Hoi,
I regularly query for for instance claim[31] ie any instance of whatever...
I would also query for the existence of a date of death in a similar way.
for me a claim with a "whatever it is that says that there is no value"
would be a positive result and I would not consider it for any processing.
It is fine that RDF does whatever, it is not what we use on a day to day
basis with Wikidata. Consequently what RDF does has no practical
implication for me.
Thanks,
GerardM
On 26 April 2015 at 19:54, Markus Krötzsch <mar...@semantic-mediawiki.org>
wrote:
> Quick reply to Denny and Gerard:
>
> @Denny: I think it makes sense to treat qualifiers under a closed-world
> semantics. That is: what is not there can safely be assumed to be false. In
> this I agree with Gerard. OTOH, I don't think it hurts very much to add
> them anyway.
>
> @Gerard: Please note that the use of novalue in qualifiers does not have
> any negative effects on tools that rely on the value not being there. We do
> not encode "novalue" as a special value, so tools that search for some
> arbitrary value will never find novalues (on any level: statement,
> qualifier, reference). So, overall, it is not such a big deal if people add
> novalue qualifiers in some places. Only tool developers who create own
> query services (not based on our RDF exports) must be aware that it would
> not be a good idea to treat "novalue" like a value internally. But that's a
> very small and rather competent group :-)
>
>
> Anyway, even if we generally agree that "not stated" means "not true" on
> the level of qualifiers, there could be cases where the explicit "novalue"
> could be valuable as documentation for other human users.
>
> Regards,
>
> Markus
>
> On 26.04.2015 00:52, Denny Vrandečić wrote:
>
>> Actually I think that having "no value" for the end date qualifier
>> probably means that it has not ended yet. There is no other way to
>> express whether this information is currently merely incomplete (i.e. it
>> has ended, but no one bothered to fill it in) or not (i.e. it has not
>> ended yet). This is pretty much the same use case as for normal claims.
>>
>> Other qualifiers I could imagine where an explicit "no value" would make
>> sense is P678, I guess.
>>
>> In references it might make sense to state explicitly that the source
>> does not have an issue number or an ISSN, etc., in order for example to
>> allow cleanup of references and to mark the cases where a reference does
>> not have a given value from those cases where it is merely incomplete.
>>
>> I don't have superstrong arguments as you see (I would have much
>> stronger arguments for "unknown value"), but I would prefer not to
>> forbid "no value" in those cases explicitly, because it might be useful
>> and it is already there.
>>
>> [1] https://www.wikidata.org/wiki/Special:WhatLinksHere/Q18615010
>>
>> On Thu, Apr 23, 2015 at 1:27 PM, Stas Malyshev <smalys...@wikimedia.org
>> <mailto:smalys...@wikimedia.org>> wrote:
>>
>> Hi!
>>
>> I was lately looking into the use of novalue in wikidata, specifically
>> in qualifiers and references. While use of novalue in property values
>> is
>> pretty clear for me, not sure it is as useful in qualifiers and refs.
>>
>> Example:
>>
>> https://www.wikidata.org/wiki/Q62#P6
>>
>> As we can see, Edwin Mah Lee is the mayor of San Francisco, with end
>> date set to "novalue". I wonder how useful is this - most entries like
>> this just omit end date, and if we query this in SPARQL, for example,
>> we
>> would do something like "FILTER NOT EXISTS (?statement q:P582
>> ?enddate)". Inconsistently having novalues there makes it harder to
>> process both visually (instead of just looking for one having no end
>> date we need to look for either no end date or end date with specific
>> "novalue") and automatically. And in overwhelming majority of cases I
>> feel "novalue" and absence of value model exactly the same fact - it
>> is
>> a current event, etc. Is there any useful case for using novalue
>> there?
>>
>> Another example: https://www.wikidata.org/wiki/Q2866#P569
>>
>> Here we have reference with "stated in":"no value". I don't think I
>> understand what it means - not stated anywhere? How would we know to
>> make such claim? Is a lie? Why would we keep confirmed lies in the
>> data?
>> Does not have confirmed source that we know of? Many things do, why
>> would we have "stated in" in this particular case?
>> Summarily, it is unclear for me that novalue in references is ever
>> useful.
>>
>> To quantify this, we do not have a lot of such things: on the partial
>> dump I'm working with for WDQS (which contains at least half of the
>> DB)
>> there are 14 novalue refs and 13 properties using novalue as
>> qualifier,
>> leader being P582 with 200+ uses, and overall 422 uses. So volume-wise
>> it's not a big deal but I'd like to figure out what's the right thing
>> to
>> do here and establish some guidelines.
>>
>> Thanks,
>> --
>> Stas Malyshev
>> smalys...@wikimedia.org <mailto:smalys...@wikimedia.org>
>>
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