[sc34wg3] New SAM PSIs

[Murray Altheim]

Rath, Holger (empolis KL) wrote:
> Murray Altheim [mailto:m.altheim@open.ac.uk] wrote:
> 
>>Lars Marius Garshol wrote:
>>
>>>* Murray Altheim
>>>| 
>>>| First, I don't understand what a "subtype loop" is logically,
>>>| and I can't quite think what it could be, in FOL terms. Steve?
>>>
>>>A subtype loop looks as follows in LTM syntax:
>>>
>>>  super-sub(a : superclass, b : subclass)
>>>  super-sub(b : superclass, a : subclass)
>>>
>>>(Assuming, of course, that 'super-sub', 'superclass', and 'subclass'
>>>have been assigned the correct PSIs.)
>>
>>Okay, so this is something that is syntactically possible but
>>logically impossible. I'm not sure why it's proposed, unless
>>there's some domain when something's superclass can also be a
>>subclass of it. I can't think of any examples.
>
> DAML+OIL defines the equality between classes that way.

Regardless of what DAML+OIL does, what does it *mean*? I'm
confused. It's nonsense, AFAIK:

      A is superclass of subclass B
      B is superclass of subclass A

That doesn't make logical sense. (I must be missing something
here, as defining equality of two classes based on them being
both superclasses and subclasses of each other seems to ignore
the very definitions of superclass and subclass.)

Murray

......................................................................
Murray Altheim                  <http://kmi.open.ac.uk/people/murray/>
Knowledge Media Institute
The Open University, Milton Keynes, Bucks, MK7 6AA, UK

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