Comparison With URLs
A URN is similar to a person's name, while a URL is like a street address. The URN defines something's identity, while the URL provides a location. Essentially, "what" vs. "where".
URNs are often compared to the ISBN system for uniquely identifying books (and in fact, it is possible to encode an ISBN as a URN). Having a book's unique identifier lets you discuss the book, such as whether you've read it, enjoyed it, etc. To actually read the book, however, you need its location (e.g., "on the bedside table"). So URNs and URLs are often complementary; for example, you might discuss an RFC using both concepts: "you can find urn:ietf:rfc:3187 (URN) over at http://tools.ietf.org/html/rfc3187.html (URL)."
Read more about this topic: Uniform Resource Name
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—Henry David Thoreau (1817–1862)
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