Rdf Primer / quote 47 of 55
The graph matters, not the notation
objects in RDF statements may be either URIrefs, or constant values (called literals) represented by character strings, in order to represent certain kinds of property values. Literals may not be used as subjects or predicates in RDF statements.
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So, for example, http://www.example.org/index.html appears three times (once in each triple) in the triples representation of the graph, but only once in the drawn graph. However, the triples represent exactly the same information as the drawn graph, and this is a key point: what is fundamental to RDF is the graph model of the statements. The notation used to represent or depict the graph is secondary.