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Re: uri, urn and info

From: Ray Denenberg, Library of Congress <rden@loc.gov>
Date: Fri, 10 Oct 2003 15:57:05 -0400
Message-ID: <053a01c38f68$ae08f820$849c938c@lib.loc.gov>
To: "Hammond, Tony (ELSLON)" <T.Hammond@elsevier.com>, "'Larry Masinter'" <LMM@acm.org>, <uri@w3.org>
Cc: "Ray Denenberg (home)" <raydenenberg@starpower.net>

From: "Hammond, Tony (ELSLON)" <T.Hammond@elsevier.com>
>
> > There is no requirement that URN namespaces have 'persistence of
> > identifiers as a primary purpose'.
>
> The above statement conflicts with this opening passage from RFC 2141:
>
> "Uniform Resource Names (URNs) are intended to serve as persistent,
> location-independent, resource identifiers."
>
> So, again we are left feeling really confused. Maybe it's just the words
> that are being used.

Yes, specifically: "persistent".  If we're discussing whether 'info' should
be a uri scheme or a urn namespace, and if that discussion relies on the
concept of persittence, then that discussion should be based on a common
definition of persistence, at least within the context of identifiers.

RFC 1737 says:
"Persistence: It is intended that the lifetime of a URN be permanent. That
is, the URN will be globally unique forever, and may well be used as a
reference to a resource well beyond the lifetime of the resource it
identifies or of any naming authority involved in the assignment of its
name."

(Of course that was 1994; is there a more current definition?)  Can someone
tell me if that's a meaningful definition of persistence (for purposes of
this discussion)?

If I were to analyze it, my first observation would be that "globally
unique" wasn't intended, and "globally unambiguous" was intended instead.
(Otherwise the definition makes no sense to me.)

Assuming so, that seems to break down to two requirements:
(a) an identifier, once assigned (within a namespace), won't ever be
assigned again (within that namespace); and
(b) it will be bound to the resource even beyond the lifetime of the
resource.

Clearly the identifiers we're talking about meet requirement (a).   But is
(b) a meaningful requirement?

An LCCN certainly meets requirement (a).  But (b)?  An LCCN identifies a
bibliographic record.  If that bibliographic record is deleted, what does it
mean to fulfill requirement (b)? That when someone tries to follow that
LCCN, they would be informed "LCCN 99-123456 used to be assigned to the
bibliographic record for book xyz, but that record no longer exists"?   If
they get "record not found" then the identifer is not persistent?

--Ray
Received on Friday, 10 October 2003 15:57:41 UTC

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