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Re: Semantic content negotiation (was Re: expectations of vocabulary)

From: Henry Story <henry.story@bblfish.net>
Date: Wed, 26 Jul 2006 17:19:42 +0200
Message-Id: <988A7C0F-8280-4221-B0F4-5E6034ADD21B@bblfish.net>
Cc: "'Reto Bachmann-Gmür'" <reto@gmuer.ch>, w3c semweb hcls <public-semweb-lifesci@w3.org>, "'Semantic Web'" <semantic-web@w3.org>
To: Chimezie Ogbuji <ogbujic@bio.ri.ccf.org>

On 26 Jul 2006, at 16:43, Chimezie Ogbuji wrote:
> On Wed, 26 Jul 2006, Henry Story wrote:
>
>>> I am still not sure if I understand you.  What is the  
>>> relationship between
>>> :CategoryList and :McDonaldCategoryList?  Are they under the same  
>>> namespace?
>>> If so, how are they related to each other?  And why would someone  
>>> build two
>>> set of vocabularies to describe the same thing?
>>
>> Good questions. My fault in not being careful with the example. I  
>> intended them to be
>> under different namespaces. So the examples should be
>>
>> <> a :CategoryList;
>>   :category [ :scheme <http://eg.com/cats/>;
>>               :term "dog" ];
>>   :category [ :scheme <http://eg.com/cats/>;
>>               :term "house" ].
>>
>> but I receive this
>>
>> <> a mcdo:CategoryList;
>>   mcdo:category [ mcdo:scheme <http://eg.com/cats/>;
>>               mcdo:term "dog" ];
>>   mcdo:category [ mcdo:scheme <http://eg.com/cats/>;
>>               mcdo:term "house" ].
>>
>>
>> I was just looking to see if there was a way to specify the  
>> content of rdf documents, because otherwise the flexibility of rdf  
>> could also be its doom.
>
> I don't follow how this is so, especially if there is no ambiguity  
> in the interpretation of either scenario (since owl:sameAs makes it  
> *crystal* clear that they are equivalent terms).

owl:sameAs means they refer to the same thing.

[[
The built-in OWL property owl:sameAs links an individual to an  
individual. Such an owl:sameAs statement indicates that two URI  
references actually refer to the same thing: the individuals have the  
same "identity".
]] http://www.w3.org/TR/owl-ref/#sameAs-def

So we have two terms that refer to the same thing, but this does not  
mean that a random agent knows that they do. The random agent may  
furthermore be quite limited as to its inferencing capabilities and  
so it may be very important for it to get the information in a  
vocabulary it can immediately understand.


>> If there were no way to expect that I would receive the first  
>> document rather than the second, since they both make the same  
>> statements about the world, then there would be no way to tell if  
>> I could ever seriously follow rdf links over the web.
>
> I still don't understand the motivation (or value) in micromanaging  
> which vocabulary terms are used when the interpretations are  
> unambigious (thanks in large part to ontology terms that were  
> designed precisely with this sort of thing in mind).

Well in non rdf schemas such as atom, it looks like every xml format  
needs its own mime type [1]. So when an agent GETs such a document,  
it will automatically know how to parse it, and how to interpret it.  
The problem there is that they end up with a huge mime type explosion  
problem [1].

In RDF on the other hand we can describe everything in the universe  
and beyond, using a handful of semantically equivalent mime types, of  
which "application/rdf+xml" is the best known. But now the mime type  
of a document gives us a lot less information about what can be found  
in the document, since so much more can be placed in the document.

The example I put forward and reproduced above show two semantically  
identical contents being returned, with the same mime type, but only  
one of them being interpretable immediately by my dumb client. This  
is the situation I was hoping to get a handle on.

>
>> But given that it is not impossible, if schemerama2 [1] type  
>> proposals can be formalised, then it looks like one can specify  
>> documents, not just by their format, but also by their content.   
>> This can then solve the problem I put forward above: since a  
>> document that contained the sentence "<> a mcdo:CategoryList ."  
>> but not the sentence "<> a :CategoryList ." would just simply be  
>> lying, even though
>>
>> mcdo:CategoryList owl:sameAs :CategoryList .
>
> Now I'm really confused.  So who is the final arbiter of validity:  
> the owl:sameAs statements expressed by the author of the vocabulary  
> or the consumer who demands that only a specific set of vocabulary  
> terms be used. It seems counter intuitive to expect to *both* rely  
> on vocabulary terms to express unambigious relationships between  
> terms and their interpretations as well as a transport mechanism to  
> control which terms you want used in response to a request.

You are confusing semantics with modes of presentation. Both  
documents above have been constructed in such a way that they  
describe exactly the same reality in the world.  But they present  
this differently. This is the famous "Hesperus is Phosphorus" example  
of Frege. Clearly the sentence "Superman is Superman" does not convey  
the same information as the sentence "Superman is Clark Kent" though  
semantically they refer to the same thing.

What some types of clients require is for reality to be presented to  
them using a certain vocabulary.

In so far as the two documents above use different vocabularies, they  
can be said to be different documents.


>
>> As such if I find a link on the web saying that some resource is  
>> a :CategoryList, I would be in my right to expect certain types of  
>> vocabularies to be used there.
>
> That pretty much renders the authority of terms such as owl:sameAs,  
> owl:equivalentClass, etc.. useless.

Nope see above the difference between semantics and meaning.

> Chimezie Ogbuji


Thanks for helping me make my points a little clearer,


Henry Story

Home page: http://bblfish.net/
Sun Blog: http://blogs.sun.com/bblfish/



[1] "no new mime types": http://www.imc.org/atom-protocol/mail- 
archive/msg05897.html
    This thread on Atom Application Protocol describes the mime type  
explosion problem that a normal xml format experiences. Some claim  
they need an extra mime type to describe a collection of things they  
already had. If every collection of things requires a new mime type,  
then the explosion is absolutely out of hand.
Received on Wednesday, 26 July 2006 15:20:03 GMT

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