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Re: N3 contexts vs RDF reification

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 1 May 2001 19:09:27 -0500
Message-Id: <v04210109b714c91c5f68@[205.160.76.204]>
To: "Seth Russell" <seth@robustai.net>
Cc: www-rdf-interest@w3.org
>Well, sorry,  I'm still not getting this.  Could I impose on you again to
>refer to a new mentograph:
>
>[1] http://robustai.net/mentography/TransitiveProperties.gif
>
>See  you say ...
>
>    "What you are talking about is meta-language statements
>    (statements about other statements),
>    not higher-order statements."
>
>Yet I have been able to transform the two examples of  "higher-order
>statements" that you gave below into RDF statements merely about other
>statements - which I take to mean that statements can be objects of other
>statements.

Have you? "Transform" in what sense? How do you know it preserves 
meanings?  I don't know what the semantics of your diagrams is, so I 
don't know how to evaluate what it is that they are supposed to say. 
What is the meaning of "method", for example? Where does your 
notation distinguish quantifiers over objects from quantifiers over 
relations? Or show the scope of a quantifier? (BTW, even being 
charitable, I think the first diagram has several bad problems. You 
only have one quantifier, and you put it below the scope of the 
implication, and you seem to have the antecedent and consequent of 
the implication conjoined together. )

Just drawing a pointer from one node to another doesn't say anything 
by itself. You have to specify the meaning of the pointer. For 
example, I notice that you have nodes labelled 'implies' (a logical 
connective) and also labelled with variable names and also with what 
look like relation names. All these are different syntactic 
categories in logic, and play different roles in giving meanings, so 
I don't think that your diagrams can possibly mean what they would 
need to mean in order to say what they seem to want to say.

>So I am at a loss to make the distinction you require.

Well, the distinction is what it is, independent of any diagrams 
anyone might draw. There is clearly a distinction between relations 
and sentences, for example.

>A couple of notes on my diagram.
>
>* I use a short-hand notation for RDF reification - explained at
>[2] http://robustai.net/mentography/reification.gif

I have to admit that I am still not exactly sure what reification 
means in the RDF context. If it means the same there as elsewhere, 
then any use of propositional connectives (like and , or , not , 
implies) together with reification is almost certainly not going to 
make sense. For example, the meaning of '(not P)' is not the same as 
the meaning of 'not' applied to the sentence 'P' (it is applied to 
the *meaning* of the sentence 'P', not to the sentence itself.) RDF 
usage of reification seems mix up the idea of a subexpression with 
the idea of a metalangauge reference.

>* I had to change your example slightly away from unary relations so as to
>correspond with the RDF way of doing things.  But I was able to duplicate
>the problem to which you referred and then resolve it with a arc labeled
>"not" between the variable class and the designated class.

On what basis do you claim that inserting an arc (with ANY label) is 
a resolution of the problem? To show that you will need to provide a 
semantics for your arc notation and show that the meaning of the 
larger graph is the intended meaning.

>So, what am I missing ??

Im not sure, but I think the answer is, a grasp of what semantics is about.

Pat Hayes

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Received on Tuesday, 1 May 2001 20:09:41 GMT

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