Re: [URN] Re: The UR* scheme registry, Citing URL/URI specs

Dave Raggett (
Mon, 3 Nov 1997 09:32:17 -0500 ()

Date: Mon, 3 Nov 1997 09:32:17 -0500 ()
From: Dave Raggett <>
cc: "Roy T. Fielding" <>, uri@Bunyip.Com,
Subject: Re: [URN] Re: The UR* scheme registry, Citing URL/URI specs 
In-Reply-To: <>
Message-ID: <>

On Thu, 30 Oct 1997 wrote:

> I would replace the above paragraph with the following argument
> for a non-technical distinction: 
>    A URN differs from a URL in that a URN is intended to remain
>    globally unique and persistent long after the resource it
>    refers to ceases to exist or becomes unavailable. 
> This non-technical distinction seems to agree with Keith Moore's
> argument that URNs are really for humans.

I am not sure this follows from your definition. For instance,
GUIDs are guaranteed to remain globally unique but need never
refer to any concrete resource, neither are they Human friendly
unless you are particularly good at remembering 128 bit numbers.

I think the key idea is that such names are guaranteed to be
globally unique over a very extended period of time -- i.e. they
won't be reused unintentionally for something different, as is
quite likely for names based on file system hierarchies. 

> We could leave it at that or add some further explanation, which
> perhaps gets too close to the controversy:
>    A URN should be associated with a global, persistent service
>    for resolving it or returning a redirection to another URI.

I don't think this is necessary in all cases. For example an MD5
of a document is useful even in the absence of such a service.
The uniqueness of a name over space and time certainly lends itself
to fault tolerant means to access resources associated with such
names. However this is a useful side-effect and not a fundamental


-- Dave Raggett <>
phone: +44 122 578 2984 (or 2521) +44 385 320 444 (gsm mobile)
World Wide Web Consortium (on assignment from HP Labs)