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Re: Comments on draft-hollenbeck-ietf-xml-guidelines-02.txt

From: Tim Bray <tbray@textuality.com>
Date: Tue, 30 Apr 2002 12:15:07 -0700
Message-ID: <3CCEED3B.6080107@textuality.com>
Cc: ietf-xml-use@imc.org, www-tag@w3.org
Michael Mealling wrote:

>>  http://www.textuality.com/tag/Issue8.html
>>To summarize the case against URNs: It's good for namespace documents 
>>exist, and it's good for them to be available, and most people can't 
>>dereference URNs.  -Tim
> But doesn't all of that depend on the application? Let's assume that
> the CNRP group updated the CNRP specification and made it into
> a namespace. The IETF has been pretty much opposed to putting 
> document locations like that in standards (for good reasons that
> some in the W3C might disagree with). The CNRP Working Group would
> use a URN as a way to ensure that the name _NOT_ be dereferenced
> through the IETF or IANA web sites but instead through some local
> catalog/EntityResolver.

So if I don't have one handy, as most people don't, I'm going to have to 
do some real work to track down the documentation.  Why is this better?

> I.e. we want to use URNs specifically because they're not usually
> dereferenced and we have good and valid reasons for not wanting to do that.

OK, we agree, if you explicitly don't want people to dereference the 
names, then using URNs is appropriate.  Our experience has been that 
dereferencing the names to get explanatory material is very helpful, but 
perhaps that experience is not relevant in this domain.

> Hmm.... looking at your document the logic used to get to the idea that
> URNs are bad for Namespace names is kind of circular. You assume that
> since a large portion of people use 'http:' scheme namespace names that
> those users might think they are retrievable. Since there is that
> assumption then we should all use 'http:' scheme names.

It's simpler than that.  People picked the http: names first, then 
thought they might as well put something there, and that turned out to 
be useful.  Since it turns out to be useful, we conclude that http: 
names are the way to go.

>  What if 
> I _DON'T_ want the namespace name to be resolvable
> by a conscious decision?

Then use a URN.

> Even still you also assert that namespace names aren't frequently dereferenced 
> at run-time. So the value of saying URNs are bad is even less evident.
> Either they're dereferenced or they're not....

There are two cases in which we see them being dereferenced: (1) by a 
human wondering "what is this namespace about?" or "I thought I knew 
this stuff, what the hell is a <cnrp:x35> tag?" - this doesn't happen at 
run-time.  (2) by an application at run-time - this isn't something I 
care about much but the SemWeb people are all excited about it.  I agree 
that run-time dereferencing would be really unlikely at the protocol level.

> I guess for me (and many on the URI-IG Group) the question comes down to this:
>  are URIs generic for the web or not?

URNs and what we used to call URLs are far from equivalent in their 
design goals and usage characteristics.  Is it not reasonable to assert 
that for certain application classes, one side or the other is a better 

> P.S. I though the TAG was going to defer to the URI group URI related 
> issues? At least that's they way it was represented to me....

It increasingly seems like *everything* is a URI-related issue.  Only 
half kidding. -Tim
Received on Tuesday, 30 April 2002 15:15:34 UTC

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