On 09.01.2015 17:25, Thad Guidry wrote:
https://www.wikidata.org/wiki/Property:P279 aka "the superclass" ...
seems to have an equivalent property that refers to
http://www.w3.org/2000/01/rdf-schema#subClassOf ???
Basically yes, this was the informal design intention when the community
discussed these properties. However, we should be very careful when
stating this as an "equivalent property" to rdfs:subClassOf, since the
latter is not just some arbitrary vocabulary (like most other
properties) but part of the RDFS and OWL language definitions that come
with several possible semantics. Stating that our property is
"equivalent" to such a language feature is not the whole story.
On a related note, it might really be preferrable to use properties
"subClassOf(ExternalClass)" and "subPropertyOf(ExternalProperty)" to
relate Wikidata elements to external vocabulary. Using these properties
would mean that, from our viewpoint as a community, our claims are still
correct if we would be using certain externally defined vocabulary
elements instead of our own classes/properties.
== (Invented) Example ==
If we would have the claims
(1) Q1 P31 Q2
(2) Q2 subClassOf http://example.org/external/class/uri
then it means that we think that following claim is also meaningful:
(3) Q1 P31 http://example.org/external/class/uri
Our claim (2) tells external users that they may get instances of
http://example.org/external/class/uri from our Q2 instances.
For this application, subClassOf (and similarly subPropertyOf) is
enough. What you get with equivalentClass (equivalentProperty) is merely
the other direction.
== Example (ctnd) ==
In the example above, if we would use
(2') Q2 equivalentClass http://example.org/external/class/uri
this would mean that we think that any instance of the class
http://example.org/external/class/uri should also be in our Q2. It is a
bit like an virtual import of data that we have not even seen. I doubt
that we really want this.
The advantage of avoiding "equivalentProperty" in favour of
"subPropertyOfExternalProperty" (and similarly for classes) is also that
our definition can be more specific than the one used for the external
property/class. So we can relate our data to multiple external things,
which may fit our own definition more or less tightly.
Cheers,
Markus
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