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/[email protected]/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 Universität Dresden
+49 351 463 38486
http://korrekt.org/
