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Re: Why do you want to do that?

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 8 Aug 2008 22:56:34 -0700
Message-Id: <p06230914c4c2de62187b@[]>
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 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 Sunday, 10 August 2008 23:54:52 UTC

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