Module rdflib.Graph
Instanciating Graphs with default store (IOMemory) and default
identifier (a BNode):
>>> g=Graph()
>>> g.store.__class__
<class 'rdflib.store.IOMemory.IOMemory'>
>>> g.identifier.__class__
<class 'rdflib.BNode.BNode'>
Instanciating Graphs with a specific kind of store (IOMemory) and a
default identifier (a BNode):
Other store kinds: Sleepycat, MySQL, ZODB, SQLite
>>> store = plugin.get('IOMemory',Store)()
>>> store.__class__.__name__
'IOMemory'
>>> graph = Graph(store)
>>> graph.store.__class__
<class 'rdflib.store.IOMemory.IOMemory'>
Instanciating Graphs with Sleepycat store and an identifier -
<http://rdflib.net>:
>>> g=Graph('Sleepycat',URIRef("http://rdflib.net"))
>>> g.identifier
u'http://rdflib.net'
>>> str(g)
"<http://rdflib.net> a rdfg:Graph;rdflib:storage [a rdflib:Store;rdfs:label 'Sleepycat']."
Creating a ConjunctiveGraph - The top level container for all named
Graphs in a 'database':
>>> g=ConjunctiveGraph()
>>> str(g.default_context)
"[a rdfg:Graph;rdflib:storage [a rdflib:Store;rdfs:label 'IOMemory']]."
Adding / removing reified triples to Graph and iterating over it
directly or via triple pattern:
>>> g=Graph('IOMemory')
>>> statementId = BNode()
>>> print len(g)
0
>>> g.add((statementId,RDF.type,RDF.Statement))
>>> g.add((statementId,RDF.subject,URIRef('http://rdflib.net/store/ConjunctiveGraph')))
>>> g.add((statementId,RDF.predicate,RDFS.label))
>>> g.add((statementId,RDF.object,Literal("Conjunctive Graph")))
>>> print len(g)
4
>>> for s,p,o in g: print type(s)
...
<class 'rdflib.BNode.BNode'>
<class 'rdflib.BNode.BNode'>
<class 'rdflib.BNode.BNode'>
<class 'rdflib.BNode.BNode'>
>>> for s,p,o in g.triples((None,RDF.object,None)): print o
...
Conjunctive Graph
>>> g.remove((statementId,RDF.type,RDF.Statement))
>>> print len(g)
3
None terms in calls to triple can be thought of as 'open
variables'
Graph Aggregation - ConjunctiveGraphs and ReadOnlyGraphAggregate
within the same store:
>>> store = plugin.get('IOMemory',Store)()
>>> g1 = Graph(store)
>>> g2 = Graph(store)
>>> g3 = Graph(store)
>>> stmt1 = BNode()
>>> stmt2 = BNode()
>>> stmt3 = BNode()
>>> g1.add((stmt1,RDF.type,RDF.Statement))
>>> g1.add((stmt1,RDF.subject,URIRef('http://rdflib.net/store/ConjunctiveGraph')))
>>> g1.add((stmt1,RDF.predicate,RDFS.label))
>>> g1.add((stmt1,RDF.object,Literal("Conjunctive Graph")))
>>> g2.add((stmt2,RDF.type,RDF.Statement))
>>> g2.add((stmt2,RDF.subject,URIRef('http://rdflib.net/store/ConjunctiveGraph')))
>>> g2.add((stmt2,RDF.predicate,RDF.type))
>>> g2.add((stmt2,RDF.object,RDFS.Class))
>>> g3.add((stmt3,RDF.type,RDF.Statement))
>>> g3.add((stmt3,RDF.subject,URIRef('http://rdflib.net/store/ConjunctiveGraph')))
>>> g3.add((stmt3,RDF.predicate,RDFS.comment))
>>> g3.add((stmt3,RDF.object,Literal("The top-level aggregate graph - The sum of all named graphs within a Store")))
>>> len(list(ConjunctiveGraph(store).subjects(RDF.type,RDF.Statement)))
3
>>> len(list(ReadOnlyGraphAggregate([g1,g2]).subjects(RDF.type,RDF.Statement)))
2
ConjunctiveGraphs have a 'quads' method which returns quads instead of
triples, where the fourth item is the Graph (or subclass thereof)
instance in which the triple was asserted:
>>> from sets import Set
>>> uniqueGraphNames = Set([graph.identifier for s,p,o,graph in ConjunctiveGraph(store).quads((None,RDF.predicate,None))])
>>> len(uniqueGraphNames)
3
>>> unionGraph = ReadOnlyGraphAggregate([g1,g2])
>>> uniqueGraphNames = Set([graph.identifier for s,p,o,graph in unionGraph.quads((None,RDF.predicate,None))])
>>> len(uniqueGraphNames)
2
Parsing N3 from StringIO
>>> g2=Graph()
>>> src = """
... @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
... @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
... [ a rdf:Statement ;
... rdf:subject <http://rdflib.net/store/ConjunctiveGraph>;
... rdf:predicate rdfs:label;
... rdf:object "Conjunctive Graph" ] """
>>> g2=g2.parse(StringIO(src),format='n3')
>>> print len(g2)
4
Using Namespace class:
>>> RDFLib = Namespace('http://rdflib.net')
>>> RDFLib.ConjunctiveGraph
u'http://rdflib.netConjunctiveGraph'
>>> RDFLib['Graph']
u'http://rdflib.netGraph'
SPARQL Queries
>>> print len(g)
3
>>> q = '''
... PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?pred WHERE { ?stmt rdf:predicate ?pred. }
... '''
>>> for pred in g.query(q): print pred
(u'http://www.w3.org/2000/01/rdf-schema#label',)
SPARQL Queries with namespace bindings as argument
>>> nsMap = {u"rdf":RDF.RDFNS}
>>> for pred in g.query("SELECT ?pred WHERE { ?stmt rdf:predicate ?pred. }", initNs=nsMap): print pred
(u'http://www.w3.org/2000/01/rdf-schema#label',)
Parameterized SPARQL Queries
>>> top = { Variable("?term") : RDF.predicate }
>>> for pred in g.query("SELECT ?pred WHERE { ?stmt ?term ?pred. }", initBindings=top): print pred
(u'http://www.w3.org/2000/01/rdf-schema#label',)