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Re: Proposal: 'tag' URIs

From: Sandro Hawke <sandro@w3.org>
Date: Fri, 27 Apr 2001 10:01:39 -0400
Message-Id: <200104271401.KAA11630@hawke.org>
To: "Roy T. Fielding" <fielding@ebuilt.com>
cc: Tim Kindberg <timothy@hpl.hp.com>, uri@w3.org

> Creating a specific URI scheme to do what can be done by any existing
> URI scheme (namely, allow an authority to define a unique name) is a
> total waste of time.

To our knowledge, no existing scheme meets our requirements.  If you
know of one which does, please let us know.  All the schemes we know
about do not work for us because they have have at least one of these
problems: 

   (1) significant administrative overheard 
   (2) no provision against unintentional conflicting reuse (such as
       when a domain name is re-assigned),
   (3) a limitation on the class of things which can be identified
       according to the specification (such as a mail message, for
       mid: identifiers),  or
   (4) a syntax which makes them impractical for humans to compare,
       remember, or type correctly.  

> ... you should use the URN syntax: at least
> then you will be arbitrary in the same way as the others. 

I don't see a reason for using URN syntax here, but perhaps I
misunderstand URNs.  The two kinds of reasons one might use URN
syntax, as I understand it, are philosophical and operational:

Philosophically, you can say "tags are really names".  But aren't all
identifiers really names?  Perhaps there is some distinction between
identifying things by qualities (like how you might find them) and by
some outside-the-system mapping between names and objects in a domain
(like the thing just has a name), but I don't know how that could
matter.  There are lots of "arbitrary" URIs not using URN syntax, like
"mid:" and "data:".  Are those historical anomolies, which really
should have been URNs?  I don't understand this line well enough to
figure out where mailto: should go.  It's just an arbitrary name for a
mailbox, right?

Operationally, the only reason I've seen for using URN syntax is that
it allows some browsers to potentially invoke some local database
lookup code to turn it into another URI (such as an http: one).  But
we don't want that.  If we wanted that, we would have used an http:
URI in the first place.

If you're going to argue that we really DO want that, then you're
getting into per-application territory.  Tim Kindberg can say why HP
Labs Cooltown doesn't want that.  I can say why it's a useful
experiment (at least) in design of semantic web components to keep
certain terms free of pre-defined semantics.  Other application may have
their own reasons.

     -- sandro

Sandro Hawke, sandro@w3.org
Research Scientist/Developer
W3C Semantic Web Activity
Received on Friday, 27 April 2001 10:04:02 UTC

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