Re: Proposal: 'tag' URIs

Thanks for all your thoughtful comments, Michael.   One thing I want
to ask about before hopping on a plane to WWW10:

> > There are lots of "arbitrary" URIs not using URN syntax, like
> > "mid:" and "data:".  Are those historical anomolies, which really
> > should have been URNs?  
> 
> For those of us who use URNs, probably. But we're not going to make
> a huge stink about it. They're all URIs and thus exist in the same
> 'layer' of the web and have the same very basic semantics.
...
> URNs do more than that. Infrastructure and systems are being deployed
> now that provide all sorts of things for URNs (and URIs in general).
> For example, we're setting up a URN based service called a Personal
> Internet Name which is a permanent name for a individual or organization.
> The ISBN organization is in the process of registering a URN for
> all ISBN numbers...
...
> And that's why we have URNs. Its a framework within which you can
> define your own namespace but which defines a more specific set of
> semantics (persistence, location independence, etc) than URIs in the general
> case. 

What's the advantage of having URNs be syntactically distinct from
non-URN URIs?  It made sense in the days when more people thought URLs
and URNs were really different beasts, but now that we seem to
understand differently -- as you say the infrastructure really applies
to URIs in general -- who (which peice of software) needs to know if a
particular URI has URN semantics.

I'm fine with "tag:" being a URN scheme if I see some practical use for
those extra four characters.

Or...  Hmm.  I don't want tags to have ANY semantics.  You're saying
URNs are presistent and location independent -- that urn:x always
denotes the same object regardless of the time and place of
interpretation, right?  Hrm.  What if we want a term
(tag:sandro@w3.org/1-4-27/you) which, when used in a message, denotes
the recipient of the message.  The term denotes a different recipient
if the same message is transmitted again, to someone else.  That can
be a tag URI.  Can it be a URN?  

(There's a weirdness here between denoting the recipient and denoting
the concept of denoting the recipient.   I'm trying to do the former;
URNs could clearly do the latter, which might be sufficient for all
applications.)

    -- sandro