Re: Question about problems with top/bottom property

Bijan, Alan,

thanks. I think I get it:-)

Ivan

Bijan Parsia wrote:
> 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.
> [snip]
> 
> 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:
>     http://www.w3.org/2007/OWL/wiki/Universal_Property
> 
> 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.
> 
> Cheers,
> Bijan.
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
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