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Re: Issue-114

From: Rinke Hoekstra <hoekstra@uva.nl>
Date: Tue, 1 Jul 2008 09:53:54 +0200
Cc: OWL Working Group WG <public-owl-wg@w3.org>
Message-Id: <283F26B8-02AE-47E9-9054-388CAD3CDCC1@uva.nl>
To: Alan Ruttenberg <alanruttenberg@gmail.com>

Hi,

On 30 jun 2008, at 22:26, Alan Ruttenberg wrote:
> There is no problem with individual/property punning - this is  
> included as valid in my proposal.

Whoops yes, sorry.

>> 2) A well known case is the relational nature of several roles,  
>> such as 'father'. Sometimes 'father' is used in the sense of  
>> 'has_father', sometimes it should be the class of fathers (or, more  
>> precisely, the role played by persons who are fathers). Again,  
>> using role inclusion axioms you can do a reification-like trick to  
>> infer the 'father' relation between two classes, given the chain  
>> has_father o played_by -> father.
>
> Could you write out what you mean by this in (possibly pseudo) OWL  
> and explain how I should understand it. I can't really understand  
> what you mean here.

Sure. It's not entirely fleshed out yet...

In LKIF Core we make a distinction between roles (anti-rigid) such as  
student, father and persons (similar to Searle's distinction between  
intrinsic and observer-relative/social facts). A person is said to  
'play' or 'count as' a role. (sure, whether the father-role is anti- 
rigid is debatable, but just assume for simplicity's sake). This is at  
odds with the common use of properties to denote roles, and frequently  
results in odd constructions. For instance,

Father subClassOf Person
Person equiv has_father exactly 1 Father

The class 'Father' cannot really be defined without the 'has_father'  
property: a rather circular definition, where the class and property  
have a similar status.

What we therefore try to do, is make the implicit role 'father'  
explicit as the reification of a 'father' property. In fact the  
'has_father' property in my original example, can be regarded as  
relating the context in which the father role is played to the role  
itself (I'll rename the has_father property from my original example  
to context_of, for sake of clarity).

If we now have the following classes:

father subClassOf (Role and played_by exactly 1 Person)
Person equiv context_of exactly 1 father

and the role inclusion axiom

context_of o played_by -> father

users of the ontology can choose to be either be explicit about  
context and roles, with the advantage of expressiveness, or just reuse  
the more implicit father property in more elaborate class  
restrictions. This improves reusability by information hiding. Of  
course, this only works in one direction: explicit constructions allow  
us to infer the implicit relation, but not vice versa.

-Rinke

-----------------------------------------------
Drs. Rinke Hoekstra

Email: hoekstra@uva.nl    Skype:  rinkehoekstra
Phone: +31-20-5253499     Fax:   +31-20-5253495
Web:   http://www.leibnizcenter.org/users/rinke

Leibniz Center for Law,          Faculty of Law
University of Amsterdam,            PO Box 1030
1000 BA  Amsterdam,             The Netherlands
-----------------------------------------------
Received on Tuesday, 1 July 2008 07:54:30 UTC

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