On 23.04.2015 12:25, Thomas Douillard wrote:
This is a question of point of vue and how to solves conflicted
declaration, way larger than this. There could be disputes other who is
really the father of something, this would be the same.
such a statement in Wikidata means:
* This source says that this person has no child
* This (other) source says that this person has some child
If one of the source has been proven wrong, then the statement must be
marked deprecated. If it's undecided and still disputed whose right,
then we keep the two statements. This is how Wikidata was conceptually
built By Denny, Markus, Lydia and the others.
Thoams and Lydia have already explained most of it, but for the record,
one motivation for no-value was that Freebase used to have a special
entity that was used as a value to express that there is no value. We
wanted to avoid this (because it easily leads to wrong query results) by
giving the community another option for saying this directly.
Nevertheless, novalue is used sparingly, and only in places where it
makes sense to explicitly record the absence of a value. For example,
one might want to say that a politician is not a member of any party,
but one would not add this information to every human.
Also, I don't think that no-value statements make much sense in
qualifiers, besides maybe serving as "documentation" for other users who
see this. Otherwise, it is usually assumed that qualifiers are
"complete", that is, what is not there can safely be assumed to not
hold. See my female mayor query: I just check that there is no end time
to mayorship and this works perfectly well.
In contrast, searching for all politicians that have no statement about
their political party given would return many politicians that actually
had a party but for which we simply did not enter it yet. No-value is
there to help Wikidata to work for such queries, which would otherwise
be impossible as long as Wikidata is not complete (i.e., probably
forever ;-).
Cheers,
Markus
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