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owl:sameAs use/misuse/abuse Re: homonym URIs

From: Bernard Vatant <bernard.vatant@mondeca.com>
Date: Thu, 14 Jun 2007 12:56:17 +0200
Message-ID: <46711ED1.4080409@mondeca.com>
To: semantic-web@w3.org

Just to hit this owl:sameAs (ab)use nail a bit more.

Although I agree with Pat below (see my previous message) suppose I (or 
Richard) disagree(s) and want(s) to stick to the assertion
http://dbpedia.org/resource/Berlin owl:sameAs 

Does that mean that what I get from the two resources should be not only 
consistent RDF descriptions, but *identical descriptions* ? I guess so. 
It's clear that it's not the current case.
Both URI use http content negociation, and redirect (when dbpedia server 
is not 503, as it is right now :-( )  to different html pages and 
different RDF descriptions (e.g., latitude and longitude are in the 
geonames description, not in the dbpedia one) each maintained in its 
respective domain.

In the best of Semantic Web worlds, should not those two resources, if 
declared the same, yield indeed the *same* content trough http protocol 
(at least the same RDF content)? Which means either both URI actually 
redirect to the same one (one of them, or a third one) to ensure the 
description is unique, or the contents are somehow synchronised, which 
might be quite tricky to implement.

I would be happy to have Pat's and/or Tim's opinion on this:
Is such an implementation necessary and/or sufficient to say that 
owl:sameAs is not misused / abused?



Pat Hayes a écrit :
>> 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> .
> Ah, no. You can't do that so, er, confidently. After all, you are 
> punning, using the same URI to denote several things, so you should 
> only say they are equal in this strong sense when they are equal in 
> ALL their uses. And of course they aren't: they denote different web 
> pages.
>> 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?
> You overused owl:sameAs. Logical equality has to be used with care 
> when punning, its true. This is why OWL 1.1 will (at the time of 
> writing) have three distinct equalities, and why the CL semantics uses 
> true semantic overloading rather than punning, speaking strictly.
> BTW, I opposed including owl:sameAs, i.e. simple equality, into OWL 
> for exactly this reason. But I was overruled :-)
>> 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?
> See above. But just using a sanctioned vocabulary is no safeguard 
> against getting wrong conclusions. You MISused owl:sameAs here.
> Equality is very dangerous. If I have two ontologies, one which treats 
> human beings as agent continuants and refers to me using 
> <http://BOF/PatHayesEnduring/>, and the other which treats humans as a 
> subclass of SpatiotemporalThings and uses a process-based ontology, 
> and refers to me as <http://FourDrUs/PatHayesTheLife/> and someone 
> casually asserts
> <http://BOF/PatHayesThePerson/> owl:sameAs <http://FourDrUs/PatHayes/> .
> because they both denote the same person, you will get the same kind 
> of error. Its not enough to just denote the same person, in some loose 
> everyday sense of 'same': it has to denote precisely the same 
> *ontological entity*. Those things can be very exactly drawn, and have 
> all kinds of metaphysical superstructure attached to them by the 
> ontologies they happen to be used in. In the case of punning, it has 
> to be thought of as a kind of n-tuple of all the things the name can 
> be used to refer to. So your owl:sameAs was just false, sorry.
>>> 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.
> Hmmm. You may be right. Certainly it would be safer, if we could 
> manage it. But I don't think we can possibly manage it.
> But you have made a very nice case, which nobody has made to me 
> before. Thanks.
> Pat


*Bernard Vatant
*Knowledge Engineering
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Received on Thursday, 14 June 2007 10:56:38 UTC

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