Relationship To URL and URN
URIs can be classified as locators (URLs), as names (URNs), or as both. A uniform resource name (URN) functions like a person's name, while a uniform resource locator (URL) resembles that person's street address. In other words: the URN defines an item's identity, while the URL provides a method for finding it.
The ISBN system for uniquely identifying books provides a typical example of the use of URNs. ISBN 0-486-27557-4 (urn:isbn:0-486-27557-4) cites, unambiguously, a specific edition of Shakespeare's play Romeo and Juliet. To gain access to this object and read the book, one needs its location: a URL address. A typical URL for this book on a Unix-like operating system would be a file path such as file:///home/username/books/, identifying the electronic book library saved on a local hard disk. So URNs and URLs have complementary purposes.
Read more about this topic: Uniform Resource Identifier
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