Hi Nandana,
no, we haven't investigated that further - for the "why", it is hard to
examine that at scale (you could of course ask all data providers, but...).
For the non-discoverable VoIDs, there is also a methodological problem -
how would we know that they exist if we are not able to discover them?
Best,
Heiko
Am 26.08.2015 um 12:40 schrieb Nandana Mihindukulasooriya:
Hi Heiko,
Thanks a lot for the pointer to the paper.
In your experiment, were you able to get some insights on *why* data
publishers are not providing VoID descriptions when it is applicable
to do so (leaving out single FOAF documents etc.) ?
[[Approaches using proposed methods such as VoID and the provenance
vocabulary are scarcely in use (and sometimes not implemented
according to the specification), they lead to a valid SPARQL endpoint
in less than 1% of all cases.]]
Also did you find many occasions where actually a VoID description is
available, but it is not discoverable according to the VoID spec (such
as the case you mention about not having the description in the root
level but in another level). For instance,
http://dbpedia.org/void/Dataset exists but is not in
http://dbpedia.org/.well-known/void and the resources don't provide a
back-link.
Best Regards,
Nandana
On Wed, Aug 26, 2015 at 12:05 PM, Heiko Paulheim
<he...@informatik.uni-mannheim.de
<mailto:he...@informatik.uni-mannheim.de>> wrote:
Hi all,
two years ago, we conducted an empirical experiment to find out
how promising the different approaches to discover SPARQL
endpoints are. The results were rather disappointing, see [1].
Executive summary: rather than trying to find VoID descriptions
(which rarely exist), querying catalogues like datahub seems more
promising (higher recall at least, precision is lower).
Hth.
Best,
Heiko
[1] http://www.heikopaulheim.com/docs/iswc2013_poster.pdf
Am 26.08.2015 um 11:50 schrieb Nandana Mihindukulasooriya:
Thanks all for the pointers.
Yes, it seems it is quite rare in practice. I tried several hosts
that provide Linked Data resources but couldn't find ones that
provide a VoID description in .well-known/void.
I guess there is a higher technical barrier in making that
description available in the given location compared to providing
that information in the response in most cases. So probably the
pragmatic thing to do would be to include this information either
in the content or as a Link relation header using the void
properties when dereferenced.
So I can use the void:inDataset back-link mechanism [1] and point
to a VoID description that will have the necessary information
about the query endpoints.
-----
dbpedia:Sri_Lanka void:inDataset _:DBpedia .
_:DBpedia a void:Dataset;
void:sparqlEndpoint <http://dbpedia.org/sparql>;
void:uriLookupEndpoint
<http://fragments.dbpedia.org/2014/en?subject=> .
------
or
----
Link: <http://dbpedia.org/void/Dataset>;
rel="http://rdfs.org/ns/void#inDataset";
----
Best Regards,
Nandana
[1] http://www.w3.org/TR/void/#discovery-links
On Wed, Aug 26, 2015 at 11:05 AM, Miel Vander Sande
<miel.vandersa...@ugent.be <mailto:miel.vandersa...@ugent.be>> wrote:
Hi Nandana,
I guess VoID would be the best fit
In case of LDF you could use
<...> void:uriLookupEndpoint
<http://fragments.dbpedia.org/2014/en?subject=>
But wether these exists in practice? Probably not. I'd leave
it up to the dereference publisher to provide this triple in
te response, rather than doing the .well_known thing.
Best,
Miel
On 26 Aug 2015, at 10:57, Víctor Rodríguez Doncel
<vrodrig...@fi.upm.es <mailto:vrodrig...@fi.upm.es>> wrote:
>
> Well, you might try to look in this folder location:
> .well-known/void
> And possibly find a "void:sparqlEndpoint".
>
> But this would be too good to be true.
>
> Regards,
> Víctor
>
> El 26/08/2015 10:45, Nandana Mihindukulasooriya escribió:
>> Hi,
>>
>> Is there a standard or widely used way of discovering a
query endpoint (SPARQL/LDF) associated with a given Linked
Data resource?
>>
>> I know that a client can use the "follow your nose" and
related link traversal approaches such as [1], but if I
wonder if it is possible to have a hybrid approach in which
the dereferenceable Linked Data resources that optionally
advertise query endpoint(s) in a standard way so that the
clients can perform queries on related data.
>>
>> To clarify the use case a bit, when a client dereferences
a resource URI it gets a set of triples (an RDF graph) [2].
In some cases, it might be possible that the returned graph
could be a subgraph of a named graph / default graph of an
RDF dataset. The client wants to discover if a query endpoint
that exposes the relevant dataset, if one is available.
>>
>> For example, something like the following using the
"search" link relation [3].
>>
>> ------
>> HEAD /resource/Sri_Lanka
>> Host: http://dbpedia.org
>> ------
>> 200 OK
>> Link: <http://dbpedia.org/sparql>; rel="search";
type="sparql",
<http://fragments.dbpedia.org/2014/en#dataset>; rel="search";
type="ldf"
>> ... other headers ...
>> ------
>>
>> Best Regards,
>> Nandana
>>
>> [1]
http://swsa.semanticweb.org/sites/g/files/g524521/f/201507/DissertationOlafHartig_0.pdf
>> [2]
http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-rdf-graph
>> [3]
http://www.iana.org/assignments/link-relations/link-relations.xhtml
>
>
> --
> Víctor Rodríguez-Doncel
> D3205 - Ontology Engineering Group (OEG)
> Departamento de Inteligencia Artificial
> Facultad de Informática
> Universidad Politécnica de Madrid
>
> Campus de Montegancedo s/n
> Boadilla del Monte-28660 Madrid, Spain
> Tel. (+34) 91336 3672 <tel:%28%2B34%29%2091336%203672>
> Skype: vroddon3
>
>
> ---
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>
>
--
Prof. Dr. Heiko Paulheim
Data and Web Science Group
University of Mannheim
Phone:+49 621 181 2646 <tel:%2B49%20621%20181%202646>
B6, 26, Room C1.08
D-68159 Mannheim
Mail:he...@informatik.uni-mannheim.de
<mailto:he...@informatik.uni-mannheim.de>
Web:www.heikopaulheim.com <http://www.heikopaulheim.com>
--
Prof. Dr. Heiko Paulheim
Data and Web Science Group
University of Mannheim
Phone: +49 621 181 2646
B6, 26, Room C1.08
D-68159 Mannheim
Mail: he...@informatik.uni-mannheim.de
Web: www.heikopaulheim.com
