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.
Take the ISBN system for uniquely identifying books as an example of the use of typical URNs. The ISBN 0970639678 (urn:isbn:0-9706396-7-8) cites unambiguously a specific edition of NetLingo The Internet Dictionary. In order to gain access to this object and read the book, one would need its location: a URL address. A typical URL for this book on a Unixoperating system might look like the file path file:///home/username/NetLingoBook.pdf, identifying the electronic book saved in a file on a local hard disk. Therefore URNs and URLs have complementary purposes.