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RE: Using two URIs for the same thing

From: Williams, Stuart <skw@hp.com>
Date: Sat, 18 Oct 2003 18:32:53 +0100
Message-ID: <5E13A1874524D411A876006008CD059F04A0788F@0-mail-1.hpl.hp.com>
To: "'Sandro Hawke'" <sandro@w3.org>
Cc: public-sw-meaning@w3.org

Hi Sandro,

I think the wording in the referenced part of the WebArch doc is probably
poorly expressed.

The intend of the wording (as I understand it) is that if your given a URI
for something (eg. with a representation, or out-of-band buy word of mouth
etc.) then you should make references with it as given. Don't expect minor
'spelling' variations work work (hence the oaxaca/Oaxaca example.

"Assigned" is probably the problem word... certainly the wording was not
trying to suggest that there is one true canonical assignment of a URI to a
given resource, only that if you 'obtain' for referring to a given resource,
then you should use it as obtained...

Does that help?


> -----Original Message-----
> From: Sandro Hawke [mailto:sandro@w3.org] 
> Sent: 16 October 2003 20:16
> To: public-sw-meaning@w3.org
> Subject: Using two URIs for the same thing
> I'm trying to do something totally reasonable with RDF and 
> the web, but I find myself going against a WebArch "good 
> practice".  How could I possibly do this better?  This smells 
> to me like a leak in WebArch notion of URIs, but I brought it 
> here because it's close enough to the hoses connecting 
> WebArch to RDF Semantics.
> We have four URIs:
>   (M1) http://www.w3.org/2002/03owlt/equivalentClass/Manifest003#test
>       This is what the WebOnt WG decided to name a particular OWL
>       test.  You, as a human or machine, can learn more about the test
>       by dereferencing the URI (doing an HTTP GET).  You should get
>       back some RDF/XML information about the test.  A nicely
>       formatted version of that information (plus some more you'd get
>       by following some more links) is at:
>   (H1) http://www.w3.org/TR/owl-test/L#equivalentClass-003
>       Meanwhile, I've been assembling an aggregation of results for
>       OWL tests.  As a human, today, you can visit 
>   (H2) http://www.w3.org/2003/08/owl-systems/test-results-out#test57
>       and see a row in a table about this test.   You'll see it's a
>       pretty easy one.  (Even my fairly-lame OWL reasoner passed it!)
>       That's also not a very stable fragment id.  Next week it might
>       land you on the results of another test.  Sorry.  But that's
>       part of what I'm trying to fix.
>       Mostly, though, I want to allow more varied views of the same
>       data.  I want to provide that data in RDF!  I think the right
>       approach is to use a URI like 
>   (M2) 
> http://www.w3.org/2003/08/owl-systems/test/equivalentClass-003#test
>       which can be used in RDF like M1, denoting the same test, but
>       which on dereference provides the test results data, along with
>       a triple saying it's owl:sameAs M1. [1]
> This seems reasonable, doesn't it?  Two names for the same 
> thing; when you follow them you get information about the 
> thing; you get different information when you follow 
> different names.  For some applications you'll use the first 
> name, for others the second.  There are other people building 
> test-results browsers; they should have access to the same data.
> Useful, practical, easy to do, and...  seemingly contrary to 
> TAG advice.  The current WebArch document says, "If a URI has 
> been assigned to a resource, Web agents SHOULD refer to the 
> resource using the same URI, character for character."  [2]
> So where is the breakdown here?
> Is this just the normal RFC 2119 escape from a "SHOULD": 
> "there may exist valid reasons in particular circumstances to 
> ignore a particular item, but the full implications must be 
> understood and carefully
> weighed before choosing a different course."   If so, I wish the
> document would spell this out better, saying what some 
> reasonable exceptions might be.
> It seems to me a lot like having two web pages about the same 
> topic. Surely that's not something Web Arch wants to warn against.  
> Maybe this is just a natural outgrowth of using URIs simultaneously as
> (1) logical constant symbols naming objects in some domain of 
> discourse and (2) network addresses naming virtual end-points 
> for communication.  Since we're using them in two ways at the 
> same time, they can be equivalent in one way, while being 
> completely different in
> another.   
>      -- sandro
> [1] Actually, I want to use 303-See-Other redirection instead of a
>     fragment URI, so I can merge in the human-readable view as well,
>     but that's orthogonal, so I'll pretend otherwise for now. 
> [2] 
> http://www.w3.org/TR/2003/WD-webarch-20031001/> #identifiers-comparison
Received on Saturday, 18 October 2003 13:35:21 UTC

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