AW: [Welcoming feedback] Semantic Web: Information wants to be useful

Hi Pat,
 
>PS. What does Cyc do about elements which only exist macroscopically as
compounds? If there are no pieces of pure Ytterium, say, then the class
Ytterium is the empty class. If there are no pure samples of
Einsteinium, similarly. In an OWL reasoner, you could infer that they
are the same class, hence sameAs one another (since they are both
classes). 
 
I feel like we should be more careful about the term "the same class".
Two classes are not the same only because they are both empty - centaurs
and unicorns are not the same. 
 
"NOTE: The use of owl:equivalentClass does not imply class equality.
Class equality means that the classes have the same intensional meaning
(denote the same concept). " [1]
 
Best,
Heiko.
 
[1] http://www.w3.org/TR/owl-ref/#equivalentClass-def

________________________________

Von: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org] Im
Auftrag von Pat Hayes
Gesendet: Dienstag, 12. Mai 2009 16:48
An: David Baxter
Cc: semantic-web@w3.org
Betreff: Re: [Welcoming feedback] Semantic Web: Information wants to be
useful



On May 12, 2009, at 9:06 AM, David Baxter wrote:


	Pat Hayes said:
	
	> I know both Cyc and dbPedia say their
	> concepts are sameAs one another, but they are both wrong. Cyc
defines
	> a 'piece' of carbon; dbpedia defines the chemical element
carbon.
	> These concepts are NOT owl:sameAs one another, no matter what
the
	> websites say.
	
	
	Hi Pat,
	
	We're definitely interested in improving the quality of our
owl:sameAs links to DBpedia and other datasets. In this case, however, I
believe the owl:sameAs link is good -- it's the OpenCyc comment that's
bad. The URI opencyc:Carbon
<http://sw.opencyc.org/concept/Mx4rvVjIQpwpEbGdrcN5Y29ycA>  denotes an
owl:Class representing the element carbon. Its instances are individual
pieces of carbon, including diamonds and lumps of coal. We'll get the
comment fixed.
	


Hmm. So - just to see if I follow you here - Cyc thinks that a chemical
element *is* the class of all its macroscopic pieces? Is this what
DBpedia also thinks a chemical element is? Because (a) that seems to me
to be a very idiosyncratic view of what a chemical element is, and (b)
if DBpedia has some other ontology of chemical-element-hood, then your
two concepts are very unlikely to the sameAs one another. Bear in mind
that owl:sameAs really does mean logically identity, so ANYTHING said
using one name is true using the other. So someone should be able to
take any DBpedia content mentioning carbon, and any piece of Cyc content
mentioning carbon, substitute one carbon name for the other throughout
both chunks, and conjoin them, and the result ought to make sense in
both systems. Is that indeed true, in this case? 

Pat

PS. What does Cyc do about elements which only exist macroscopically as
compounds? If there are no pieces of pure Ytterium, say, then the class
Ytterium is the empty class. If there are no pure samples of
Einsteinium, similarly. In an OWL reasoner, you could infer that they
are the same class, hence sameAs one another (since they are both
classes). 



	David Baxter
	Cycorp
	


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