- From: Larry Masinter <masinter@parc.xerox.com>
- Date: Fri, 24 Oct 1997 11:46:25 PDT
- To: Al Gilman <asgilman@access.digex.net>
- CC: Dan Connolly <connolly@w3.org>, timbl@w3.org, fielding@ics.uci.edu, Harald.T.Alvestrand@uninett.no, moore@cs.utk.edu, uri@bunyip.com, lassila@w3.org, swick@w3.org, tbray@textuality.com, jeanpa@microsoft.com, cmsmcq@uic.edu, dsr@w3.org, lehors@w3.org, ij@w3.org, slein@wrc.xerox.com, jdavis@parc.xerox.com
I think that's a good summary of the situation. HTML and XML can say they use URIs, and then point to a W3C note that says "A URI is defined by IETF, currently it points to URLs, and there is some work on URNs". Here's a puzzle: A URN is a kind of a URL: One way to locate a resource is to name it. Of course, there's some assumption of a mechanism by which names can get looked up and turned into resource locations. A URL is a kind of a URN: One way to name a resource is with its location; "the thing that is located at X". It's not a very good name, but then, not all names are good in that role. Given both of these kinds of subsetting, it might be that the distinction between "URL" and "URN" is not in the protocol element (what's the syntax) but in the use. URNs are used for identification, while URLs are used for location. What are the criteria for use of URLs and URNs? Embedding in a document: It's reasonable for a persistent form of a document to contain its own URN, since the URN shouldn't change when the document gets replicated. It is bad design to require that a document contain its own URL (or its own BASE, for that matter), because it interferes with replication and transmission. Document elements contain relative URLs, though, since a tree structure of URLs actually form a kind of compound document, and the relative elements are used to identify the other compound parts. Larry -- http://www.parc.xerox.com/masinter
Received on Friday, 24 October 1997 14:47:24 UTC