Thanks Andrew but I know and see the pitfalls.
The use case is only 1 level deep and to be treated not as a Category but instead as simply something "Related" or "Relative" to the topic.
Keeping within those 2 constraints from my tests seems to work reasonably well.  Beyond those constraints... I agree, its the wild west and not something that we are interested in.


On Mon, Oct 10, 2016 at 5:20 AM Andrew Gray <andrew.gray@dunelm.org.uk> wrote:
Hi Thad,

One quick red flag - I'm not sure how familiar you are with the
category system, but automatically parsing it without sanity-checking
can very quickly lead you into a minefield. There are a substantial
number of category trees which seem reasonable at first, but rapidly
go in unexpected directions.

For example, if you start at "Category:Road transport" on enwiki and
go two categories deep, you get "Category:Parking facilities‎" - so
far, so good - but you also get "Category:The Hitchhiker's Guide to
the Galaxy", "Category:Songs about buses", and "Category:Cycling
journalists‎".

There are a few pairs of categories which contain each other directly,
and a much larger number which contain each other once you go a few
levels of subcategories deep & so go in endless loops. And, of course,
a clean category tree in French might be a mess in German, or vice
versa.

None of this is to say "don't do it", but rather "don't expect it to
be clean and tidy" :-)

Andrew.

On 7 October 2016 at 02:08, Thad Guidry <thadguidry@gmail.com> wrote:
> Thanks Stas,
>
> So, hmm...we'd have to build our own parser or something is what your saying
> ?
> Because Wikidata doesn't have those kinds of connections in its graph and
> also doesn't have a SPARQL service yet against the Wikipedia
> API:Categorymembers https://www.mediawiki.org/wiki/API:Categorymembers to
> deduce those subcategories, right ?
>
> How difficult is it for someone to create a service like the LabelService ,
> but instead using the WP Categorymembers API ?  Or do you have some other
> ideas ?
>
>
> On Thu, Oct 6, 2016 at 6:10 PM Stas Malyshev <smalyshev@wikimedia.org>
> wrote:
>>
>> Hi!
>>
>> > Can it all be done in SPARQL against some services that already expose
>> > WP subcategories given a specific category ?  Or is there an API that
>> > does this already ?  other tools that might expose WP categories ?
>>
>> I don't think subcategory relationship is not recorded in Wikidata. E.g.
>> https://www.wikidata.org/wiki/Q7361750 contains
>> https://www.wikidata.org/wiki/Q14436424 but neither have any indication
>> of that.
>> The problem I guess is that category hierarchy is different on all
>> wikis, so it's hard to have one property that expresses it on Wikidata.
>>
>> You could do through "subclass of" and "category's main topic" but not
>> sure that'd capture all. E.g.: http://tinyurl.com/h7qpcdn but that only
>> captures one subcategory, since other items don't have the same
>> hierarchy in Wikidata.
>> --
>> Stas Malyshev
>> smalyshev@wikimedia.org
>>
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--
- Andrew Gray
  andrew.gray@dunelm.org.uk

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