Selecting literal values from Wikidata federated query service using RDFLib

Question

I'm trying to get external identifiers for an entity in Wikidata. Using the following query, I can get the literal values (_value) and optionally formatted URLs (value) for Q2409 on the Wikidata Query Service site.

Load in Wikidata Query Service

SELECT ?property ?_value ?value
WHERE {
  ?property wikibase:propertyType wikibase:ExternalId .
  ?property wikibase:directClaim ?propertyclaim .
  OPTIONAL { ?property wdt:P1630 ?formatterURL . }
  wd:Q2409 ?propertyclaim ?_value .
  BIND(IF(BOUND(?formatterURL), IRI(REPLACE(?formatterURL, "\\$", ?_value)) , ?_value) AS ?value)
}

Using RDFLib, I'm writing the same query, but with a federated service.

from rdflib import Graph
from rdflib.plugins.sparql import prepareQuery

g = Graph()
q = prepareQuery(r"""
  PREFIX wd: <http://www.wikidata.org/entity/>
  PREFIX wdt: <http://www.wikidata.org/prop/direct/>
  PREFIX wikibase: <http://wikiba.se/ontology#>

  SELECT ?property ?_value ?value
  WHERE {
    SERVICE <https://query.wikidata.org/sparql> {
      ?property wikibase:propertyType wikibase:ExternalId .
      ?property wikibase:directClaim ?propertyclaim .
      OPTIONAL { ?property wdt:P1630 ?formatterURL . }
      wd:Q2409 ?propertyclaim ?_value .
      BIND(IF(BOUND(?formatterURL), IRI(REPLACE(?formatterURL, "\\$", ?_value)) , ?_value) AS ?value)
    }
  }
""")

for row in g.query(q, DEBUG=True):
  print(row)

With this, I'm getting the URLs as URIRef objects. But, instead of Literal for the literal values, I'm getting None.

First 6 lines of output:

(rdflib.term.URIRef('http://www.wikidata.org/entity/P232'), None, None)
(rdflib.term.URIRef('http://www.wikidata.org/entity/P657'), None, None)
(rdflib.term.URIRef('http://www.wikidata.org/entity/P6366'), None, None)
(rdflib.term.URIRef('http://www.wikidata.org/entity/P1296'), None, rdflib.term.URIRef('https://www.enciclopedia.cat/EC-GEC-01407541.xml'))
(rdflib.term.URIRef('http://www.wikidata.org/entity/P486'), None, rdflib.term.URIRef('https://id.nlm.nih.gov/mesh/D0068511.html'))
(rdflib.term.URIRef('http://www.wikidata.org/entity/P7033'), None, rdflib.term.URIRef('http://vocabulary.curriculum.edu.au/scot/5001.html'))

What am I missing for the literal values? I'm having trouble figuring out why I'm getting None instead of the values.

score 0 · Answer 1 · answered Feb 17 '22 at 06:47

I'm not sure if all of the features of SERVICE calls are fully implemented in RDFLib.

I would get this working with a 'normal' call the Wikidata SPARQL endpoint using either RDFLib's SPARQLWrapper library or the general-purpose web request Python libraries requests or httpx first. If that all works, you could then try again with the SERVICE request but you likely won't need it.

Selecting literal values from Wikidata federated query service using RDFLib

1 Answers1