W3C home > Mailing lists > Public > semantic-web@w3.org > May 2009

Re: URI lifecycle (Was: Owning URIs)

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 22 May 2009 12:47:21 -0500
Cc: Hugh Glaser <hg@ecs.soton.ac.uk>, semantic-web <semantic-web@w3.org>, Linked Data community <public-lod@w3.org>
Message-Id: <A7BA43A8-C658-4AFC-B35E-5E8B6C684ACF@ihmc.us>
To: David Booth <david@dbooth.org>

On May 20, 2009, at 12:01 AM, David Booth wrote:

> Hi Hugh,
> Re:
>>> "The URI Lifecycle in Semantic Web Architecture":
>>> http://dbooth.org/2009/lifecycle/
> On Tue, 2009-05-19 at 18:08 +0100, Hugh Glaser wrote:
>> Hi David,
>> Excellent stuff.
>> It is important, as you do, to make statements about what is good
>> citizenship, and to distinguish these from what might be enforced  
>> etc..
>> I was about to suggest that you might want a ≥URI is deprecated≤ in  
>> your
>> figure, but then I found that was the title of the Event 4 section
>> corresponding to ≥URI is obsolete≤. :-)
> Oops!  Thanks for catching that error.  I've fixed it now.
>> I suspect that this area could do with a bit of teasing out.
>> For example, your description may indeed be ≥obsolete≤, as it  
>> implies no
>> access possible, and should never be a deliberate action by the  
>> owner (I
>> suspect there might be another explicit part of URI owner  
>> responsibility 1,
>> which is to serve the URI declaration for as long as they are able,  
>> or
>> something like that). On the other hand, the owner may want to  
>> discourage
>> use of some URIs in preference to others, so this is a deliberate  
>> act by the
>> owner (I am thinking of opencyc in particular here), and this is  
>> the sort of
>> thing I would term deprecation.
> Yes, that's a good point.  I intended to include that case under the
> overall "URI is obsolete" section (since the point is that the URI
> should no longer be used to make new statements), but it looks like I
> forgot.  I've added it now.
>> It looks like an excellent research topic to provide theories and  
>> tools for
>> determining when the responsibilities are being broken.
>> A last comment, which I know we have discussed, and you possibly  
>> disagree:
>> "Community expropriation of a URI"
>> Might have meant something else.
>> One of the problems is that many authors will not discharge their  
>> Statement
>> Author Responsibilities, but will assume that the URI is the one  
>> they want.
>> Over time, this may mean that the general SW uses a URI in a way  
>> other than
>> the URI owner intends, to the extent that it becomes irrelevant  
>> what was the
>> original meaning (there are many parallels for this in natural  
>> language, and
>> indeed it is the social process that causes language to change).
>> [ . . . ]
> Yes, that's a great topic for discussion.  It is clear that semantic
> drift is a natural part of natural language: a word that meant one  
> thing
> years ago may mean something quite different now.

And the same is happening with URIs. My favorite example is dc:author,  
which when coined was intended to refer to the relation of authorship  
between people and things like books, things that would be found in a  
library catalog. But by now, thanks to FOAF, the overwhelmingly  
largest usage of dc:author is to state the relationship between a  
person and their FOAF home page. This is a real social meaning shift,  
and it happened without anyone really noticing and without anything  
breaking or failing to work. If the original DC specs had posted a  
detailed 'authoritative' ontology, the change would still have  
happened and it would still have worked, but there would have been  
interminable debates about whether a home page was really a "work" (or  
whatever the term that was used), suggestions that FOAF use a  
different URI, etc., etc.,, all to absolutely no purpose. Just look at  
the interminable and utterly pointless debate now raging about exactly  
what an 'information resource' *really is*, none of which has any  
bearing whatsoever on how the actual Web works, even though the latter  
is actually constructed almost entirely out of the former.

>  As humans we can
> usually deal with this semantic drift by knowing the context in  
> which a
> word is used, though it can cause real life misunderstandings  
> sometimes.
> However, I think our use of URIs in RDF is different from our use of
> words in natural language, in two important ways:
> - RDF is designed for machine processing -- not just human
> communication -- and machines are not so good at understanding context
> and resolving ambiguity; and
> - with URI declarations there is a simple, feasible, low-cost  
> mechanism
> available that can be used to anchor the semantics of a URI.

But that begs the question of whether you want them to be anchored. I  
suggest that we often don't: that letting them 'drift' in meaning to  
fit their usage is exactly what we want to be happening.

> In short, although semantic web architecture could be designed to  
> permit
> unrestricted semantic drift, I think it is a better design -- better
> serving the semantic web community as a whole -- to adopt an
> architecture that permits the semantics of each URI to be anchored, by
> use of a URI declaration.

And I disagree. I think this whole idea is based on the insistence of  
various authoritative sources upon the naive idea that URIs have to  
"identify" things. This has never been the case, in fact, even in the  
pre-Semantic web, and its even less the case now. Its a chimera:  
forget about it, rather than try to enforce it. What URIs do is fetch  
chunks of information. Hardly anyone using the normal Web in the  
normal way gives a damn what "thing" their URIs "identify": they only  
care about what they are looking at, which is whatever that "thing"  
sent back to them in the body of the 200 response, and what that means  
or what it can do. The very design of html is all about *hiding* the  
URIs from users, not about telling them what it is that URIs identify.


> For more explanation see: "Why URI Declarations? A comparison of
> architectural approaches"
> http://dbooth.org/2008/irsw/
> -- 
> David Booth, Ph.D.
> Cleveland Clinic (contractor)
> Opinions expressed herein are those of the author and do not  
> necessarily
> reflect those of Cleveland Clinic.

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Received on Friday, 22 May 2009 17:48:49 UTC

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