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

Re: homonym URIs (Re: What if an URI also is a URL)

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 12 Jun 2007 19:56:34 +0200
Message-Id: <6BF31555-F02C-4764-95CA-6316E4125183@cyganiak.de>
Cc: "Sandro Hawke" <sandro@w3.org>, semantic-web@w3.org
To: Pat Hayes <phayes@ihmc.us>


On 12 Jun 2007, at 18:21, Pat Hayes wrote:
> I'd like to see some evidence that punning me and my email address  
> is ever going to cause an actual problem, for that matter. Now,  
> punning, say, me and my wife, or me and my eldest son, *is* likely  
> to cause a problem.

To pick up just one point: Where do you draw the line between harmful  
punning and efficiency-increasing punning? Any rules of thumb for  
when it is OK? Why is it OK to pun with email addresses, but not with  


> But the appropriate thing to say is not to denigrate punning, but  
> to explain what is wrong with doing it badly.
>>>  And what about a URI
>>  > that I own and wish it to denote, say, the planet
>>>  Venus, or my pet cat? What do I do, to attach the
>>>  URI to my intended referent for it?
>> You publish a document (an ontology) so it's available through  
>> that URI.
>> If it's a hash URI, you publish the ontology at the non-hash version.
>> If it's a slash URI, you publish the ontology at the far end of a 303
>> redirect.  And you content-negotiate HTML and RDF.
>> So when users paste that URI into their browser, they get the  
>> official
>> documentation about it.
> None of that attaches a URI to my cat (though see below)
>> And when RDF software dereferences that URI, it gets some logical
>> formulas which should be understood (like the HTML) to be asserted  
>> by the
>> URI's owner/host/publisher.  Those formulas constrain the possible
>> meanings of that URI, relative to other URIs.
> Neither does any of that (and in this case, I can *prove* it, using  
> Herbrand's theorem.)
>>  They can't nail a URI to
>> Venus
> Quite. In fact, none of this can nail a URI to ANYTHING other than  
> something accessible using a transfer protocol.
>> , but they can use other ontologies to provide useful (and possibly
>> very constraining) information, like that it's an astronomical  
>> body with
>> a mass of about 5e+24kg.
> You are begging the question. Suppose an ontology asserts
> ex:Venus rdf:type ex:AstronomicalBody .
> Now, what ties that object URI to the actual concept of being an  
> astronomical body? And so on for all the other URIs in all the  
> other OWL/RDF ontologies. The best you can do is to appeal to the  
> power of model theory to sufficiently constrain the interpretations  
> of the entire global Web of formalized information. But that  
> argument from Herbrand's theorem (basically, if it has a model at  
> all then it has one made entirely of symbols) applies just as well  
> no matter how large the ontology is.
> The only way out of this is to somewhere appeal to a use of the  
> symbolic names - in this case, the IRIs or URIrefs - outside the  
> formalism itself, a use that somehow 'anchors' or 'grounds'  them  
> to the real world they are supposed to refer to. If we all assume  
> that English words are so grounded (not a bad assumption) then this  
> can be done in principle by using the URI in English sentences or  
> to other kinds of representation which are widely accepted as real- 
> world identifiers, like SS numbers or facial images. I did all  
> three in
> http://www.ihmc.us/users/phayes/PatHayes.html
> If the TAG said this somewhere, and recommended how to do it, that  
> would be great.
>> My advice here is, I confess, not widely followed.  But I hear  
>> more and
>> more people converging on the idea that this is both practical and
>> likely to be sufficiently effective.
> I agree. Still, its important to describe it properly. It doesn't  
> mean that URIs have a unique denotation.
>>>  The point surely is that URIs used to refer (not
>>>  as in HTTP, but as in OWL) do *not* have a
>>>  standardized meaning. Standards are certainly a
>>>  chore to create, but they only go so far. OWL
>>>  defines the meanings of the OWL namespace, but it
>>>  does not define the meanings of the FOAF
>>>  vocabulary,
>> No, that's up to the owner(s) of the FOAF terms.
>>>  or the URIrefs used in, say,
>>>  ontologies published by the NIH or by JPL.
>> And that's up to the NIH and JPL, respectively.
> I understand that. I was reacting to Tim's comments, which seemed  
> to suggest that all this should be determined by standards-setting  
> groups.
>>>  The
>>>  only way those meanings can be specified is by
>>>  writing ontologies: and finite ontologies do not
>>>  - cannot possibly - nail down referents
>>>  *uniquely*.
>> Ah -- there we go.  There must be a long history of this subject in
>> philosophy.  Can things ever be nailed down uniquely?  I haven't a  
>> clue.
>> But that's the wrong question.
> Surely this is exactly the question. I didn't raise the issue, Tim  
> did. There is a claim, often repeated and sometimes cited as  
> doctrine, that a URI *must* identify a *single* referent. To do  
> this requires that things are nailed down uniquely (isn't that  
> EXACTLY what it says?) but they can't be.
>>  In this thread, I don't think we're
>> talking about whether we can really be sure what we mean when we say
>> such a URI denotes Venus.
> Well then don't SAY that is what you are concerned with, for  
> goodness's sake. That is what is implied by "the URI for Venus has  
> a unique denotation".
>>  Instead, we're talking about whether it's a
>> good practice to use a single URI to denote clearly distinct things
> Aaaaargh. What do you think is 'clearly' distinct?
> The second rock from the sun might be a continuant or an occurrent.  
> Those are as clearly distinct as a rock and a Roman goddess. I know  
> people are a lot more familiar with the second kind of clearly  
> distinct, but ontologies aren't people. And the first kind of  
> difference is more important, if anything, than the second, for an  
> ontology. The second kind of muddle is easily resolved. The first  
> kind can be fatal.
>> ,
>> such as:
>>    (1) the second rock from the sun
>>    (2) the Roman goddess of love
>>    (3) a star tennis player
>>    (4) ... etc
>> The term "ambiguity" covers both these issues, but we don't need to
>> combine them.
> Well, you tell me how to distinguish them, then.
>>  The first is a kind of imprecision, a fuzziness
> No, its worse than that. Its like the distinction between an object  
> and a process. Fuzziness/imprecision is what gives you the  
> 'Everest' kind of examples.
>> , while
>> the second is the re-use of a word for a second meaning, a homonym.
>> (Homonyms seem to be called "overloading" in computer programming.)
>> I think we know how to work with homonyms, but since we're  
>> engineering a
>> new system, it seems like a good design decision to forbid them,  
>> doesn't
>> it?
> Well, actually, no. Overloading is widely used for good engineering  
> reasons. And on an open system like the Web, we arent going to be  
> able to prevent it happening, so we will need to have methods of  
> dealing with it. Once those are deployed, one might as well take  
> advantage of them. Making grand statements about what should be  
> done seems to me like trying to tell evolution what it ought to be  
> doing.
> Pat
> -- 
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Received on Tuesday, 12 June 2007 17:57:24 UTC

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