Vazaar Project Blog

After some headaches I’ve found how to write dynamic SPARQL queries by passing parameters. For example, to query graph about resources collected last hour this code could be a first approach:

#!/usr/bin/env python
# Dynamic query (example code)

from datetime import datetime
import rdflib
from namespaces import XSD

def last_day():
    """ get date """
    now = datetime.now()
    date = now - timedelta(hours=24)

    return date

def get_date_filtered_query():
    """ build query """
    period = last_day()
    mydate = Literal(period, datatype=URIRef(XSD))

    query = """
        PREFIX rdf: 
        PREFIX nie: 
        PREFIX nfo: 
        PREFIX nao: 
        PREFIX pimo: 
        PREFIX xsd: 
        SELECT ?id
        WHERE
        {
            ?id rdf:type ?type .
            ?id nao:created ?date .
            FILTER (?type != pimo:Collection) .
            FILTER (xsd:dateTime(?date) >= xsd:dateTime("%s")) .
        }
        ORDER BY DESC(?date)
        """ % mydate

    return query

# query graph
query = get_date_filtered_query()
result = graph.query(query)

for id in result.selected:
    print id

For more information is worth to take a look W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes. A self explained list of XML datatypes: