# 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>

Hi,

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

A(_1).

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}

or

\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}

or

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

or isn't there any?

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

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 21:45:17 GMT