Hi Maarten,

    We are actively mapping to other ontologies using the exact match P2888 property. The disease ontology is one example which is actively synchronized in Wikidata using the exact match property (P2888). This property is inspired by the SKOS:exact match property. SKOS it self had more mapping properties and I think it is a good idea to introduce some of the other SKOS mapping properties in Wikidata such broad match and narrow match. 

Andra

On Sat, Sep 22, 2018 at 7:30 AM Maarten Dammers <maarten@mdammers.nl> wrote:
Hi everyone,

Last week I presented Wikidata at the Semantics conference in Vienna (
https://2018.semantics.cc/ ). One question I asked people was: What is
keeping you from using Wikidata? One of the common responses is that
it's quite hard to combine Wikidata with the rest of the semantic web.
We have our own private ontology that's a bit on an island. Most of our
triples are in our own private format and not available in a more
generic, more widely use ontology.

Let's pick an example: Claude Lussan. No clue who he is, but my bot
seems to have added some links and the item isn't too big. Our URI is
http://www.wikidata.org/entity/Q2977729 and this is equivalent of
http://viaf.org/viaf/29578396 and
http://data.bibliotheken.nl/id/thes/p173983111 . If you look at
http://www.wikidata.org/entity/Q2977729.rdf this equivalence is
represented as:
<wdtn:P214 rdf:resource="http://viaf.org/viaf/29578396"/>
<wdtn:P1006 rdf:resource="http://data.bibliotheken.nl/id/thes/p173983111"/>

Also outputting it in a more generic way would probably make using it
easier than it is right now. Last discussion about this was at
https://www.wikidata.org/wiki/Property_talk:P1921 , but no response
since June.

That's one way of linking up, but another way is using equivalent
property ( https://www.wikidata.org/wiki/Property:P1628 ) and equivalent
class ( https://www.wikidata.org/wiki/Property:P1709 ). See for example
sex or gender ( https://www.wikidata.org/wiki/Property:P21) how it's
mapped to other ontologies. This won't produce easier RDF, but some
smart downstream users have figured out some SPARQL queries. So linking
up our properties and classes to other ontologies will make using our
data easier. This is a first step. Maybe it will be used in the future
to generate more RDF, maybe not and we'll just document the SPARQL
approach properly.

The equivalent property and equivalent class are used, but not that
much. Did anyone already try a structured approach with reporting? I'm
considering parsing popular ontology descriptions and producing reports
of what is linked to what so it's easy to make missing links, but I
don't want to do double work here.

What ontologies are important because these are used a lot? Some of the
ones I came across:
* https://www.w3.org/2009/08/skos-reference/skos.html
* http://xmlns.com/foaf/spec/
* http://schema.org/
* https://creativecommons.org/ns
* http://dbpedia.org/ontology/
* http://vocab.org/open/
Any suggestions?

Maarten


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