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Re: Why do you want to do that?

From: Richard H. McCullough <rhm@pioneerca.com>
Date: Sun, 10 Aug 2008 19:46:38 -0700
Message-ID: <2FAD7234C8AE476DA9C2DC837D8F0468@rhm8200>
To: "Pat Hayes" <phayes@ihmc.us>
Cc: "Semantic Web at W3C" <semantic-web@w3.org>, "KR-language" <KR-language@YahooGroups.com>, "Adam Pease" <adampease@earthlink.net>
Re: Why do you want to do that?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
or
    X  equivalentTo  Y

Likewise, if
    X  subClassOf  X
then either
    X  properSubClassOf  X
or 
    X  equivalentTo  X
Since the former is false, the latter must be true.

Now,
    X  sameAs  X
must be either true or false.

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

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

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;
http://mKRmKE.org/

  ----- Original Message ----- 
  From: Pat Hayes 
  To: Richard H. McCullough 
  Cc: Semantic Web at W3C ; KR-language ; 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 relationship.


  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.


  Pat


    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;
    http://mKRmKE.org/




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Received on Monday, 11 August 2008 02:50:44 GMT

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