It is indeed helpful to link the Wikidata ontologies to other ontologies, particularly ones like the DBpedia ontology and the schema.org ontology. There are already quite a few links from the Wikidata ontology to several other ontologies, using the Wikidata equivalent class and property properties. Going through and ensuring that every class and property, for example, in the DBpedia ontology or the schema.org ontology is the target of a correct (!) link would be useful. Then, as you indicate, it is not so hard to query Wikidata using the external ontology or map Wikidata information into information in the other ontology.
The Wikidata ontology is much larger (almost two million classes) and much more fine grained than most (or maybe even all) other general-purpose ontologies. This is appealing as one can be much more precise in Wikidata than in other ontologies. It does make Wikidata harder to use (correctly) because to represent an entity in Wikidata one has to select among many more alternatives.
This selection is harder than it should be. The Wikidata ontology is not well organized. The Wikidata ontology has errors in it. There is not yet a good tool for visualizing or exploring the ontology (although there are some useful tools such as https://tools.wmflabs.org/bambots/WikidataClasses.php and http://tools.wmflabs.org/wikidata-todo/tree.html).
So it is not trivial to set up good mappings from the Wikidata ontology to other ontologies. When setting up equivalences one has to be careful to select the Wikidata class or property that is actually equivalent to the external class or property as opposed to a Wikidata class or property that just happens to have a similar or the same label. One also has to be similarly careful when setting up other relationships between the Wikidata ontology and other ontologies. As well, one has to be careful to select good relationships that have well-defined meanings. (Some SKOS relationships are particuarly suspect.) I suggest using only strict generalization and specialization relationships.
So I think that an effort to completely and correctly map several external general-purpose ontologies into the Wikidata ontology would be something for the Wikidata community to support. Pick a few good external ontologies and put the needed effort into adding any missing mappings and checking the mappings that already exist. Get someone or some group to commit to keeping the mapping up to date. Announce the results and show how they are useful.
Peter F. Patel-Schneider Nuance Communications
On 9/22/18 4:28 AM, Maarten Dammers 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%22/%3E <wdtn:P1006 rdf:resource="http://data.bibliotheken.nl/id/thes/p173983111%22/%3E
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
Wikidata mailing list Wikidata@lists.wikimedia.org https://lists.wikimedia.org/mailman/listinfo/wikidata