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Example of finding relationships between band genres using SPARQL queries over DBPedia Linked Data
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# Import the necessary packages
from SPARQLWrapper import SPARQLWrapper, JSON
# Add some helper functions
# A function that will return the results of running a SPARQL query with
# a defined set of prefixes over a specified endpoint.
# It follows the same five-step process apart from creating the query, which
# is provided as an argument to the function.
def runQuery(endpoint, prefix, q):
''' Run a SPARQL query with a declared prefix over a specified endpoint '''
sparql = SPARQLWrapper(endpoint)
sparql.setQuery(prefix+q) # concatenate the strings representing the prefixes and the query
sparql.setReturnFormat(JSON)
return sparql.query().convert()
# Import pandas to provide facilities for creating a DataFrame to hold results
import pandas as pd
# Function to convert query results into a DataFrame
# The results are assumed to be in JSON format and therefore the Python dictionary will have
# the results indexed by 'results' and then 'bindings'.
def dict2df(results):
''' A function to flatten the SPARQL query results and return the column values '''
data = []
for result in results["results"]["bindings"]:
tmp = {}
for el in result:
tmp[el] = result[el]['value']
data.append(tmp)
df = pd.DataFrame(data)
return df
# Function to run a query and return results in a DataFrame
def dfResults(endpoint, prefix, q):
''' Generate a data frame containing the results of running
a SPARQL query with a declared prefix over a specified endpoint '''
return dict2df(runQuery(endpoint, prefix, q))
# Print a limited number of results of a query
def printQuery(results, limit=''):
''' Print the results from the SPARQL query '''
resdata = results["results"]["bindings"]
if limit != '':
resdata = results["results"]["bindings"][:limit]
for result in resdata:
for ans in result:
print('{0}: {1}'.format(ans, result[ans]['value']))
print()
# Run a query and print out a limited number of results
def printRunQuery(endpoint, prefix, q, limit=''):
''' Print the results from the SPARQL query '''
results = runQuery(endpoint, prefix, q)
printQuery(results, limit)
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