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

From: Rikkert Koppes <rikkert@finalist.com>
Date: Wed, 13 Jun 2007 11:42:30 +0200
Message-ID: <466FBC06.4040400@finalist.com>
To: Richard Cyganiak <richard@cyganiak.de>
CC: Pat Hayes <phayes@ihmc.us>, Sandro Hawke <sandro@w3.org>, semantic-web@w3.org

What you do is wrong, it was my problem as well. You just can't use the 
same identifier as both you and your webpage. You should do something like:

   <http://richard.cyganiak.de/#me> a foaf:Person .
   <http://ontoworld.org/wiki/Richard_Cyganiak#me> a foaf:Person

Rikkert Koppes (mophor)

Richard Cyganiak wrote:
> On 12 Jun 2007, at 22:07, Pat Hayes wrote:
>>> 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 wives?
>> Because people and email addresses are so different that almost 
>> nothing you ever want to say about or do to one is ever said about or 
>> done to the other. If you email to PatHayes, you must have meant to 
>> PatHayes' email address. If you assert that my email address has two 
>> children, you must have meant me. With two people (or two mailboxes) 
>> however, things are different. There really is no way to tell then 
>> which is meant: you can't locally disambiguate the punning.
> Here are two web pages about me:
>    <http://richard.cyganiak.de/>
>    <http://ontoworld.org/wiki/Richard_Cyganiak>
> One is in German, the other in English:
>    <http://richard.cyganiak.de/> dc:language "de" .
>    <http://ontoworld.org/wiki/Richard_Cyganiak> dc:language "en" .
> You say it's OK to use a web page URL to denote the person it's about, 
> so:
>    <http://richard.cyganiak.de/> a foaf:Person .
>    <http://ontoworld.org/wiki/Richard_Cyganiak> a foaf:Person .
> Both clearly denote the same person, so we can confidently state:
>    <http://richard.cyganiak.de/>
>       owl:sameAs <http://ontoworld.org/wiki/Richard_Cyganiak> .
> This allows us to conclude:
>    <http://richard.cyganiak.de/> dc:language "de" .
>    <http://richard.cyganiak.de/> dc:language "en" .
> Which is obviously wrong. So what did I do?
> 1. I used the DC, FOAF, and OWL vocabulary, which are used in exactly 
> this way all over the Semantic Web.
> 2. I used an inference rule sanctioned by the OWL specifications, 
> which is used all over the Semantic Web.
> 3. I used your claim that punning is OK.
> And I arrived at an incorrect conclusion. Why, Pat?
>> So the rule of thumb, which can be made operationally quite precise, 
>> is that punning is OK if (there is a very high probability that) 
>> there is enough contextual information available at the point of use 
>> to figure out which of the various meanings is intended.
> I think on the open Semantic Web, there is a very high probability 
> that your URI will end up in places where that contextual information 
> is not available and thus the information consumer cannot figure out 
> which of the various meanings was intended. It seems to me that, 
> following your own guideline, we'd have to conclude that punning on 
> the Semantic Web is almost never OK.
> Richard
>> Pat
>>> Cheers,
>>> Richard
>>>> 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
>>>> -- 
>>>> ---------------------------------------------------------------------
>>>> IHMC        (850)434 8903 or (650)494 3973   home
>>>> 40 South Alcaniz St.    (850)202 4416   office
>>>> Pensacola            (850)202 4440   fax
>>>> FL 32502            (850)291 0667    cell
>>>> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>> -- 
>> ---------------------------------------------------------------------
>> IHMC        (850)434 8903 or (650)494 3973   home
>> 40 South Alcaniz St.    (850)202 4416   office
>> Pensacola            (850)202 4440   fax
>> FL 32502            (850)291 0667    cell
>> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Wednesday, 13 June 2007 09:42:33 UTC

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