Re: URI: Name or Network Location?

Rdf was designed to help us annotate in a machine readable format resources
on the web, in particular, resources available over Hypertext Transfer
Protocol(HTTP) services.  The URI scheme http:// is the most common scheme
for identifying resources in the realm of the web.  I presume the info URI
scheme begins to accommodate those resources that have not fallen naturally
into some namespace on the web.  I don't think a URI has any bearing
whatsoever on the actual location of a resource it is describing.  In Rdf we
are free to use or make up any valid URI scheme.  The URL on the other hand
gives us a locator - so that a machine understands what protocol and what
address under that protocol a resource can be retrieved.  You should be able
to prod a URL with the appropriate technology and get a response.  I think
RSS 1.0 does a good job of both clarifying and confusing the separation of
URI and URL.  A channel has a link which must be a URL, whereas an image has
a rule that one is to use the about URI as also the URL of the image itself.

Section 1.2 of a URI rfc is also helpful [1] when thinking about the
interpretation of URI and URL.

My opinion is that if you want to reference the location of something, then
add some structures to your Rdf, e.g. through a property, that allows an
unambiguous interpretation.



----- Original Message ----- 
From: "Patrick Stickler" <>
To: "ext Phil Dawes" <>
Cc: "Hammond, Tony (ELSLON)" <>;
Sent: Wednesday, January 28, 2004 9:09 PM
Subject: Re: URI: Name or Network Location?

> On Jan 27, 2004, at 05:46, ext Phil Dawes wrote:
> > Hi Tony,
> >
> > Nobody else has answered this, so I'll have a stab.
> >
> > Hammond, Tony (ELSLON) writes:
> >>
> >>> I simply can't fathom any real benefit to having a URI
> >>> which, by definition, cannot be used to access such knowledge.
> >>
> >> The reason is to keep the barrier to entry as low as possible. By
> >> explicitly
> >> excluding dereference we have devised a very simple, focussed
> >> registration
> >> mechanism which requires almost zero maintenance and is consistent
> >> across
> >> the whole INFO namespace with a predictable behaviour (i.e.
> >> disclosure of
> >> identity). This is a baseline service - think of it as something like
> >> the
> >> Model T.
> >>
> >> I agree that it would be useful to have resource representations
> >> sitting out
> >> there on some network endpoint - but that is just way too expensive
> >> for the
> >> namespaces we are interested in fostering. There are no (human)
> >> resources
> >> available to maintain such an undertaking. The conclusion is that we
> >> either
> >> go this zero-resolution route or we accept that many of these
> >> namespaces
> >> will continue not to be represented on the Web. Which means that we
> >> will
> >> continue to be frustrated by not being able to 'talk' about well-known
> >> public information assets in Web description technologies.
> >>
> >
> > At work we've been using tag uris for the last 6 months in our
> > internal RDF knowledge base (which is still reasonably small: ~50000
> > triples), for much the same reason as the info URI scheme was created
> > - that we wanted to represent abstract concepts and physical things
> > without the dereference baggage and confusion.
> >
> > However, I've recently been convinced by Patrick's and Sandro's
> > arguments for using http uris to denote abstract concepts. It gives us
> > more flexibility in the future, for practically no cost.
> > (The fact that Sandro was one of the inventors of the tag uri scheme
> > give his arguments additional weight.)
> >
> > We are in the process of transitioning thus:
> >
> > I've registered a subdomain (call it for illustrative
> > purposes), and put a static html page up there which explains that
> > this URI space is for abstract URIs used on the semantic web.
> > Job Done.
> >
> > Now anybody who attempts to resolve a URI
> > (e.g. gets a
> > web page explaining that this uri represents an abstract concept or
> > physical object on the semantic web.
> >
> > This sorts out the initial confusion that relates to using http URIs
> > for abstract things, since anybody who is confused is most likely to
> > try to resolve the http URI in an HTML web browser.
> >
> > So the cost is one webpage (plus a bit of webserver config), and a DNS
> > subdomain entry.
> >
> Precisely.
> > Does this make sense
> Absolutely.
> > or am I missing something?
> Nope.
> This is exactly how I personally think it should be done.
> Though I'd go one step further (eventually, even if not at first) and
> make that server URIQA enlightened, so that, for those resources which
> have RDF descriptions, if folks dereference the URI, they get a metadata
> description of the resource, rather than just a boilerplate response.
> E.g., when you do an HTTP GET on
> there is no "typical" representation available for that resource, so
> the URIQA enlightened server falls back to trying to provide a
> description of that resource. If there weren't any description either,
> it would return a 404 response (or could return a friendly boilerplate
> response such as you describe above) but in this case, there is a
> description
> so it returns the description as the representation (which it is).
> If there *were* some other representation provided for typical GET
> requests, you could still obtain that description either using MGET
> or via a direct request to the portal.
> But as a first step (or even only step) the approach you've adopted
> is IMO the way to go, and leaves the door open to adding functionality
> in the future.
> Cheers,
> Patrick
> --
> Patrick Stickler
> Nokia, Finland

Received on Thursday, 29 January 2004 00:17:18 UTC