Re: [External] The Joy of NULLs (not)

Hmmm. Wikidata can be strange.
There is a lot of indirection around.
And the redesign pages can be very misleading.
I'm not sure I see any actual blank nodes there, or at least none getting exposed.

I see ?o gets a text value in the SPARQL output - of the form "tnnnnnnn".
Whereas for a person for whom more is known about the PoB, it is a URI of a place.

If I dig further (still using the SPARQL engine, the underlying real RDF may be different again!):
wd:Q8747           p:P19        ?o   .
gives
http://www.wikidata.org/entity/statement/Q8747-49454632-42cf-dca0-2ec4-47ece3472edf
which doesn't look like a blank node to me.
And in fact
wds:Q8747-49454632-42cf-dca0-2ec4-47ece3472edf ?p ?o .
leads you to "t517245985" via ps:P19

So, clearly the ISBLANK does something, so internally it is probably doing what you say, but that is not being exposed.


Cheers

> On 12 Aug 2019, at 15:05, Young,Jeff (OR) <jyoung@oclc.org> wrote:
> 
> Here’s an example showing blank nodes being used to declare the place of birth is unknown in Wikidata:
> 
> https://w.wiki/6$y
> 
> In the UI, it is rendered like this:
> 
> <image001.png>
> 
> Jeff
> 
> From: Daniel Hernandez <daniel@degu.cl>
> Date: Monday, August 12, 2019 at 9:42 AM
> To: "semantic-web@w3.org" <semantic-web@w3.org>
> Subject: [External] Re: The Joy of NULLs (not)
> Resent-From: <semantic-web@w3.org>
> Resent-Date: Monday, August 12, 2019 at 9:37 AM
> 
> As Enrico pointed, blank nodes can be used to represent unknown values.
> An example of this use is Wikidata. I don't know another example.
> 
> --
> Daniel
> 
> On Mon, 12 Aug 2019 07:36:41 +0000
> Franconi Enrico <franconi@inf.unibz.it> wrote:
> 
>> Mike, this could easily happen in an RDF world if you register a
>> vanity licence plate with anything starting with "_". Indeed, bnodes
>> would be the right way to represent unknown but existing plates. --e.
>> 
>> Il giorno 11 ago 2019, alle ore 23:10, Michael F Uschold
>> <uschold@gmail.com<mailto:uschold@gmail.com>> ha scritto:
>> 
>>> This is hilarious. It could never happen in an RDF world! No value,
>>> no triple.
>>> 
>>> He tried to prank the DMV. Then his vanity license plate backfired
>>> big time.
>>> https://mashable.com/article/dmv-vanity-license-plate-def-con-backfire/<http://flip.it/NIk7FD>



-- 
Hugh
023 8061 5652

Received on Tuesday, 13 August 2019 22:26:36 UTC