Page MenuHomePhabricator

Linked Data Fragments endpoint returns IllegalStateException
Closed, ResolvedPublic5 Estimated Story Points

Description

As received on wikidata ML:

I am trying to get alternative names of given names in WikiData with the
following simple query:

PREFIX ps: <http://www.wikidata.org/prop/direct/>
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
CONSTRUCT {?s rdfs:label ?o}
WHERE { ?s ps:P31 wd:Q202444. ?s rdfs:label ?o}
LIMIT 1000

Initially, the query was much more complex, but I was getting time-outs on
the public WikiData SPARQL endpoint. I decided to use Linked Data Fragments
to offload some filtering from the server to the client.

comunica-sparql "https://query.wikidata.org/bigdata/ldf" -f query > given_names.n3

(where "query" is a file with the SPARQL query shown above). Unfortunately,
the client tries to get output from the 3rd page, I am getting
the following error:

Could not retrieve https://query.wikidata.org/bigdata/ldf?subject=http%3A%2F%2Fwww.wikidata.org%2Fentity%2FQ21147790&predicate=http%3A%2F%2Fwww.w3.org%2F2000%2F01%2Frdf-schema%23label&page=3 (500: unknown error)

Following the link in fact returns HTTP 500 error with

Error details
java.lang.IllegalStateException

The link points to the 3rd page. It works if you try to go the second page:
https://query.wikidata.org/bigdata/ldf?subject=http%3A%2F%2Fwww.wikidata.org%2Fentity%2FQ21147790&predicate=http%3A%2F%2Fwww.w3.org%2F2000%2F01%2Frdf-schema%23label&page=2

Is this a bug or a limitation of a service?

Event Timeline

Restricted Application added a subscriber: Aklapper. · View Herald Transcript

I responded to Maciej (the one who reported the problem originally) on the mailing list. Looks like we accidentally gave them the wrong ticket number earlier: https://lists.wikimedia.org/pipermail/wikidata/2021-January/014451.html

Looks like this ticket hasn't been triaged/assigned yet

CBogen set the point value for this task to 5.Jan 25 2021, 4:47 PM

Change 676366 had a related patch set uploaded (by DCausse; author: DCausse):

[wikidata/query/rdf@master] Fix pagination in LDF mode

https://gerrit.wikimedia.org/r/676366

Change 676366 merged by jenkins-bot:

[wikidata/query/rdf@master] Fix pagination in LDF mode

https://gerrit.wikimedia.org/r/676366