RE: Next steps on draft-zigmond-tv-url-02

From: Harald Tveit Alvestrand (
Date: Wed, Sep 01 1999

Message-Id: <>
Date: Wed, 01 Sep 1999 07:53:49 +0200
To: Patrick Schmitz <>,, Dan Zigmond <>,
From: Harald Tveit Alvestrand <>
Cc:, Dean Blackketter <>
Subject: RE: Next steps on draft-zigmond-tv-url-02

At 16:20 31.08.99 -0700, Patrick Schmitz wrote:

>I should have said that more carefully...  A URI definition does not
>necessarily imply that there is a document at the location; a URL does.  The
>corresponding http: URL may or may not exist, as noted.

actually.....not quite. From RFC 2396:

1.2. URI, URL, and URN

    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.

They both name "resources"; an URL also names at least one access mechanism.

          A resource can be anything that has identity.  Familiar
          examples include an electronic document, an image, a service
          (e.g., "today's weather report for Los Angeles"), and a
          collection of other resources.  Not all resources are network
          "retrievable"; e.g., human beings, corporations, and bound
          books in a library can also be considered resources.

          The resource is the conceptual mapping to an entity or set of
          entities, not necessarily the entity which corresponds to that
          mapping at any particular instance in time.  Thus, a resource
          can remain constant even when its content---the entities to
          which it currently corresponds---changes over time, provided
          that the conceptual mapping is not changed in the process.

Believe me, the number of emails required to get agreement on that 
definition was QUITE horrendous!

                           Harald A

Harald Tveit Alvestrand, Maxware, Norway