Subject: Re: [Wikidata] Linked data fragment enabled on the
Query Service



Hi!

> In the queries I tried, no results were streaming in whatsoever. I have

I've tried the "antarctic rivers" query:

SELECT ?river ?riverLabel ?location
WHERE
{
?river wdt:P31/wdt:P279* wd:Q355304;
wdt:P30 wd:Q51.
OPTIONAL { ?river wdt:P625 ?location. }
}

and after waiting for a very long time I got like 2 results. But that
took very long. Also, I suspect this engine does not implement path
queries right, e.g. I get queries like this:

https://query.wikidata.org/bigdata/ldf?subject=http%3A%2F%2Fwww.wikidata.org%2Fentity%2FQ7994940&object=http%3A%2F%2Fwww.wikidata.org%2Fentity%2FQ355304

i.e. it tries to match Q7994940-*-Q355304. But instead of that, it
should be trying Q7994940-P31-* and seeing whether Q355304 is there, and
if not, keeping those for matching via P279.

Also, if I rewrite query like this:

SELECT ?river ?riverLabel ?location
WHERE
{
?river wdt:P30 wd:Q51; wdt:P31/wdt:P279* wd:Q355304 .
OPTIONAL { ?river wdt:P625 ?location. }
}

It takes it about 1000(!) s to find the first river, and it only found
two that are directly P31, so I suspect path queries are not going to
work that well. I wonder whether it does breadth-first search somehow?

--
Stas Malyshev
smalyshev@xxxxxxxxxxxxx

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