Datalink vocabulary

Thu Sep 11 14:09:11 CEST 2014

Markus and all, hello.

On 2014 Sep 11, at 09:15, Markus Demleitner <msdemlei at ari.uni-heidelberg.de> wrote:

> Dear DAL,
> 
> [taking the discussion from interop to DAL]
> 
> On Thu, Jul 31, 2014 at 08:54:43AM +0200, François Bonnarel wrote:
>>    Thanks to Mireille, Laurent, Norman, Pat and Sarah the datalink
>> vocabulary for semantics of the links in DataLink is now available
>> here:
>> http://www.ivoa.net/rdf/datalink/

These aren't currently working as they should:

% pwd
/checkouts/code.google.com/volute/trunk/projects/dal/DataLink/datalink-terms
% make check-dist
./check-uris.sh 
Failed: http://www.ivoa.net/rdf/datalink/core [accept:text/html]
    produced status=404, Location=
    expected status=303, Location=http://www.ivoa.net/rdf/datalink/2014-08-01/datalink-core-2014-08-01.html
Failed: http://www.ivoa.net/rdf/datalink/2014-08-01/datalink-core-2014-08-01.html
    produced status=404
    expected status=200
Failed: http://www.ivoa.net/rdf/datalink/core []
    produced status=404, Location=
    expected status=303, Location=http://www.ivoa.net/rdf/datalink/2014-08-01/datalink-core-2014-08-01.html
Failed: http://www.ivoa.net/rdf/datalink/core [accept:text/turtle]
    produced status=404, Location=
    expected status=303, Location=http://www.ivoa.net/rdf/datalink/2014-08-01/datalink-core-2014-08-01.ttl
Failed: http://www.ivoa.net/rdf/datalink/2014-08-01/datalink-core-2014-08-01.ttl
    produced status=404
    expected status=200
Failed: http://www.ivoa.net/rdf/datalink/core [accept:application/rdf+xml]
    produced status=404, Location=
    expected status=303, Location=http://www.ivoa.net/rdf/datalink/2014-08-01/datalink-core-2014-08-01.rdf
Failed: http://www.ivoa.net/rdf/datalink/2014-08-01/datalink-core-2014-08-01.rdf
    produced status=404
    expected status=200
Failed: http://www.ivoa.net/rdf/datalink/datalink-core-2014-08-01.tar.gz
    produced status=404
    expected status=200
Some tests failed.  Boo!
%

(this test is in volute: trunk/projects/dal/DataLink/datalink-terms/)

I suspect that the .htaccess file (in the distribution .tar.gz file) isn't installed quite correctly.  The following should produce a 303 redirection:

% curl -i http://www.ivoa.net/rdf/datalink/core
HTTP/1.1 404 Not Found
Date: Thu, 11 Sep 2014 11:12:11 GMT
Server: Apache/2.2.15 (CentOS)
Content-Length: 293
Connection: close
Content-Type: text/html; charset=iso-8859-1

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>404 Not Found</title>
</head><body>
<h1>Not Found</h1>
<p>The requested URL /rdf/datalink/core was not found on this server.</p>
<hr>
<address>Apache/2.2.15 (CentOS) Server at www.ivoa.net Port 80</address>
</body></html>
%

> One thing I notice is that the "self" thing I've advocated is missing
> (to mark up the link to the primary dataset); however, I think it is
> important, as for some of the existing datalink prototypes, access to
> the full dataset is *only* possible through datalink, and clients
> need a robust way to discover what link to use to retrieve it.

That sounds wise, and is easy to add.

> I'd also like to make the terms more self-contained, as I expect most
> clients will, at least initially, have to work on these exclusively
> rather than have our little ontology.  And of course, neither
> publishers nor users can be expected, in general, to know the model.
> So, they'd not see #preview/image, they'd just see #image, and they'd
> be confused to see what's coming back is a preview.  This, in
> particular, concerns
> 
> image (-> preview-image)
> plot  (-> preview-plot)
> proprietary (-> ? -- I'm pretty sure rather than give that publishers
>  should be encouraged to use the other categories -- after all, all
>  data conform to *some* data model; so, they should rather say "this
>  is a characterisation" than "this is in some proprietary data
>  model)

Changing #image to #preview-image would be an easy change to make (though obviously not backward-compatible, though it's obviously too early to be worried about that).

> Also, without having read the Turtle specs, I'm pretty sure the #
> shouldn't be part of the names in the TTL file; the way this is
> written would imply, I guess, that the full form of these terms would
> be http://www.ivoa.net/rdf/datalink##preview -- which we certainly don't
> want.  Norman?

You may be misremembering the URI resolution algorithm.

If you do:

    % rapper -iturtle -ontriples .../foo.ttl

you see the sequence of triples in the most unadorned form, with all URIs fully resolved.  For example the #image ones are:

<http://www.ivoa.net/rdf/datalink/core#image> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Property> .
<http://www.ivoa.net/rdf/datalink/core#image> <http://www.w3.org/2000/01/rdf-schema#subPropertyOf> <http://www.ivoa.net/rdf/datalink/core#preview> .
<http://www.ivoa.net/rdf/datalink/core#image> <http://www.w3.org/2000/01/rdf-schema#label> "Quick look image" .
<http://www.ivoa.net/rdf/datalink/core#image> <http://www.w3.org/2000/01/rdf-schema#comment> "For example, an XMM spectral preview" .

All the best,

Norman

-- 
Norman Gray  :  http://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK