Elaborate Context URIs / rdfg:Graph in context of nanopublications

[csarven]

The recommendation should perhaps have a mini-section on context URIs in context of nanopublications. For instance:

• Why are they used or how are they utilized?
• It should also talk about deferenceable context URIs (URLs) vs. SPARQL named graphs (URIs) which typically can't be deferenced (e.g., see current Query Template)
• It might also be good to address what type of metadata may be useful to associate with the context URI.
• How will a nanopublication tool/parser interpret an RDFa dcoument with a nanopublication (specifically about using the document URL as the context URI)

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