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RE: Which URI should be persistent when redirects are used?

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 27 Sep 2007 14:43:07 -0500
Message-Id: <p06230914c321b5e98d67@[]>
To: Misha Wolf <Misha.Wolf@reuters.com>
Cc: www-tag@w3.org

>OK.  The story is ...
>The IPTC is likely to approve the NewsML-G2 specification at our
>meeting in Prague in mid-October.
>We use URIs to denote concepts associated with the News Object (as
>values of Subject, Genre, Creator, Title, Publisher, etc).  We
>want these URIs to be invariant and to participate fully in the
>Semantic Web.

The key question, seems to me, is: who has the responsibility for 
creating these URIs and assigning them their meanings? Who 'owns' 
them? Because that agency has quite a task: it has to somehow tell 
the world, unambiguously, what exactly it is that these URIs denote. 
When that denoted thing can't be accessed by a Web server of some 
kind, that is quite a task. Does anyone have any idea how to do it? 
Suppose for example I am given the task of telling everyone that some 
URI, say http://myexample.notarealone/Jazz-X , is intended by me to 
denote Jazz. Well, I can say that, but what does it mean? What is 
Jazz exactly? Is it the totality of all jazz recordings? The 
boundaries of this set are not well-defined, but perhaps that does 
not matter (though I suspect it will); but maybe Jazz isn't such a 
neatly defined thing as a set in any case. How do I explain what Jazz 
is well enough so that others can use this URI in the way I intend?

Put the same point another way: how will anyone even know whether or 
not URI-X is invariant? I might say that my URI-X denotes Jazz and 
have one thing in mind, but if 99% of the people who use my URI in 
fact use it with a somewhat different notion of Jazz in mind, then 
that's what it will in fact denote when used on the Web, 
independently of my intentions. So, did the denotation change? Was 
the URI invariant?


>   If a receiving system uses HTTP to access
>information about a concept (such as Jazz, Marcel Marceau, Mona
>Lisa, Oil, Reuters), the system hosting the taxonomy in question
>may have multiple representations of the taxonomy, eg:
>-  IPTC Knowledge Item
>-  Web pages in various languages
>So let's say that Mona Lisa has the following URIs:
>-  the one used in News Objects
>-  the one which will deliver the RDF/XML
>-  the one which will deliver the Knowledge Item
>-  the one which will deliver the Simplified Chinese Web page
>-  the one which will deliver the Traditional Chinese Web page
>-  the one which will deliver the Japanese Web page
>-  the one which will deliver the International English Web page
>-  the one which will deliver the US English Web page
>-  etc
>One could then write a set of assertions along the lines of:
>-  URI-Y refers to the Simplified Chinese Web page describing URI-X
>And it would be a Good Thing if URI-Y were invariant.
>But (it seems to me that) it would be an even Better Thing if URI-X
>were invariant.
>The more invariance one demands of the hosting organisations, the
>more unlikely it is that it will be delivered.
>-----Original Message-----
>From: Dan Connolly [mailto:connolly@w3.org]
>Sent: 27 September 2007 15:02
>To: Misha Wolf
>Cc: W3C-TAG; semantic-web-ig list
>Subject: RE: Which URI should be persistent when redirects are used?
>On Thu, 2007-09-27 at 14:47 +0100, Misha Wolf wrote:
>>  How about 303 redirects?
>Well, reading the spec, I see "The new URI is not a substitute reference
>for the originally requested resource."
>which strongly suggests, to me, that both URIs should be persistent.
>>  And what about content negotiation?
>What about it?
>Could you elaborate on the question? What are you trying to do?
>>    The requestor's original
>>  URI could be redirected to different URIs depending on MIME
>>  Type and Language.
>>  Which of these many URIs would represent the resource for the
>>  SemWeb?
>"the resource"? which resource? Could you tell me the beginning
>of this story?
>Dan Connolly, W3C http://www.w3.org/People/Connolly/
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Received on Thursday, 27 September 2007 19:43:25 UTC

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