# URN Requirements

Jared_Rhine@hmc.edu
Sat, 14 May 1994 15:27:15 -0700

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    Date: Sat, 14 May 1994 15:27:15 -0700

    Message-Id: <199405142227.PAA27231@osiris.ac.hmc.edu>

    From: Jared_Rhine@hmc.edu

    To: avatar@notebook.aus.xanadu.com (Andrew Pam)

    Subject: URN Requirements

Andrew> One of the requirements I am contemplating in the Xanadu equivalent
Andrew> of URNs is that resources can be uniquely named on networks or
Andrew> machines not connected to each other, which may become connected at
Andrew> a later stage. [...] My question is, how would this model of URNs
Andrew> fit into the proposed URI system?

Poorly. Although interesting, I do not see a great deal of utility for
amount of hassle this would be. You can certainly organize naming authorities
regardless of their connectivity; what does your model buy us?

Andrew> In other words that the resource names must be unique without any
Andrew> knowledge of other names being assigned elsewhere, and with no
Andrew> central naming authority. [...] I believe that this could be
Andrew> implemented by ensuring that the resource identifiers are always
Andrew> stored relative to the local server, and are canonicalised
Andrew> immediately whenever transferred from another server.

I'm having trouble coming up with any "canonicalization" algorithm that
would work quickly and deterministically. Any comparision operation would
need to canonicalize both URNs, anyway (so a server can see if it has a copy
of an object cached locally); why not just store them in their canonical
form in the first place?

Without loss of generality, I think we can assume that something, somewhere,
must guarantee uniqueness. The URN requirements document leaves this rather
open, postulating "naming authorities", but no "central" authority. The URI
scheme could model what you suggest by calling each server a naming
authority, but such a scheme would horribly cripple other parts of the
model, including freedom to move objects around.

    --
    Jared_Rhine@hmc.edu | Harvey Mudd College | http://www.hmc.edu/~jared/

    "To hear many religious people talk, one would think God created the
     torso, head, legs and arms, but the devil slapped on the genitals."
            -- Don Schrader

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