Hoi,

When I add statements with "is a list of", the item I refer to works as a base. It and all subsequent statements are required to be the result of the result that is generated by WDQ in the background. The results are shown automatically from within Reasonator.

The hack is in having Reasonator interpret the limited expressions available. Then again, calling Reasonator a hack is a disservice to the real application it provides.

When I associate "is a list of" with categories in Wikidata, I express reasonable expectations about what such a category should be about. Presidents of the USA for instance are human and they hold or held the office of President of the USA. This excludes Lex Luthor who is shown as one in Reasonator because it does not make the human restriction.

With the results of the queries several things are expressed. Obviously the results of the query but implicitly it shows "local" articles that are not categorised. It shows items that may or may not have an article elsewhere. Yes, I use it when I add statements to items. It does show up in Reasonator, in WDQ results, in automated descriptions and as interestingly it will end up in the tool by Markus.

The application of the "is a list of" in categories is powerful. It gives clues about a subset of data. When people have an application for it, they concentrate on it. For instance there was a project on "members of the Lok Sabha" and another on "members of the European parliament". The results of the work done prevented a lot of duplicate items.. (who would expect for the Romanian Wikipedia to be among the best in knowing about members of the European parliament?)

When I talk about query, I talk about WDQ and its results. There is no alternative at this time. Consider for instance the tool of Markus. It may have already have a limited application for some but as long as it does not update itself, it is not as illustrative as the WDQ by Magnus and it cannot be used in the same way to improve Wikidata as is possible by many of the tools by Magnus.

The official query happens when it does. When it does it will severely stunted. This is because the "simple" queries will not have the power to make them as illustrative as the queries used by the "is a list of". Obviously I cannot wait until this situation is reversed. Having to convert the existing queries is a pain but it is a nice pain.

As I explained at Wikimania, it is all in the application. When there is one, it makes sense to have it. Without an application it is at best a nice effort we can talk about. But hey, I have a limited amount of time so I prefer to concentrate on application of functionality and data.

Thanks,

GerardM

On 20 August 2014 09:36, Markus Krötzsch <markus@semantic-mediawiki.org> wrote:

On 19.08.2014 22:23, David Cuenca wrote:
...

Actually I have one last question :) At the moment Gerard is using "is
a list of:<value>" on category item pages which has the effect of being
the inverse of "instance of". And then he adds further conditions as
qualifiers, see:
https://www.wikidata.org/wiki/Q6562

While this method of works for simple categories, more complex ones
would be hard to model using this method, like
https://www.wikidata.org/wiki/Q8380098

I was thinking of modelling it like:
<Category:Discoverers of extrasolar planets> is a list of <human>
<Category:Discoverers of extrasolar planets> has items used as value of
<discoverer>

Of course it would require to have a link between the item "discoverer"
and the property "discoverer", but would that make sense?

Well, it depends on what the intended use of "is a list of" is. First note that it is not the inverse of "instance of" (the inverse of a relation R holds between all pairs where R holds, just in the opposite direction; this is not what happens here). Rather, "is a list of" describes some class that all of the elements of a list are instances of.

I don't think that it one should try to capture *exactly* what the items on the list are. Many lists are based on complicated criteria and it would be very hard to express them in a good way using statements. What you suggest above would be an ad hoc solution (a.k.a. hack) for a few cases; many other cases would need different features. Even if one would have a way to capture some lists exactly, one would need to document this very carefully in order for the information to be useful to others. In essence, one would specify a query language there. Since we already are working on queries for Wikidata, the better way to solve this in the future would be to refer to actual queries (as soon as they are expressive enough).

Anyway, as I understand it, Gerard is adding these statements to help with the organisation of lists (and to give some more relevant statements to list items, e.g., to assist the auto description). Since we want to support automated list generation in the future (using query results on Wikipedia pages), it might be handy to have some overview of the lists (how many, about which topics, etc.). But I am just guessing here -- maybe Gerard has other reasons too.

Cheers,

Markus

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