On Wed, Aug 17, 2016 at 9:48 AM, Markus Kroetzsch <
markus.kroetzsch(a)tu-dresden.de> wrote:
As Gerard said, "exact" correspondence
might be difficult in most cases,
but something slightly weaker should be ok.
Something that one should note
is that, even in cases where two things are about the same "idea", their
usage in RDF is usually different if you compare Wikidata RDF to external
RDF. For example, a class in an external RDF document might have instances
assigned via rdf:type whereas a class-like item in Wikidata has instances
assigned via a chain of properties
This is exactly why the property P2888 is based on skos:exactMatch When I
proposed the "exact match" property this issue surfaced as well [1].
skos:exactMatch provides more freedom in expressing similarity between
concepts then the related owl:sameAs
possibly with further quantifiers assigned to the middle element. So you
cannot get a simple, direct correspondence on a structural level anyway.
Actually with skos:exactMatch you can.
There are also properties "equivalent class"
(P1709), "external
superproperty" (P2235), and "external subproperty" (P2236). See
https://tools.wmflabs.org/sqid/#/browse?type=properties&datatypes=5:Url
for the list of all 34 URL-type properties. Maybe you can discover others
that are relevant for you.
The reason I proposed the exact match property was with federated queries
in mind. Other resources can have a higher level of granularity on a given
topic. Being able to reach out to these resource can have benefits. In the
past we were able to federate over for example Wikdiata and Uniprot where
the URI was composed by generating the linking URI on the fly: e.g.
BIND(IRI(CONCAT("http://purl.uniprot.org/uniprot/"rot/", ?wduniprot)) as
?uniprot)
At first we experimented with the equivalent class property. But it was
pointed out by ontologists that using the property for class equality is
problematic as is partly expressed in its W3C definition: "NOTE: The use of
owl:equivalentClass does not imply class equality". [1]
Being able to store external URIs of wikidata URIs, would enable us to
really make WIkidata central in de linked data cloud, allowing representing
more granularity then currently captured in Wikidata.
Cheers,
Andra
[1]
https://www.wikidata.org/wiki/Wikidata:Property_proposal/exact_match