nothing to do with filenames, rather
it describes the format of the file which would be returned from the
remote archive.  This is also distinct from whether or not compression
is used in the transport protocol; it refers only to the file which
the client ultimately sees.  Rob - this does try to include support
for things like tile compression, which is just another variation on
the FITS file format.

 	- Doug



On Wed, 20 Apr 2011, Laurent Michel wrote:

> Dear all,
>
>
> I do not agree with the idea that compression must be infered from the 
> filename suffix for data files compressed after construction. The filename 
> can be, for instance, a service URL which has no reason to ends with a 
> compression suffix (e.g. 
> http://service.my.domain/getfile?compressed=yes&filname=mydata.fits).
> I'm not sure that the after-built compression must be notified in the 
> access_format column considering that this issue has been
> solved by all clients. Can't we simply consider that file.fits and 
> file.fits.gz are both fits file?
>
> Regards
> LM
>
> NOTE: I apologize if this message arrive twice on the list. I've some trouble 
> with it since I changed my Email address.
>
> On 19/04/2011 17:10, Mireille Louys wrote:
>> Dear all,
>> 
>> Here is the short text I suggest to have for access_format.
>> 
>> 4.7. Access Format (access_format)
>> The access_format column emphasizes information about the format of the 
>> data product if downloaded as a file. The values should
>> describe (in increasing detail) the overall file format as well as the 
>> structure of the data within the file.
>> This data model fields is important to evaluate for data discovery and data 
>> retrieval.
>> MIME types can be used for that in existing protocols ( like http). 
>> However, when dealing with observations as in ObsTAP
>> service, more information about the astronomical arrangement of data into 
>> predefined formats is very useful . For instance we
>> want to distinguish between various formats like aedm (ALMA) , evla, MUSE 
>> multi-extension fits files( IFU) etc?
>> Providing this information speeds up the interpretation step for client 
>> application consuming these files on one hand , and
>> improves data selection in the discovery step on the other hand.
>> Some data collection offer data sets are as multi-files and distribute them 
>> as as directory or tar format
>> Here we consider a list of possible MIME-type strings for various types of 
>> observational datasets
>> This could be extended or modified after implementation experience.
>> 
>> MIME-type Shortname Definition
>> application/fits fits
>> application/xml xml
>> application/x-votable+xml votable
>> image/fits fits.image any multidimensional
>> regularly sampled data cube, etc?
>> image/jpeg jpeg
>> application/x-aedm aedm ALMA Export Data Model
>> application/x-ms ms Radio measurement set
>> application/x-euro3D euro3D imaging spectroscopy
>> application/pdf pdf graphs stored as document: filter curve,
>> footprint, spectrum profile, etc.
>> application/dvi dvi graph
>> text/csv csv comma separated value
>> text/tsv tsv tab separate value
>> text/html html texte in HTML format
>> application/x-tar tar multiple files archive in tar format
>> application/x-directory+text dir multiple files set as text list
>> 
>> Compression may be applied at different levels:
>> ? after the data file is built
>> ? after binding a bunch of files into an archive file (like in .gzip,
>> .7zip, .gz, .tar.gz, etc.)
>> ? directly on the file content (jpeg, hcompress in fits images, 
>> multi-resolution compression (.MRC files as in MR/1 application)
>> In this case extension file name conveys the information directly on the 
>> file content.
>> No suffix means there is no compression applied.
>> Example of combined access format could be a concatenation of mime short 
>> name , with compression suffix.
>> 
>> 
>> 
>> 
>
> -- 
>
> ---- Laurent MICHEL              Tel  (33 0) 3 68 85 24 37
>     Observatoire de Strasbourg  Fax  (33 0) 3 68 85 24 32
>     11 Rue de l'Universite      Mail laurent.michel at astro.unistra.fr
>     67000 Strasbourg (France)   Web  http://astro.u-strasbg.fr/~michel
> ---
>