Queries

SuRF aims to integrate RDF with the object-oriented paradigm so that manual writing and execution of SPARQL queries is seldom needed. Resources and classes provide a higher level of abstraction than queries do and they should cover the most common use cases.

Executing arbitrary SPARQL queries

It is still possible to execute arbitrary queries in the cases where this is needed. The surf.store.Store class provides the method: surf.store.Store.execute_sparql() which accepts the query as a string. This method will return raw results, and SuRF will make no attempt to represent returned data as resource objects.

>>> import surf
>>> from surf.rdf import URIRef
>>> sess = surf.Session(surf.Store(reader="rdflib", writer="rdflib"))
>>> sess.default_store.add_triple(URIRef("http://s"), URIRef("http://p"), "value!")

>>> sess.default_store.execute_sparql("SELECT ?s ?p ?o WHERE { ?s ?p ?o }")
<rdflib.sparql.QueryResult.SPARQLQueryResult object at ...>

>>> list(sess.default_store.execute_sparql("SELECT ?s ?p ?o WHERE { ?s ?p ?o }"))
[(rdflib.URIRef('http://s'), rdflib.URIRef('http://p'), 'value!')]

Constructing queries in a programmatic way

SuRF also provides utilities for programmatic construction of dynamic SPARQL queries in the surf.query module. Using them can sometimes result in cleaner code than constructing queries by string concatenation. Here’s an example on how to use the tools available in the surf.query module:

>>> import surf
>>> from surf.query import a, select
>>> query = select("?s", "?src")
>>> query.named_group("?src", ("?s", a, surf.ns.FOAF['Person']))
>>> print unicode(query)
SELECT  ?s ?src  WHERE {  GRAPH ?src {  ?s <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person>  }  }