[foaf-dev] Group vs Class

Damian Steer pldms at mac.com
Fri Jun 11 23:31:02 CEST 2010

On 11 Jun 2010, at 20:42, Dan Brickley wrote:

> On Fri, Jun 11, 2010 at 6:07 PM, Ian Davis <me at iandavis.com> wrote:

>>> I mentioned this to Dave Reynolds recently, and he mentioned that the
>>> main problem is around identity conditions; in OWL (or DL flavours at
>>> least?) classes are identical by membership.
>> Identical or equivalent?
> Identical. But my memory is fading. I think final verdict was that the
> OWL flavours went one way, RDFS went the other.

The answer is 'equivalent' as in 'equivalentClass'.

OWL DL is effectively blind to the distinction between equivalence and equality: you can substitute one empty class for another without altering the meaning. OWL Full isn't like that:

"NOTE: The use of owl:equivalentClass does not imply class equality. Class equality means that the classes have the same intensional meaning (denote the same concept). In the example above, the concept of "President of the US" is related to, but not equal to the concept of the principal resident of a certain estate. Real class equality can only be expressed with the owl:sameAs construct. As this requires treating classes as individuals, class equality can only be expressed in OWL Full." [1]


[1] <http://www.w3.org/TR/owl-ref/#equivalentClass-def>

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