Jheald added a subscriber: Jheald.
Jheald added a comment.
Transitive properties aren't necessary a-cyclic -- for example, consider
https://phabricator.wikimedia.org/P460 "said to be the same as", which is
transitive, currently used to link given names together, if they are considered
to be variants of the same name in different languages.
The page at
https://www.wikidata.org/wiki/Wikidata:WikiProject_Names/given-name_variants
includes two columns of queries that find all the variants of each name (ie
extract the whole equivalence class), using a
https://phabricator.wikimedia.org/P460* path query from a given starting name,
and count up the number of occurrences of each one.
https://phabricator.wikimedia.org/P460 is transitive, but it is not directed,
and so there are huge numbers of loops in the equivalence classes. But this
isn't a problem. The path search just keeps going until no new
https://phabricator.wikimedia.org/P460 link leads it to a node it has not
already seen. So the engine //can// handles path loops, without a problem.
Similarly, looking at the query Daniel posted,
SELECT (COUNT(DISTINCT(?city)) AS ?count) WHERE {
?city wdt:P31/wdt:P279* wd:Q515 .# find instances of subclasses of city
?city wdt:P131* wd:Q1202 .
}
if one comments out either one or the other of the two requirement lines, the
query runs without a hitch. So I don't think there is anything to do with the
nature of the data (eg whether it contains cycles or not) that affects whether
or not Blazegraph can handle it.
The problem appears to arise with how Blazegraph combines the two requirements.
Related to this may be the fact that Blazegraph also fails with path searches
of the form
SELECT (COUNT(DISTINCT ?a) AS ?count) WHERE {
BIND (wd:Q3305213 AS ?class) .# paintings
?a wdt:P31/wdt:P279* ?class .
}
even though the same search works perfectly if the variable ?class is
eliminated, and wd:Q3305213 instead specified inline.
I filed the latter with Blazegraph as issue 1543 three weeks ago, but no
commentary on it from them as yet
https://jira.blazegraph.com/browse/BLZG-1543
TASK DETAIL
https://phabricator.wikimedia.org/T116298
EMAIL PREFERENCES
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To: Smalyshev, Jheald
Cc: Jheald, Aklapper, daniel, jkroll, Smalyshev, Wikidata-bugs, Jdouglas, aude,
Deskana, Manybubbles
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