On 28/05/14 15:56, Daniel Kinzler wrote:
Am 28.05.2014 15:05, schrieb Jean-Baptiste Pressac:
Hello,
I am reading the documentation of WikiData where I learned that new properties
could be suggested for discussion. But this means adding knew properties to
WikiData. However, is it possible to use existing RDF vocabularies
Not directly. At the moment, you would just rely on a convention saying that a
given wikibase property is equivalent to a concept from some other vocabulary.
However, we are in the process of allowing claims on properties however. Once
this is possible, you will be able to connect properties to external
identifiers, much in the way data items about people etc are cross-linked with
external identifiers.
This would allow you to model the equivalence between wikidata properties and
other vicabularied. However, the software itself would not be aware of the
equivalence, so it would not be explicit in the RDF representation of data
items. But it would be easy for an external tool that knows how to interpret
such claims on properties to build an appropriate mapping using owl:sameAs or a
similar mechanism.
Daniel is right about this mechanism (but, as I said earlier today,
owl:equivalentProperty is the way to go here, not owl:sameAs). However,
there is another important point to consider: statements in Wikidata
cannot be expressed as single triples in RDF. You need auxiliary nodes
for statements to represent qualifiers and references. For details, see
our technical report
http://korrekt.org/page/Introducing_Wikidata_to_the_Linked_Data_Web
Due to this, you cannot just take external properties and use them to
replace Wikidata properties: the RDF version of Wikidata does not have
any property that links subjects (items) and objects (values) directly.
There are several approaches to get back to single triples (mainly:
named graphs and simplified exports); see the technical report for details.
The other issue is that one has to be aware of is that we use properties
not just for the main part of a statement, but also for qualifiers and
for references. One should be clear about whether an external property
applies to all or only to some of these uses. For example, an external
property that has "Person" as its domain should never be used in a
reference, even if (maybe in an error) somebody has used the Wikidata
property in a reference.
We plan to generate the RDF dumps described in the technical report
regularly. This would be a possible place for implementing the re-use of
external vocabularies. If you are interested in this, you are welcome to
join -- basically, one could have a mechanism based on either a
hard-coded mapping (in the export code) or based on templates on
property talk pages (like constraints now).
Cheers,
Markus