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Re: Semantics question (was Re: XSLT question)

From: Stasinos Konstantopoulos <konstant@iit.demokritos.gr>
Date: Wed, 23 Apr 2008 17:53:54 +0300
To: Phil Archer <parcher@icra.org>
Cc: Public POWDER <public-powderwg@w3.org>
Message-ID: <20080423145354.GE28276@iit.demokritos.gr>

On Wed Apr 23 15:07:29 2008 Phil Archer said:

> I'm sorry Stasinos, this must be frustrating for you, but let me try this.
>
> <owl:Restriction>
>   <owl:onProperty rdf:resource="&bbfc;rated" />
>   <owl:hasValue rdf:resource="&bbfc;_12" />
> </owl:Restriction>
>
> is OK iff
>
> <rdf:Description rdf:about="&bbfc;_12">
>   <bbfc:rated>12</bbfc:rated>
>   <bbfc:consumerAdvice>May contain nuts <bbfc:consumerAdvice>
> </rdf:Description>
>
> Because bbfc:rated appears in the restriction and in the filler, but if  
> we remove that bbfc:rated property from the rdf:Description, then it all  
> falls apart?

This is not OK because bbfc:rated is at the same time a data property
and an object property. This is OK:

<owl:Restriction>
  <owl:onProperty rdf:resource="&bbfc;rated" />
  <owl:hasValue rdf:resource="&bbfc;_12" />
</owl:Restriction>

<rdf:Description rdf:about="&bbfc;_12">
  <bbfc:rate>12</bbfc:rate>
  <bbfc:consumerAdvice>May contain nuts <bbfc:consumerAdvice>
</rdf:Description>

Where bbfc:rated is an object property linking our resource with the
bbfc:_12 instance, which in its own turn has two data properties, 
bbfc:rate and bbfc:consumerAdvice.

> My basic struggle here is that (as you know) we're trying to end up with  
> triples that have the candidate resource as their subject. Given
>
> <descriptorset>
>   <ex:property rdf:resource="&ex;foo" />
> </descriptorset>
>
> and a candidate URI of u, well, it's easy to see
>
> <rdf:Description rdf:about="u">
>   <ex:property rdf:resource="&ex;foo" />
> </rdf:Description>
>
> as the output.
> 
> Dan and Jeremy went to great lengths to explain some restrictions on  
> this when I saw them together in Bristol at the end of last year. This,  
> for example, would be unacceptable:
>
> <rdf:Description rdf:about="u">
>   <ex:property>
>     <ex:Class>
>       <ex:property2 rdf:resource="&ex;foo" />
>     </ex:Class>
>   </ex:property>
> </rdf:Description>
>
> ... it's the semantics of the blank node that mess this up - so we do  
> already have limits on the expressivity of a DR's descriptor element,  

Exactly, and this happens because you tried to make a class be the value
of a property, which you cannot.

> but being able to say
>
> <descriptorset>
>   <ex:property rdf:resource="&ex;foo" />
> </descriptorset>
>
> would be good to be able to do - even if we have to make clear the  
> limitations of what &ex;foo can be.

ex:foo must be the RDF node of an individual, of a single thing. As
opposed to the node of a class, a set of things.

s
Received on Wednesday, 23 April 2008 15:20:02 GMT

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