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Re: Equality of RDF bags

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Fri, 28 Oct 2011 23:12:37 +0200
Cc: Dieter Fensel <dieter.fensel@sti2.at>, Antoine Zimmermann <antoine.zimmermann@emse.fr>, Heiko Paulheim <paulheim@ke.tu-darmstadt.de>, semantic-web@w3.org
Message-Id: <31FB2FCA-A343-48DA-B505-9BF82F3AE02D@inf.unibz.it>
To: Martin Hepp <martin.hepp@ebusiness-unibw.org>
Indeed.
From the RDF semantics you can not infer from equal partial descriptions of anonymous objects that the objects are equal.
A simpler example: if "a" is a person having 49 years old, and b is a person having 49 years old, then I can *not* infer that a is equal to b; this would be definitely non intuitive.
Your intuition is not matched by the RDF semantics in the original example since you are "illegally" overloading the meaning of the properties as representing "elements" of a "set" denoted by the anonymous object. But nothing says that here we are talking about real sets and their real elements.
--e.

On 28 Oct 2011, at 20:24, Martin Hepp wrote:

> Hi Dieter, all:
> Note that two blank nodes having the same attributes and the same type may still represent two distinct entities with a different identity. In particular if you think of changing RDF data (SPARUL updates, this can be an important distinction.
> 
> For instance, if in GoodRelations, two items momentarily have the same price, e.g.
> 
> foo:offer1 a gr:Offering;
>    gr:name "ACME Laptop" ;
>    gr:hasPriceSpecification [ 
>        a gr:UnitPriceSpecification;
>    	gr:hasCurrency "USD"^^xsd:string;
>    	gr:hasCurrencyValue "9.90"^^xsd:float;
>    	gr:hasUnitOfMeasurement "C62"^^xsd:string ] .
> 
> foo:offer2 a gr:Offering;
>    gr:name "ACME Semantic Web Services Book" ;
>    gr:hasPriceSpecification [ 
>        a gr:UnitPriceSpecification;
>    	gr:hasCurrency "USD"^^xsd:string;
>    	gr:hasCurrencyValue "9.90"^^xsd:float;
>    	gr:hasUnitOfMeasurement "C62"^^xsd:string ] .
> 
> Then you should not infer that both have the same entity representing the unit price, because these may evolve differently, so you should not infer that they have the same price, but just that their anonymous price node has currently the exact same attributes. But sameness in type and attributes does not say anything about whether this is the same entity, as long as the descriptions of each node are incomplete, which is always the case.
> 
> I may not oversee all aspects of the RDF formal semantics in this, but at least from a GR perspective the first intuition is wrong.
> 
> Martin
> 
> 
> 
> On Oct 28, 2011, at 4:42 PM, Dieter Fensel wrote:
> 
>> At 11:19 AM 10/28/2011, Antoine Zimmermann wrote:
>>> Graph 2a and Graph 2b are not equivalent either in terms of formal semantics,
>> 
>> Is it then fair to say that the formal RDF semantics is "broken" not reflecting the intuitive semantics of RDF?
>> 
>> 
>> -- 
>> Dieter Fensel
>> Director STI Innsbruck, University of Innsbruck, Austria
>> http://www.sti-innsbruck.at/
>> phone: +43-512-507-6488/5, fax: +43-512-507-9872
>> 
>> 
> 
> 
Received on Friday, 28 October 2011 21:13:11 GMT

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