Thanks for the corrections.

So https://www.wikidata.org/entity/Q42 is *the* Wikidata IRI for Douglas
Adams.  Retrieving from this IRI results in a 303 See Other to
https://www.wikidata.org/wiki/Special:EntityData/Q42, which (I guess) is the
main IRI for representations of Douglas Adams and other pages with
information about him.

>From https://www.wikidata.org/wiki/Special:EntityData/Q42 content
negotiation can be used to get the JSON representation (the default), other
representations including Turtle, and human-readable information.  (Well
actually I'm not sure that this is really correct.  It appears that instead
of directly using content negotiation, another 303 See Other is used to
provide an IRI for a document in the requested format.)

https://www.wikidata.org/wiki/Special:EntityData/Q42.json and
https://www.wikidata.org/wiki/Special:EntityData/Q42.ttl are the useful
machine-readable documents containing the Wikidata information about Douglas
Adams.  Content negotiation is not possible on these pages.

https://www.wikidata.org/wiki/Q42 is the IRI that produces a human-readable
version of the information about Douglas Adams.  Content negotiation is not
possible on this page, but it does have link rel="alternate" to the
machine-readable pages.

Strangely this page has a link rel="canonical" to itself.  Shouldn't that
link be to https://www.wikidata.org/entity/Q42?  There is a human-visible
link to this IRI, but there doesn't appear to be any machine-readable link.

RDF links to other IRIs for Douglas Adams are given in RDF pages by
properties in the wdtn namespace.  Many, but not all, identifiers are
handled this way.  (Strangely ISNI (P213) isn't even though it is linked on
the human-readable page.)

So it looks as if Wikidata can be considered as Linked Open Data but maybe
some improvements can be made.


peter



On 05/01/2018 01:03 AM, Antoine Zimmermann wrote:
> On 01/05/2018 03:25, Peter F. Patel-Schneider wrote:
>> As far as I can tell real IRIs for Wikidata are https URIs.  The http IRIs
>> redirect to https IRIs.
>
> That's right.
>
>>   As far as I can tell no content negotiation is
>> done.
>
> No, you're mistaken. Your tried the URL of a wikipage in your curl command.
> Those are for human consumption, thus not available in turtle.
>
> The "real IRIs" of Wikidata entities are like this:
> https://www.wikidata.org/entity/Q{NUMBER}
>
> However, they 303 redirect to
> https://www.wikidata.org/wiki/Special:EntityData/Q{NUMBER}
>
> which is the identifier of a schema:Dataset. Then, if you HTTP GET these
> URIs, you can content negotiate them to JSON
> (https://www.wikidata.org/wiki/Special:EntityData/Q{NUMBER}.json) or to
> turtle (https://www.wikidata.org/wiki/Special:EntityData/Q{NUMBER}.ttl).
>
>
> Suprisingly, there is no connection between the entity IRIs and the wikipage
> URLs. If one was given the IRI of an entity from Wikidata, and had no
> further information about how Wikidata works, they would not be able to
> retrieve HTML content about the entity.
>
>
> BTW, I'm not sure the implementation of content negotiation in Wikidata is
> correct because the server does not tell me the format of the resource to
> which it redirects (as opposed to what DBpedia does, for instance).
>
>
> --AZ


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