On 26/08/2015 23:35, Svavar Kjarrval wrote:
>
>
> On mið 26.ágú 2015 19:24, Joe Filceolaire wrote:
>>
>> Every other ontology mixes humans with fictional characters and with
>> groups of humans and possibly fictional humans (biblical characters
>> for instance). Wikidata has gone to a lot of trouble to try to
>> untangle these into separate classes. Anyone trying to get an
>> exhaustive list of humans and not using <instance of:human> deserves
>> everything he gets.
>>
>> P21 (sex or gender) is very explicitly specified as being usable for
>> humans and for other creatures. At the request of some languages we
>> have separate items for 'female human' and for 'female creature' (we
>> have the same for male), 'Female human' is 'subclass of:female
>> creature'. Relying on P21 to tell if something is or is not human is
>> not recommended as it will probably miss out all the humans who are
>> neither male nor female - wikidata has about a dozen other values that
>> can be used with this property.
>>
>> Father (P22) and mother (P25) can perfectly well be used for
>> non-humans and if the current constraints on these properties flag
>> this as a problem then the constraints will have to be updated. I
>> expect to see extensive pedigrees for racehorses entered in Wikidata.
>> Note that there is a proposal under consideration to replace P22 and
>> P25 with a single 'parent' property.
>>
>>
>>    Hope this helps
>>
>> Joe
>>
>>
> For me, it doesn't help. One of the purposes of Wikidata is that it
> should also be machine readable. If I were trying to, for example,
> travel recursively through the declarations to find deep common facts
> about some group of items, it would take much more work than necessary
> if I have to hunt down and code around a lot of wrongly categorised
> trees and special cases in the data structure.
>
> One other example is Stubbs, the current mayor of Talkeetna, (Q7627362)
> which happens to be a cat. The Wikidata item for Stubbs has the
> declaration P31->Q146 (cat). However, it also has the definition
> P31->Q30185 (mayor), a subclass of Q2285706 (head of government) which
> is a subclass of Q82955 (politician) and that's finally a subclass of Q5
> (human). One might suggest that since the item for Stubbs is
> specifically declared as a cat, that definition has priority (or some
> variation of that logic). The problem is that a machine cannot
> automatically understand that. Without special programming and/or a way
> to define contradictions like that in Wikidata, both facts are assumed
> to be correct. The machine might not even know that there is a
> contradiction at all so the machine, in its inferences, will assume
> Stubbs is both a human and a cat.
>
> - Svavar Kjarrval
>

There are a *lot* of problems with P279 (subclass), right across Wikidata.

These will only be corrected once people start doing searches in a
systematic way and addressing the anomalies they find.

In this case, politician (Q82955) should *not* be a subclass of human
(Q5), instead it should be a subclass of something like occupation
(Q13516667), or alternatively perhaps profession (Q28640).


My understanding is that currently there are a vast number of incorrect
subclass relationships in the project, messing up tree searches, and so
far it is something that has simply not yet been systematically addressed.

   -- James.


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