Just require URLs

Jonathan Borden jborden at mediaone.net
Tue Jun 1 05:33:18 BST 1999

Carl Hage wrote:

> I think the URI identifying namespaces and DTDs should be URLs
> not URNs. An XML document without retrievable documentation on
> the DTD should be considered non-compliant.

By definition XML namespace URI's are URNs *not* URLs regardless of which
URI scheme/namespace they use.

Quoting from RFC 2396 (note that this supercedes the definition of URL!!!):

	A URI can be further classified as a locator, a name, or both.  The
   term "Uniform Resource Locator" (URL) refers to the subset of URI
   that identify resources via a representation of their primary access
   mechanism (e.g., their network "location"), rather than identifying
   the resource by name or by some other attribute(s) of that resource.
   The term "Uniform Resource Name" (URN) refers to the subset of URI
   that are required to remain globally unique and persistent even when
   the resource ceases to exist or becomes unavailable.


	A URN differs from a URL in that it's primary purpose is persistent
   labeling of a resource with an identifier.  That identifier is drawn
   from one of a set of defined namespaces, each of which has its own
   set name structure and assignment procedures.  The "urn" scheme has
   been reserved to establish the requirements for a standardized URN
   namespace, as defined in "URN Syntax" [RFC2141] and its related

Note that when the string "http://www.w3.org/xxx" is used as an XML
namespace URI this is a URN not a URL by definition (the scheme remains

Jonathan Borden

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