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Re: refining closure text for rdfs-isDefinedBy-semantics

From: patrick hayes <phayes@ai.uwf.edu>
Date: Mon, 10 Jun 2002 15:01:22 -0400
Message-Id: <p05111a00b929850feef7@[]>
To: Dan Brickley <danbri@w3.org>
Cc: w3c-rdfcore-wg@w3.org

>On Fri, 24 May 2002, Dan Brickley wrote:


>We can note that:
>RDF provides a property rdfs:isDefinedBy that is a specialisation of the
>rdfs:seeAlso property. This property is used to relate an RDF vocabulary
>term (such a Class or Property) to the context within which it
>is defined.

Not unless we first say what 'is defined' means. Right now it seems 
to me that it doesn't mean anything, which is why the MT doesn't 
assign it any meaning. (Maybe it really does mean something, but we 
ought to make an effort to say what it is. )

BTW, is rdfs:isDefinedBy really required to be a subproperty of 
rdfs:seeAlso?? If so, I should put that in the RDFS closure rules. I 
have absolutely no idea what this subproperty assertion is supposed 
to be saying, so I cannot tell whether it is supposed to be true.

>For every RDF property there is exactly one correct value for the
>rdfs:isDefinedBy property.

BUt that isnt expressible in RDFS. That is, two different urirefs 
might denote the same value, so 'unique value' doesn't cash out as 
'unique URI'. Do you want it to be possible to infer from

ex:foo rdfs:isDefinedBy ex:aaa .
ex:foo rdfs:isDefinedBy ex:bbb .

that ex:aaa and ex:bbb are equal? That would be a very creative way 
of introducing equality into RDF.

>When RDF graphs are written in the RDF/XML 1.0 syntax, this value
>corresponds to the XML namespace URIref used in the serialized
>representation of the RDF properties.
>can we take this as a basis for progress?

Not without a much clearer exposition of what it is talking about.

>The main clarification is that we represent explicitly the M+S claim that
>there is just one schema for each property,

But what does THAT mean? What is a 'schema' here? (People use this 
term a lot, but I have never seen it defined anywhere.) Do you mean 
there is at most one RDFS document that counts as the definition? If 
so, suppose the same term is used in another RDFS document, and I 
merge them. How does the part of the content that comes from the 
"definition" differ in meaning from the part that comes from 
somewhere else? If one graph contains a defined-by assertion, and the 
other graph uses that term, does the defined-by get incorporated into 
the merged graph? Does it then apply to the uses of the term that 
come from the document that DIDNT say refer to the definition? What 
happens if the two graphs being merged asserted different defined-bys?

>and that rdfs:isDefinedBy
>can thus be used to represent (within the RDF graph) the relationship that
>holds between a property and the namespace within which it is defined.

Again, I have no idea what this can mean. There is no notion of 
'definition' in RDF, seems to me: its a purely assertional language. 
And are you identifying 'schema' with 'namespace'?


>>	 - isDefinedBy is a Property
>>	 - it has no further semantics in the RDF Model Theory
>>	 - further sub-properties of it may be created by others
>>	 - RDF Core doesn't currently expect to create any of these.

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Received on Monday, 10 June 2002 15:01:27 UTC

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