Set of subject→predicate→object-based statements that is grouped by predicate.
One can accurately refer to the RDF statement (triple), { <#Bob>
<http://xmlns.com/foaf/0.1/knows> <#Alice> . } as a representation
of a relation identified by the IRI <http://xmlns.com/foaf/0.1/knows>
that has a subject identified by the IRI <#Bob> and an object identified
by the IRI <#Alice>.