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Is a string of characters used to identify a name of a web resource. It is defined in section 3 of http://tools.ietf.org/html/rfc3986#section-3. An example of a URI would be "http://purl.org/dc/elements/1.1/".
Universally
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Unique Identifier (UUID)
A "practically" unique identifier that is used to identify a node. For more detailed description see wikipedia.
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