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Uncles in OWL DL

From: Denny Vrandecic <dvr@aifb.uni-karlsruhe.de>
Date: Thu, 23 Aug 2007 12:01:59 +0200
Message-ID: <46CD5B17.5010203@aifb.uni-karlsruhe.de>
To: semantic-web@w3.org


I know I probably have a mistake in here, but I am not sure where it is. 
Maybe you can help me.

In OWL DL it is possible to say


with _1 being a blank node. It is also possible to say the semantically 
equivalent thing

{_1} ⊑ A

or, if you don't have Unicode:

{_1} \sqsubseteq A

which means that the nominal consisting of the blank node _1 is a 
subclass of the class A.

Now, since this is possible, why can't I say

∃father.{_1} ≡ ∀sibling.∀father.{_1}


\exists father.{_1} \equals \forall sibling. \forall father.{_1}

which supposedly means that if someone has a father, all his siblings 
also have to have the same father.

A colleague, Markus Krötzsch, tried to explain me that the problem lies 
with the interpretation of the blank node. But then I don't get the 
difference to

∃father.{a} ≡ ∀sibling.∀father.{a}


\exists father.{a} \equals \forall sibling. \forall father.{a}

or isn't there any?

A bit confused,
Received on Thursday, 23 August 2007 10:02:10 UTC

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