W3C home > Mailing lists > Public > semantic-web@w3.org > September 2007

Re: What if an URI also is a URL

From: Reto Bachmann-Gmür <rbg@talis.com>
Date: Fri, 14 Sep 2007 00:16:08 +0200
Message-ID: <46E9B6A8.5070909@talis.com>
To: Richard Cyganiak <richard@cyganiak.de>
CC: Edward Bryant <edward.bryant@gmail.com>, semantic-web@w3.org

Richard Cyganiak wrote:
> ...
> Well, I'd say that the content provider acts against his own interests
> if he publishes the same representation at both these URIs.
> It's a good practice to explain the nature of the resource somewhere
> within the representation. So somewhere in the first one from your
> example there might be the text
> “This is the archived weather report of 13 September 2007 for the city
> of Bern, Switzerland.”
> while in the second one we might find
> “This is the current weather report for the city of Bern, Switzerland.”
> Or some equivalent RDF triples if we talk about Semantic Web content.
That's not always possible. An example are content-negotiated resource,
the following URIs all identify something else:


But you may (depending on your Accept and Accept-Language headers) get
the same representations for all of them.
> In the absence of such an explanation, an agent has little hope to
> find out what he's looking at. He cannot use the URI to reliably refer
> to anything, because he doesn't know what it will return tomorrow.
> Bookmarking it, linking to it, or passing it on to someone else,
> becomes a perilous affair. After all, I'd really like to know if I'm
> looking at today's or yesterday's weather report. A weather report
> that doesn't give me that information won't be popular.
Certainly it would be nice to a have a technology that allows the client
to bookmark different "level of abstractions", e.g. having the browser
ask you if would you like to bookmark "Today's weather in Bern",
"Today's weather in Bern /English Version", "The weather in Bern on
2007-09-13" and so own.
> Thus, both content consumer and content provider benefit from
> representations that explain the nature of the resource.
> A second, less helpful choice would be external information about the
> resources. For example, there might be an RDF file or HTML file at
> <http://Example.org/weather/> that tells us what all the individual
> URIs refer to.
And you may find two contradicting graphs on different locations and the
only thing you know is that at least one of them is wrong :-)


Reto Bachmann-Gmür
Talis Information Limited

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Received on Thursday, 13 September 2007 22:15:55 UTC

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