Federated queries with Virtuoso

Federated queries with Virtuoso.py

"""Federated queries with Virtuoso."""


import sys

from SPARQLWrapper import SPARQLWrapper, JSON


QUERY_WIKIDATA = """
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>

SELECT ?work WHERE {
  SERVICE <https://query.wikidata.org/sparql> {
    SELECT ?work WHERE {
      ?work wdt:P50 wd:Q159552 .
    }
  }
}
"""

QUERY_DBPEDIA = """
PREFIX dbo: <http://dbpedia.org/ontology/> 
PREFIX dbr: <http://dbpedia.org/resource/> 

SELECT ?work
WHERE {
 SERVICE <http://DBpedia.org/sparql> {
   SELECT ?work WHERE {
     ?work dbo:author dbr:Johannes_V._Jensen .
   }
 }
}
"""

QUERY_BOTH = """
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>
PREFIX dbo: <http://dbpedia.org/ontology/> 
PREFIX dbr: <http://dbpedia.org/resource/> 

SELECT ?work WHERE {
  {
    SERVICE <https://query.wikidata.org/sparql> {
      SELECT ?work WHERE {
        ?work wdt:P50 wd:Q159552 .
      }
    }
  }
  UNION 
  {
    SERVICE <http://DBpedia.org/sparql> {
      SELECT ?work WHERE {
        ?work dbo:author dbr:Johannes_V._Jensen .
      }
    }
  }
}
"""

query = QUERY_BOTH
if len(sys.argv) == 2:
    if sys.argv[1] == 'wikidata':
        query = QUERY_WIKIDATA
    elif sys.argv[1] == 'dbpedia':
        query = QUERY_DBPEDIA
    else:
        raise ValueError('input argument wrong')


sparql = SPARQLWrapper("http://127.0.0.1:8890/sparql")
sparql.setQuery(query)
sparql.setReturnFormat(JSON)
results = sparql.query().convert()

for result in results["results"]["bindings"]:
    print(result) 

There is a server error in your QUERY_BOTH. If you change the dbpedia service to tolower dbpedia in line 52 it works in 2022