W3C home > Mailing lists > Public > uri@w3.org > May 2001

Re: Proposal: 'tag' URIs

From: Michael Mealling <michaelm@netsol.com>
Date: Mon, 7 May 2001 17:33:28 -0400
To: "Simon St.Laurent" <simonstl@simonstl.com>
Cc: michaelm@netsol.com, Sandro Hawke <sandro@w3.org>, Tim Kindberg <timothy@hpl.hp.com>, uri@w3.org
Message-ID: <20010507173328.E23981@bailey.dscga.com>
On Mon, May 07, 2001 at 05:22:53PM -0400, Simon St.Laurent wrote:
> At 05:15 PM 5/7/01 -0400, Michael Mealling wrote:
> >On Mon, May 07, 2001 at 05:13:48PM -0400, Simon St.Laurent wrote:
> > > At 04:20 PM 5/7/01 -0400, Michael Mealling wrote:
> > > >Nope. URNs have the requirement that once you assign a URN to its
> > > >Resource you can never reassign that URN to some other Resource.
> > > >Sure, you could assign a URN to whatever the http protocol gave you
> > > >on port 80 at cnn.com and that would be a useful thing because then
> > > >I could rely on the fact that, no matter what CNN did to cnn.com or
> > > >whether or not CNN even existed anymore, whenever I used that
> > > >URN I knew that someone hadn't changed the meaning out from under me.
> > >
> > > So does this mean that changing the Resource is effectively creating a new
> > > Resource?
> >
>>Nope. URIs and URNs never define any concepts or operations that have
>>to do with the Resource other than the act of binding a URI/URN to one (which
>>is how a Resource comes into existence). The statement "changing
>>the Resource" has no meaning outside of some specific application that defines
>>what "change" means for that application space. Low level caching might
>>consider 'change' to be moving it from one IP address to another while
>>DAV might define it as a versioning event that doesn't care what IP
>>address it is currently at.
> I guess my concerns center on:
> >someone hadn't changed the meaning out from under me.
> I'm concerned about:
> a) how you find that meaning
> b) what "meaning" means in a resource context
> c) how changing a resource avoids changing said meaning

Ahh... probably a bad choice of words. What I meant to say is that someone
hadn't changed the binding to some other Resource. The http URI scheme
never says that reassignment is not allowed. Thus when things like
domain-names change or filesystems move, the binding is being intentionally 
changed to a new Resource. When I used the word meaning what I was
getting at was "the original binding". By disallowing reassignment, URNs
allow you to assume that the binding is never other than the original.


Michael Mealling	|      Vote Libertarian!       | www.rwhois.net/michael
Sr. Research Engineer   |   www.ga.lp.org/gwinnett     | ICQ#:         14198821
Network Solutions	|          www.lp.org          |  michaelm@netsol.com
Received on Monday, 7 May 2001 17:37:11 UTC

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