Literals & Non-literals
Andy Powell wrote:
"So in Dublin Core metadata, each value is either "a literal" (a literal value) or "a physical, digital or conceptual entity" (a non-literal value) and the choice of which to use is largely one of convenience.
In the case of dc:subject, the value is the "topic" of the resource being described. The topic might be a concept ("physics"), a place ("Bath, UK") or a person ("Albert Einstein") or something else. While that topic could be treated as a literal value (and superficially at least, doing so may appear to be more convenient) good practice suggests that it is better if it is treated as a non-literal value, i.e. as a physical, digital or conceptual entity. Why? Because if the topic is treated as a non-literal value then it can be assigned a URI and can become the subject of other descriptions. If the topic is treated as a literal value then it becomes a descriptive cul-de-sac - no further description of the topic is possible.
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A literal may be the object of an RDF statement, but not the subject or the predicate."
[eFoundations Blog, "The importance of non-literals to linked data", 18 August 2008: http://efoundations.typepad.com/efoundations/2008/08/the-importance.html]