Blank node
Encyclopedia
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
it is acceptable to use a blank node as a predicate. If a blank node has a node ID (not all blank nodes are labeled 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.
ex:John foaf:knows _:p1
_:p1 foaf:birthDate 04-21
The first triple reads "John knows p1". The second triple reads "p1 is born on April 21st"
ex:John is a named resource, which means this resource is absolutely identified by the URI obtained by replacing the ex: prefix by the XML namespace it stands for, such ashttp://example.org/Person#John .
_:p1 represents John's anonymous friend, not identified by a URI. One can know by the semantics declared in the FOAF
vocabulary that the class of _:p1 is foaf:Person.
If the same blank node is used more than once in the same RDF graph, it can be identified by a rdf:nodeID attribute. This identification is limited to the local graph. For example to express that John and Mary have a common friend, one can write.
vocabulary one will write.
...
111 Lake Drive
WonderCity
5555
Australia
...
For example to express that a person has at most one birth date, one will define the class "Person" as a subclass of an anonymous class of type "owl:Restriction". This anonymous class is defined by two attributes specifying the constrained property and the constraint itself (cardinality > 1)
1
Resource Description Framework
The Resource Description Framework is a family of World Wide Web Consortium specifications originally designed as a metadata data model...
, a blank node (also called bnode) is a node in an RDF graph representing a resource for which a URI
Úri
Úriis a village and commune in the comitatus of Pest in Hungary....
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
Notation 3
Notation3, or N3 as it is more commonly known, is a shorthand non-XML serialization of Resource Description Framework models, designed with human-readability in mind: N3 is much more compact and readable than XML RDF notation...
it is acceptable to use a blank node as a predicate. If a blank node has a node ID (not all blank nodes are labeled 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.
Example
"John has a friend born the 21st of April" can be written with two triples linked by a blank node representing the anonymous friend of John.ex:John foaf:knows _:p1
_:p1 foaf:birthDate 04-21
The first triple reads "John knows p1". The second triple reads "p1 is born on April 21st"
ex:John is a named resource, which means this resource is absolutely identified by the URI obtained by replacing the ex: prefix by the XML namespace it stands for, such as
_:p1 represents John's anonymous friend, not identified by a URI. One can know by the semantics declared in the FOAF
FOAF (software)
FOAF is a machine-readable ontology describing persons, their activities and their relations to other people and objects. Anyone can use FOAF to describe him or herself...
vocabulary that the class of _:p1 is foaf:Person.
RDF-XML Notation
In RDF-XML syntax a blank node can be represented by nested elements, such as the following.If the same blank node is used more than once in the same RDF graph, it can be identified by a rdf:nodeID attribute. This identification is limited to the local graph. For example to express that John and Mary have a common friend, one can write.
Representation of complex data
A blank node can be used to indirectly attach to a resource a consistent set of properties which together represent a complex data, such as a postal address. The different fields of the complex data are represented as properties attached to the blank node. For example in the RDF VCardVCard
vCard is a file format standard for electronic business cards. vCards are often attached to e-mail messages, but can be exchanged in other ways, such as on the World Wide Web or Instant Messaging...
vocabulary one will write.
...
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Anonymous classes in OWL
The ontology language OWL uses blank nodes to represent anonymous classes such as unions or intersections of classes, or classes called restrictions, defined by a constraint on a property.For example to express that a person has at most one birth date, one will define the class "Person" as a subclass of an anonymous class of type "owl:Restriction". This anonymous class is defined by two attributes specifying the constrained property and the constraint itself (cardinality > 1)