RDF terms in rdflib¶
Terms are the kinds of objects that can appear in a quoted/asserted triples. Those that are part of core RDF concepts are: Blank Node
, URI Reference
and Literal
, the latter consisting of a literal value and either a datatype or an RFC 3066 language tag.
All terms in RDFLib are sub-classes of the rdflib.term.Identifier
class.
Nodes are a subset of the Terms that the underlying store actually persists. The set of such Terms depends on whether or not the store is formula-aware. Stores that aren’t formula-aware would only persist those terms core to the RDF Model, and those that are formula-aware would be able to persist the N3 extensions as well. However, utility terms that only serve the purpose for matching nodes by term-patterns probably will only be terms and not nodes.
BNodes¶
In RDF, a blank node (also called BNode) is a node in an RDF graph representing a resource for which a URI or literal is not given. The resource represented by a blank node is also called an anonymous resource. By RDF standard a blank node can only be used as subject or object in an RDF triple, although in some syntaxes like Notation 3 [1] it is acceptable to use a blank node as a predicate. If a blank node has a node ID (not all blank nodes are labelled in all RDF serializations), it is limited in scope to a serialization of a particular RDF graph, i.e. the node p1 in the subsequent example does not represent the same node as a node named p1 in any other graph –wikipedia
>>> from rdflib import BNode
>>> anode = BNode()
>>> anode
rdflib.term.BNode('AFwALAKU0')
>>> anode.n3()
u'_:AFwALAKU0'
URIRefs¶
A URI reference within an RDF graph is a Unicode string that does not contain any control characters ( #x00 - #x1F, #x7F-#x9F) and would produce a valid URI character sequence representing an absolute URI with optional fragment identifier – W3 RDF Concepts
>>> from rdflib import URIRef
>>> aref = URIRef()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: __new__() takes at least 2 arguments (1 given)
>>> aref = URIRef('')
>>> aref
rdflib.term.URIRef(u'')
>>> aref = URIRef('http://example.com')
>>> aref
rdflib.term.URIRef(u'http://example.com')
>>> aref.n3()
u'<http://example.com>'
Literals¶
Literals are the attribute values in RDF, for instance, a person’s name, the date of birth, height, etc. Literals can have a data-type (i.e. this is a double) or a language tag (this label is in English).
Note
When using the language tag, care must be taken not to confuse language with locale. The language tag relates only to human language text. Presentational issues should be addressed in end-user applications.
Note
The case normalization of language tags is part of the description of the abstract syntax, and consequently the abstract behaviour of RDF applications. It does not constrain an RDF implementation to actually normalize the case. Crucially, the result of comparing two language tags should not be sensitive to the case of the original input. – RDF Concepts and Abstract Syntax
Python support¶
RDFLib Literals essentially behave like unicode characters with an XML Schema datatype or language attribute.

The class provides a mechanism to both convert Python literals (and their built-ins such as time/date/datetime) into equivalent RDF Literals and (conversely) convert Literals to their Python equivalent. This mapping to and from Python literals is done as follows:
XML Datatype | Python type |
---|---|
None | None [1] |
xsd:time | time [2] |
xsd:date | date |
xsd:dateTime | datetime |
xsd:string | None |
xsd:normalizedString | None |
xsd:token | None |
xsd:language | None |
xsd:boolean | boolean |
xsd:decimal | Decimal |
xsd:integer | long |
xsd:nonPositiveInteger | int |
xsd:long | long |
xsd:nonNegativeInteger | int |
xsd:negativeInteger | int |
xsd:int | long |
xsd:unsignedLong | long |
xsd:positiveInteger | int |
xsd:short | int |
xsd:unsignedInt | long |
xsd:byte | int |
xsd:unsignedShort | int |
xsd:unsignedByte | int |
xsd:float | float |
xsd:double | float |
xsd:base64Binary | base64 |
xsd:anyURI | None |
rdf:XMLLiteral | xml.dom.minidom.Document [3] |
rdf:HTML | xml.dom.minidom.DocumentFragment |
[1] | plain literals map directly to value space |
[2] | Date, time and datetime literals are mapped to Python instances using the isodate package). |
[3] | this is a bit dirty - by accident the html5lib parser
produces DocumentFragments , and the xml parser Documents ,
letting us use this to decide what datatype when round-tripping. |
An appropriate data-type and lexical representation can be found using:
and the other direction with
All this happens automatically when creating Literal
objects by passing Python objects to the constructor, and you never have to do this manually.
You can add custom data-types with rdflib.term.bind()
, see also examples.custom_datatype