Resource

The Resource class wraps a Graph and a resource reference (i.e. a rdflib.term.URIRef or rdflib.term.BNode) to support a resource-oriented way of working with a graph.

It contains methods directly corresponding to those methods of the Graph interface that relate to reading and writing data. The difference is that a Resource also binds a resource identifier, making it possible to work without tracking both the graph and a current subject. This makes for a “resource oriented” style, as compared to the triple orientation of the Graph API.

Resulting generators are also wrapped so that any resource reference values (rdflib.term.URIRef`s and :class:`rdflib.term.BNode`s) are in turn wrapped as Resources. (Note that this behaviour differs from the corresponding methods in :class:`~rdflib.graph.Graph, where no such conversion takes place.)

Basic Usage Scenario

Start by importing things we need and define some namespaces:

>>> from rdflib import *
>>> FOAF = Namespace("http://xmlns.com/foaf/0.1/")
>>> CV = Namespace("http://purl.org/captsolo/resume-rdf/0.2/cv#")

Load some RDF data:

>>> graph = Graph().parse(format='n3', data='''
... @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
... @prefix xsd: <http://www.w3.org/2001/XMLSchema#>.
... @prefix foaf: <http://xmlns.com/foaf/0.1/> .
... @prefix cv: <http://purl.org/captsolo/resume-rdf/0.2/cv#> .
...
... @base <http://example.org/> .
...
... </person/some1#self> a foaf:Person;
...     rdfs:comment "Just a Python & RDF hacker."@en;
...     foaf:depiction </images/person/some1.jpg>;
...     foaf:homepage <http://example.net/>;
...     foaf:name "Some Body" .
...
... </images/person/some1.jpg> a foaf:Image;
...     rdfs:label "some 1"@en;
...     rdfs:comment "Just an image"@en;
...     foaf:thumbnail </images/person/some1-thumb.jpg> .
...
... </images/person/some1-thumb.jpg> a foaf:Image .
...
... [] a cv:CV;
...     cv:aboutPerson </person/some1#self>;
...     cv:hasWorkHistory [ cv:employedIn </#company>;
...             cv:startDate "2009-09-04"^^xsd:date ] .
... ''')

Create a Resource:

>>> person = Resource(
...     graph, URIRef("http://example.org/person/some1#self"))

Retrieve some basic facts:

>>> person.identifier
rdflib.term.URIRef(u'http://example.org/person/some1#self')

>>> person.value(FOAF.name)
rdflib.term.Literal(u'Some Body')

>>> person.value(RDFS.comment)
rdflib.term.Literal(u'Just a Python & RDF hacker.', lang=u'en')

Resources as unicode are represented by their identifiers as unicode:

>>> unicode(person)  
u'Resource(http://example.org/person/some1#self'

Resource references are also Resources, so you can easily get e.g. a qname for the type of a resource, like:

>>> person.value(RDF.type).qname()
u'foaf:Person'

Or for the predicates of a resource:

>>> sorted(
...     p.qname() for p in person.predicates()
... )  
[u'foaf:depiction', u'foaf:homepage',
 u'foaf:name', u'rdf:type', u'rdfs:comment']

Follow relations and get more data from their Resources as well:

>>> for pic in person.objects(FOAF.depiction):
...     print(pic.identifier)
...     print(pic.value(RDF.type).qname())
...     print(pic.label())
...     print(pic.comment())
...     print(pic.value(FOAF.thumbnail).identifier)
http://example.org/images/person/some1.jpg
foaf:Image
some 1
Just an image
http://example.org/images/person/some1-thumb.jpg

>>> for cv in person.subjects(CV.aboutPerson):
...     work = list(cv.objects(CV.hasWorkHistory))[0]
...     print(work.value(CV.employedIn).identifier)
...     print(work.value(CV.startDate))
http://example.org/#company
2009-09-04

It’s just as easy to work with the predicates of a resource:

>>> for s, p in person.subject_predicates():
...     print(s.value(RDF.type).qname())
...     print(p.qname())
...     for s, o in p.subject_objects():
...         print(s.value(RDF.type).qname())
...         print(o.value(RDF.type).qname())
cv:CV
cv:aboutPerson
cv:CV
foaf:Person

This is useful for e.g. inspection:

>>> thumb_ref = URIRef("http://example.org/images/person/some1-thumb.jpg")
>>> thumb = Resource(graph, thumb_ref)
>>> for p, o in thumb.predicate_objects():
...     print(p.qname())
...     print(o.qname())
rdf:type
foaf:Image

Similarly, adding, setting and removing data is easy:

>>> thumb.add(RDFS.label, Literal("thumb"))
>>> print(thumb.label())
thumb
>>> thumb.set(RDFS.label, Literal("thumbnail"))
>>> print(thumb.label())
thumbnail
>>> thumb.remove(RDFS.label)
>>> list(thumb.objects(RDFS.label))
[]

Schema Example

With this artificial schema data:

>>> graph = Graph().parse(format='n3', data='''
... @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
... @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
... @prefix owl: <http://www.w3.org/2002/07/owl#> .
... @prefix v: <http://example.org/def/v#> .
...
... v:Artifact a owl:Class .
...
... v:Document a owl:Class;
...     rdfs:subClassOf v:Artifact .
...
... v:Paper a owl:Class;
...     rdfs:subClassOf v:Document .
...
... v:Choice owl:oneOf (v:One v:Other) .
...
... v:Stuff a rdf:Seq; rdf:_1 v:One; rdf:_2 v:Other .
...
... ''')

From this class:

>>> artifact = Resource(graph, URIRef("http://example.org/def/v#Artifact"))

we can get at subclasses:

>>> subclasses = list(artifact.transitive_subjects(RDFS.subClassOf))
>>> [c.qname() for c in subclasses]
[u'v:Artifact', u'v:Document', u'v:Paper']

and superclasses from the last subclass:

>>> [c.qname() for c in subclasses[-1].transitive_objects(RDFS.subClassOf)]
[u'v:Paper', u'v:Document', u'v:Artifact']

Get items from the Choice:

>>> choice = Resource(graph, URIRef("http://example.org/def/v#Choice"))
>>> [it.qname() for it in choice.value(OWL.oneOf).items()]
[u'v:One', u'v:Other']

And the sequence of Stuff:

>>> stuff = Resource(graph, URIRef("http://example.org/def/v#Stuff"))
>>> [it.qname() for it in stuff.seq()]
[u'v:One', u'v:Other']
On add, other resources are auto-unboxed:
>>> paper = Resource(graph, URIRef("http://example.org/def/v#Paper"))
>>> paper.add(RDFS.subClassOf, artifact)
>>> artifact in paper.objects(RDFS.subClassOf) # checks Resource instance
True
>>> (paper._identifier, RDFS.subClassOf, artifact._identifier) in graph
True

Technical Details

Comparison is based on graph and identifier:

>>> g1 = Graph()
>>> t1 = Resource(g1, URIRef("http://example.org/thing"))
>>> t2 = Resource(g1, URIRef("http://example.org/thing"))
>>> t3 = Resource(g1, URIRef("http://example.org/other"))
>>> t4 = Resource(Graph(), URIRef("http://example.org/other"))

>>> t1 is t2
False

>>> t1 == t2
True
>>> t1 != t2
False

>>> t1 == t3
False
>>> t1 != t3
True

>>> t3 != t4
True

>>> t3 < t1 and t1 > t3
True
>>> t1 >= t1 and t1 >= t3
True
>>> t1 <= t1 and t3 <= t1
True

>>> t1 < t1 or t1 < t3 or t3 > t1 or t3 > t3
False

Hash is computed from graph and identifier:

>>> g1 = Graph()
>>> t1 = Resource(g1, URIRef("http://example.org/thing"))

>>> hash(t1) == hash(Resource(g1, URIRef("http://example.org/thing")))
True

>>> hash(t1) == hash(Resource(Graph(), t1.identifier))
False
>>> hash(t1) == hash(Resource(Graph(), URIRef("http://example.org/thing")))
False

The Resource class is suitable as a base class for mapper toolkits. For example, consider this utility for accessing RDF properties via qname-like attributes:

>>> class Item(Resource):
...
...     def __getattr__(self, p):
...         return list(self.objects(self._to_ref(*p.split('_', 1))))
...
...     def _to_ref(self, pfx, name):
...         return URIRef(self._graph.store.namespace(pfx) + name)

It works as follows:

>>> graph = Graph().parse(format='n3', data='''
... @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
... @prefix foaf: <http://xmlns.com/foaf/0.1/> .
...
... @base <http://example.org/> .
... </person/some1#self>
...     foaf:name "Some Body";
...     foaf:depiction </images/person/some1.jpg> .
... </images/person/some1.jpg> rdfs:comment "Just an image"@en .
... ''')

>>> person = Item(graph, URIRef("http://example.org/person/some1#self"))

>>> print(person.foaf_name[0])
Some Body

The mechanism for wrapping references as resources cooperates with subclasses. Therefore, accessing referenced resources automatically creates new Item objects:

>>> isinstance(person.foaf_depiction[0], Item)
True

>>> print(person.foaf_depiction[0].rdfs_comment[0])
Just an image

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