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Re: Question about problems with top/bottom property

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Mon, 2 Jun 2008 13:46:53 +0100
Message-Id: <2395DDA5-2259-4843-BACE-4D39103C3792@cs.man.ac.uk>
Cc: Alan Ruttenberg <alanruttenberg@gmail.com>, Boris Motik <boris.motik@comlab.ox.ac.uk>, 'Michael Schneider' <schneid@fzi.de>, public-owl-wg@w3.org
To: Ivan Herman <ivan@w3.org>

On 2 Jun 2008, at 13:16, Ivan Herman wrote:

> Alan Ruttenberg wrote:
>> Is there any reason not to include bottom role? There is a  
>> debugging benefit to computing equivalentProperty to bottom role.
> I must admit I do not understand what you mean here.
> In general, I would like to understand the clear benefit the top  
> and bottom role would bring to OWL users. At the moment, it is  
> unclear to me.

We have had extensive discussion on this, so perhaps as summary is due.

 From a UI perspective, Top and Bottom properties add symmetry (i.e.,  
analogues to Thing and Nothing) and thus a more uniform UI. For  
example, right now, it is rare (unknown?) for reasoners to report  
unsatisfiable properties (which do occur). A natural way to report  
this is to show them as equivalent to or subsumed by a Bottom  
property (in analogy with how unsatisfiable classes are handled).

Similarly, I find users adding an artifical top property (or asking  
for one) just to help organize their properties. (I find this a bit  
odd, personally, but that's what it is.)

 From an expressiveness point of view see:

In general, TopProp (my new favored name :)) allows one to express co- 
existence constraints *without* specing a particular relation between  
the two entities. For example, you might wish to express that if  
there is a disease occurrence then there is a cause (germ, poison,  
trauma, genetic defect) without necessarily having a "local top"  
causal property (i.e., a generic caused by):

	DiseaseOccurrence sub (someValuesFrom owl:universal owl:Thing)

(or some more specific class of causal agents).

	DiseaseAfterTraumaOccurrence sub (someValuesFrom owl:universal Trauma)

(Where the way the trauma causes the disease might be unspecified or  
one of a number of disjoint mechanism).

In this case, you can capture the structure by other means (including  
simulating the TopProp). But it does seem more direct and flexible.

Received on Monday, 2 June 2008 12:44:47 UTC

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