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Re: Wikidata, SPARQL Y0K Problem

From: Birte Glimm <birte.glimm@uni-ulm.de>
Date: Fri, 27 Mar 2015 11:05:44 +0100
Message-ID: <CABt65Oc9DOOKxuhHOHJeNVm6G3VmxZHn_utSfFRFUTLkCJwwwQ@mail.gmail.com>
To: Markus Kroetzsch <markus.kroetzsch@tu-dresden.de>
Cc: SPARQL <public-sparql-dev@w3.org>
Hi Markus,

that is great news!

Regarding the XSD issues. It is my understanding that SPARQL by
default has no understanding of datatypes, i.e., according to the spec
they are just strings (hence, "1"^^xsd:int would be different from
"1"^^xsd:int) although many implementations do interpret at least some
of the XSD datatypes.
In order to properly interpret datatypes some form of datatype
entailment as covered by the D-Entailment Regime [1] would be
required. The D-Entailment Regime explicitly refers to XSD 1.1.

Best,

Birte

[1] http://www.w3.org/TR/sparql11-entailment/#DEntRegime

On 27 March 2015 at 10:56, Markus Kroetzsch
<markus.kroetzsch@tu-dresden.de> wrote:
> Dear all, especially former members of the SPARQL WG,
>
> As you might know, the Wikimedia Foundation is currently working on setting
> up an official public SPARQL service for Wikidata. This was done not to
> integrate with RDF or to add to the semantic web, but simply because it
> seems to be the best technology for the query problem at hand. I think this
> should be considered a success :-) You are also welcome to play around with
> the preliminary test SPARQL endpoint of Wikidata, see [0], and of course to
> comment on the wikidata-l list regarding nice SPARQL queries or other ideas.
>
> However, on the way to making this a reality as a fully integrated feature
> of Wikidata/Wikipedia, there are many issues to be solved. One that came up
> recently is about xsd:date(Time) in SPARQL 1.1. As you will know, XML Schema
> has changed the semantics of its date types in incompatible ways between XSD
> 1.0 and XSD 1.1:
>
> * XSD 1.1: "-0001-02-03"^^xsd:date means "3rd Feb 2 BCE"  [1]
> * XSD 1.0: "-0001-02-03"^^xsd:date means "3rd Feb 1 BCE"  [2]
>
> Needless to say that this is a big deal in applications like Wikidata, where
> you have a lot of historical dates. The obvious question now is: What does
> "-0001-02-03"^^xsd:date mean when used in SPARQL? RDF? OWL? Here is what I
> have found so far:
>
> * RDF 1.0: year 1 BCE
> * OWL 1: year 1 BCE
> * SPARQL 1.0: year 1 BCE
> (all as expected)
>
> * RDF 1.1: year 2 BCE [3]
> * OWL 2: year 2 BCE [4]
> * SPARQL 1.1: ???
>
> It is interesting to note that the semantic changes in XSD, RDF and OWL each
> are breaking changes, which change the meaning of existing documents (where
> the document itself may not contain any hint as to whether it was created
> before or after the change).
>
> I am not sure what is the case for SPARQL 1.1. It seems very much preferable
> if SPARQL would follow the other W3C standards in this matter, but I did not
> find out yet what was the intention of the SPARQL WG. All comments are
> welcome, but in the end we are looking for a normative answer here.
>
> Best regards,
>
> Markus
>
>
> [0]
> https://www.mail-archive.com/wikidata-l@lists.wikimedia.org/msg05601.html
> (gives you the Wikidata endpoint URL, but more importantly also example
> queries for our current RDF translation, which we are currently revising in
> several places)
> [1] http://www.w3.org/TR/xmlschema11-2/#dateTime
> [2] http://www.w3.org/TR/xmlschema-2/#dateTime
> [3] http://www.w3.org/TR/rdf11-concepts/#section-Datatypes
> [4] http://www.w3.org/TR/owl2-syntax/#Datatype_Maps
>
> --
> Markus Kroetzsch
> Faculty of Computer Science
> Technische Universit├Ąt Dresden
> +49 351 463 38486
> http://korrekt.org/
>



-- 
Jun. Prof. Dr. Birte Glimm            Tel.:    +49 731 50 24125
Inst. of Artificial Intelligence         Secr:  +49 731 50 24258
University of Ulm                         Fax:   +49 731 50 24188
D-89069 Ulm                               birte.glimm@uni-ulm.de
Germany
Received on Friday, 27 March 2015 10:06:17 UTC

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