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Re: Why do you want to do that?

From: Pat Hayes <phayes@ihmc.us>
Date: Sun, 10 Aug 2008 20:36:35 -0700
Message-Id: <p06230916c4c5634dbdb0@[]>
To: "Richard H. McCullough" <rhm@pioneerca.com>
Cc: "Semantic Web at W3C" <semantic-web@w3.org>, "KR-language" <KR-language@YahooGroups.com>, "Adam Pease" <adampease@earthlink.net>
At 7:46 PM -0700 8/10/08, Richard H. McCullough wrote:
>1. You have caused me to re-evaluate my proof, and I now see
>that I skipped over an interesting step.  Let me start again.
>By the definition of
>     X  subClassOf  Y
>there are only two possibilities
>     X  properSubClassOf  Y
>     X  equivalentTo  Y
>Likewise, if
>     X  subClassOf  X
>then either
>     X  properSubClassOf  X
>     X  equivalentTo  X
>Since the former is false, the latter must be true.
>     X  sameAs  X
>must be either true or false.

No, it must be true. This really is just plain true, given the 
semantic conditions for sameAs.

>If it is true, that means that X is unambiguous, and
>the context of X includes one definition of X.

It has nothing to do with ambiguity or contexts. In any case, OWL/RDF 
does not deal with such matters.

>If it is false, that means that X is ambiguous, and
>the context of X includes two or more distinct
>definitions of X.
>2. Two distinct definitions of X
>     X  type  Y;
>     X  subClassOf  Z;
>are being merged into the same context. 

These aren't "distinct definitions". They aren't definitions in nay 
case, but these two assertions are simply consistent. Something can 
(in RDFS and CL and OWL-Full) be both a class and an individual. Put 
another way, a class can be an individual. There aren't two different 
things being merged, and there aren't any contexts.

>Generally speaking, I think it is better to keep
>the distinct definitions in separate contexts,
>and to be aware that you are switching contexts.

I agree, if any context switching were going on, but it there isn't.


>Dick McCullough
>Ayn Rand do speak od mKR done;
>mKE do enhance od Real Intelligence done;
>knowledge := man do identify od existent done;
>knowledge haspart proposition list;
>----- Original Message -----
>From: <mailto:phayes@ihmc.us>Pat Hayes
>To: <mailto:rhm@pioneerca.com>Richard H. McCullough
>Cc: <mailto:semantic-web@w3.org>Semantic Web at W3C ; 
><mailto:KR-language@YahooGroups.com>KR-language ; 
><mailto:adampease@earthlink.net>Adam Pease
>Sent: Friday, August 08, 2008 10:56 PM
>Subject: Re: Why do you want to do that?
>At 8:21 AM -0700 8/8/08, Richard H. McCullough wrote:
>>Over the last six years, I have suggested a number of
>>"improvements" to the RDF language.  Not one of
>>my suggestions was adopted.
>Working groups get many, many suggestions, and only a very small 
>fraction of them get adopted. Nothing personal.
>>  Apparently,
>>RDF is fine just the way is, thank you!
>>I would now like to turn the tables, and ask
>>why do you want to do that?
>>I'll start with two features of RDF which seem to be popular.
>>1. X  subClassOf  X;
>>A neat mathematical property, right?
>Im not sure why you call it 'mathematical'. It follows from the 
>usual definition of subClass, which is that A subClass B just when 
>every member of A is also a member of B. Given this, its obvious 
>that A is a subClass of A.
>>But if you do the inferences, what it means is
>>    X  sameAs  X;
>No, what it means is what it says, that A is a subclass of itself. 
>Being a subclass of, and being identical to, are not the same 
>For example, suppose you know, or can find out, that A subClass B 
>and also that B subClass A. Now you can infer that A and B are the 
>same class (more exactly, in RDFS, that they are equivalent, ie have 
>the same members.)
>>We already knew that.
>But the utility is precisely in the case where we did not know that, 
>but were able to infer it.
>>Why do you want to do that?
>>2. X  type  Y;  X  subClassOf  Z;
>>Another neat property: X is an individual and a class.
>Now I can ... What?  I don't know.
>I suspect you have not tried to use actual ontologies in practice. 
>There are so many things you can do that its hard to know where to 
>begin. For example, you can categorize properties (= classes)  into 
>types. We do this when we talk of a physical property, for example, 
>or a legal contract. Classifications often treat types of things as 
>individuals, as in a parts catalog (where a 'part' is listed with a 
>price per hundred, say.) The part has a part number and is treated 
>like an individual during the catalog search process but treated as 
>a classification when computing the actual order and pricing. When 
>merging information from multiple sources it is often essential to 
>be able to keep track of classes used by different sources, and this 
>is best encoded as a property of classes; so the classes are the 
>individuals of the property. This particular feature is so 
>universally used that leaving it out of OWL-DL meant that it was the 
>most requested 'extension' in OWL-2.
>>Why do you want to do that?
>>Dick McCullough
>>Ayn Rand do speak od mKR done;
>>mKE do enhance od Real Intelligence done;
>>knowledge := man do identify od existent done;
>>knowledge haspart proposition list;
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Received on Monday, 11 August 2008 03:37:38 UTC

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