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

Michael Mealling (
Fri, 24 Oct 1997 21:10:13 -0400 (EDT)

From: Michael Mealling <>
Message-Id: <>
Subject: Re: The UR* scheme registry, Citing URL/URI specs
In-Reply-To: <> from Tim Bray at "Oct 24, 97 05:08:27 pm"
To: (Tim Bray)
Date: Fri, 24 Oct 1997 21:10:13 -0400 (EDT)

Tim Bray said this:
> At 06:11 PM 24/10/97 -0500, Dan Connolly wrote:
> >So if the URL/URN distinction is that way, please, PLEASE
> >show me! Please give an example where the use of the
> >term URN vs URL vs URI in the HTML, HTTP, XML, or RDF
> >specs will break things. 
> I don't think Dan was asking me, but

(Nor me but I had to jump in eventually! ;-)

> 1. if the XML spec says URL and somebody sends me a doc with an 
>    external reference to urn:ietf:rfc:1661 I probably won't be
>    able to resolve it, but at least I have some self-defense because 
>    I can make a strong case that it's not a URL, so I can tell the 
>    sender he's not XML-conformant.

What's the difference between that and getting an unknown URL scheme
like foo: which has only recently been identified or is an
experimental scheme?

> 2. If the XML spec says URI and the same thing happens, then I have no 
>    defense, because the sender can say "That's a URN, and a URN is a 
>    URI, and the spec says I can give you URIs."  I.e. conformance 
>    without interoperability.

Even if you limit it to URL the sender can give you things you don't
know about and call them URLs. Unless you application can programatically
keep up with the IANA's URL registry.

> I think this qualifies as breakage as a direct result of using URI
> rather than URL, but then I'm simple-minded.

I see no difference other than XML saying whether or not to support
a particular class of schemes.


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