Re: [URN] About realtive URNs

Ron Daniel, Jr. (rdaniel@lanl.gov)
Thu, 01 May 1997 09:33:05 -0600


Message-Id: <3.0.32.19970501093256.009c2970@cic-mail.lanl.gov>
Date: Thu, 01 May 1997 09:33:05 -0600
To: Daniel LaLiberte <liberte@ncsa.uiuc.edu>
From: "Ron Daniel, Jr." <rdaniel@lanl.gov>
Subject: Re: [URN] About realtive URNs
Cc: "URN Workgroup" <urn-ietf@bunyip.com>, uri@bunyip.com

At 10:01 AM 5/1/97 -0500, Daniel LaLiberte wrote:
>Ron Daniel, Jr. writes:

> >   1) Unambiguous determination of the base URN
>
>No problem.

I wish I shared your faith on this Dan. However, I'm uneasy about
it.
 
>the default
>base URI for a document, if not specified by the document or the
>delivery package of the document, is the last URI known by the client
>in accessing the document,

But this only works if resources that refer to each other using relative
links are migrated together. There are several reasonable scenarios where
this will not hold:
1)  The owner of a set of such resources sells 1/2 of them to another
    party, who takes charge of their storage. Now, 1/2 of the relative
    links will have the wrong base if it is determined using the "last
    URI known by the client" rule.
2)  Automated replication mechanisms spring up, and the most popular
    resource in an interlinked set gets widely replicated while less
    frequently used ones are not replicated.

>If a URN is redirected to a URL, and the URL is
>resolved to a document containing relative URIs, then they are
>relative to the URL (if the base is not otherwise specified), not the
>URN.

Right, and this can break in the two scenarios I mentioned above.

I'm more in favor of explicit determination of the base URI, either
by the BASE tag in HTML or the "destination" field mentioned in the
message yesterday. But here I think we have to be very careful to
say that only one BASE tag is allowed. People may associate any
number of identifiers with a work, only one of which will make the
relative URNs function correctly.


Ron Daniel Jr.              voice:+1 505 665 0597
Advanced Computing Lab        fax:+1 505 665 4939
MS B287                     email:rdaniel@lanl.gov
Los Alamos National Lab      http://www.acl.lanl.gov/~rdaniel
Los Alamos, NM, USA, 87545