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Re: [protege-owl] Re: Protege-OWL Tutorial

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Fri, 25 Jun 2004 16:26:33 +0100
Message-ID: <40DC4429.2090609@cs.man.ac.uk>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: rhoadsnyc@mac.com, www-rdf-logic@w3.org

Peter F. Patel-Schneider wrote:
> Here are some quick comments on your questions.
> 

[snip]


>>4.  OWL Source Code
>>
>>In a future version of the tutorial [if you are so inclined to create one
>>;-)] it would be very helpful if you could display and explain the OWL code
>>resulting from operations in the GUI.
>>
>>I, for one, am often confused by the underlying code.  For example, I don't
>>understand why it is always necessary to relate a "Named" class to its
>>restrictions/axioms via "subClassOf" or "equivalentClass".  I suspect that
>>it has something to do with an Algebraic or logical equation.  (And maybe
>>it's time for me to go back and re-learn that stuff from High School).
>>
>>Take the SpicinessValuePartition, for example.  The resultant OWL code
>>looks like this (edited):
>>
>><owl:Class rdf:ID="SpicinessValuePartition">
>>   <owl:equivalentClass>
>>      <owl:Class>
>>         <owl:unionOf rdf:parseType="Collection">
>>            <owl:Class rdf:about="#Mild"/>
>>            <owl:Class rdf:about="#Medium"/>
>>            <owl:Class rdf:about="#Hot"/>
>>         </owl:unionOf>
>>      </owl:Class>
>>   </owl:equivalentClass>
>></owl:Class>
>>
>>Why is the following not sufficient?
>>
>><owl:Class rdf:ID="SpicinessValuePartition">
>>   <owl:unionOf rdf:parseType="Collection">
>>      <owl:Class rdf:about="#Mild"/>
>>      <owl:Class rdf:about="#Medium"/>
>>      <owl:Class rdf:about="#Hot"/>
>>   </owl:unionOf>
>></owl:Class>
> 
> 
> These two appear to me to be logically equivalent.  

subclass and equivalentClass axioms correspond to logical implication 
and bi-implication respectively. These are sometimes referred to as 
necessary conditions (an instance of the class necessarily satisfies the 
specified constraints) and necessary and sufficient conditions (an 
instance of the class necessarily satisfies the specified constraints, 
and satisfying the constraints is a sufficient condition for membership 
of the class).

In OWL (DL and Full) these such axioms can be asserted between arbitrary 
class descriptions. The first of the above forms allows for a consistent 
  structure for all four forms, i.e., whether the l.h.s. of the axiom is 
atomic or complex and whether the axiom is subClass or equivalentClass. 
The second form above only works for equivalentClass, and the 
equivalence is only implicit. A consistent and explicit structure is 
probably a good idea for humans, and I imagine that it also allows for 
more economical syntax generation code :-)

Ian



> 
> [...]
> 
> peter
> 
> 
Received on Friday, 25 June 2004 11:26:19 GMT

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