On 06.01.2017 18:24, Thomas Douillard wrote:

Same entity can be treated both as class and individual

This is valid for OWL as well.

Yes, and since Wikidata does not feature very powerful ontological statements, you could treat this like in OWL 2 DL semantically as well, i.e., a weak approach where the "class" and the "instance" are not really identified works.

Nevertheless, using the ontology might still be challenging depending on what you want to do with it, since there are quite a few meta-levels (classes of classes of classes ...) that are not cleanly separated. When I last checked, we even had some instance-of cycles ;-) Even this is not a technical problem for the OWL semantics, but maybe for some tools and approaches.

Cheers,

Markus

2017-01-05 22:21 GMT+01:00 Stas Malyshev <smalyshev@wikimedia.org
<mailto:smalyshev@wikimedia.org>>:

    Hi!

    > The best you can get in terms of "downloading the wikidata ontology" would be to
    > download all properties and all the items representing classes. We currently
    > don't have a separate dump for these. Also, do not expect this to be a concise
    > or consistent model that can be used for reasoning. You are bound to find
    > contradictions and lose ends.

    Also, Wikidata Toolkit (https://github.com/Wikidata/Wikidata-Toolkit
    <https://github.com/Wikidata/Wikidata-Toolkit>)
    can be used to generate something like taxonomy - see e.g.
    http://tools.wmflabs.org/wikidata-exports/rdf/exports/20160801/dump_download.html
    <http://tools.wmflabs.org/wikidata-exports/rdf/exports/20160801/dump_download.html>

    But one has to be careful with it as Wikidata may not (and frequently
    does not) follow assumptions that are true for proper OWL models - there
    are no limits on what can be considered a class, a subclass, an
    instance, etc. Same entity can be treated both as class and individual,
    and there may be some weird structures, including even outright errors
    such as cycles in subclass graph, etc. And, of course, it changes all
    the time :)

    --
    Stas Malyshev
    smalyshev@wikimedia.org <mailto:smalyshev@wikimedia.org>

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