context of dc:identifier

I was wondering about the scope of identifier when using dc:identifier.
The definition quoted on http://www.w3.org/TR/rdf-primer/ is

    * *Identifier*: An unambiguous reference to the resource within a
      given context.

I was wondering what the "given context" might be when using
dc:identifier in an rdf-graph. Any suggestion on how to express or on
how to guess this context?

cheers,
reto

-- 
Reto Bachmann-Gmür
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