Example of finding relationships between band genres using SPARQL queries over DBPedia Linked Data

linked data bands.ipynb

linkeddataquery.py

# 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)