# Re: Why URN is a subset of URL

Peter Deutsch (peterd@bunyip.com)
Thu, 6 Oct 1994 09:33:21 -0400

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    Message-Id: <9410061333.AA09997@expresso.bunyip.com>

    From: Peter Deutsch <peterd@bunyip.com>

    Date: Thu, 6 Oct 1994 09:33:21 -0400

    In-Reply-To: "Jon P. Knight"'s message as of Oct  6,  8:50

    To: "Jon P. Knight" <J.P.Knight@lut.ac.uk>,

            "Roy T. Fielding" <fielding@avron.ICS.UCI.EDU>

    Subject: Re: Why URN is a subset of URL

Me again,

[ You wrote: ]

> On Wed, 5 Oct 1994, Roy T. Fielding wrote:
> > Peter Deutsch wrote:
> > > Still, the point is that at its heart, a URN is not
> > > intended to allow access but location independent naming.
> > > Just as ISBNs and library call numbers are different
> > > things and serve different purposes, I submit that URNs
> > > and URLs are different things and will serve different
> > > purposes.
> >
> > That is an implementation detail.
>
> Hmm, I'm not so sure. I think that the fact that URLs and URNs may have
> similar syntax _is_ an implementation detail, but the semantics are
> _defined_ to be different and its the semantics that are really the
> important thing (I think its also what Peter was probably getting at).

Was it Oscar Wilde who said "I could have made this
shorter, but I didn't have time"? ;-)

Seriously, you have hit the nail on the head here. The
semantics are different, thus I claim they are different.
At what philisophical level this difference exists is left
as an exercise for the reader.

For those who see no difference between URLs and URNs, you
are free to not use URNs, or treat them as the same thing.
As far as I can tell, this will mean that you will have a
class of identifiers which can not be used for access. I
can _not_ take what I call a URN and use it to access a
copy of a resource on the net. If I give one to Mosaic, it
will fail (unless you use Michael Mealling's modified
Mosaic, which recognizes URNs, performs an automatic
dereference and then presents the user with a set of URLs
to choose from).

> URLs are resource _locators_; URNs are _location_ independent names. How
> something which is location independent can be a member of a subset of a
> set of locators is a little beyond me at the moment.

Ditto. For those who claim they don't need these, no
sweat. I certainly see a need and we plan to deploy them
soon. Those who don't want them are free to ignore them.

- peterd

    --
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