Dave Viner's Weblog

Differentiating URIs, URLs, URNs (and the Semantic Web)

This note is by far the best I've ever read for clearly delineating the difference between URIs, URLs, URNs, "resources", and "representations". If you've looked at any stuff related to the Semantic Web, or read the REST thesis, or listened in on the REST vs SOAP discussions, or even used URNs, you've probably run across this distinction. This note does a superb job at defining and distinguishing what they all mean. It doesn't unlock the secrets of the semantic web, but having a clear understanding of these distinctions will greatly help you understand and participate in any discussions about rest or the semantic web.

http://www.ibiblio.org/hhalpin/homepage/notes/uri.html