Re : Re: characteristics of properties

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Re : Re: characteristics of properties

Nivu Niconnu
Hello Martin,

I know the difference in the defintion.
What I don't understand is why the GUI of Protégé proposes a switch (Functional or not) or a choice (Symmetric, Asymmetric or none of the 2).
You can specify that a property is Symmetric, is Asymmetric or is none of the 2 (neither Symmetric, nor Asymmetric).
Whereas you can't do the same for a Functional property: either it is or it is not. It could be 'unknown' (open world hypothesis)
Is my point clearer ?


Best Regards.

 

----- Message d'origine -----

De : Martin Kuba

Envoyés : 30.05.11 10:19

À : User support for the Protege-OWL editor

Objet : Re: [protege-owl] characteristics of properties


 
Hi Nivu, 

the difference between functional and symmetric is that functional means 'has at most one value' 
while symmetric means 'if it points in one direction, it points also in the opposite direction', 
see 

http://www.w3.org/TR/owl2-direct-semantics/#Object_Property_Expression_Axioms 

for exact definitions and see 

http://www.w3.org/TR/owl2-syntax/#Functional_Object_Properties 
http://www.w3.org/TR/owl2-syntax/#Symmetric_Object_Properties 

for examples. The a:hasFather property is functional but not symmetric, 
while the a:friend is symmetric but not functional. 

Best regards 

Martin 

Dne 30.5.2011 10:04, Nivu Niconnu napsal(a): 
> Hello all, 
> 
> a question related to the *default status *regarding *properties*. 
> 
> In *Protégé GUI* (4.1.0, Build 213), a *data property* can be functional. If nothing is explicitely mentioned it is supposed to be *not* functional, it does not make any difference in the GUI. 
> For *object properties*, it is different: a property can be functional, inverse functional, transitive. By default it is not. And also an object property can be symmetric *or* asymmetric, reflexive 
> *or* irrreflexive. 
> What I understand from this is that *by default *an object property that is not said symmetric is not asymmetric either (same thing for reflexive). 
> 
> In the *open world* hypothesis, it would seem logical to think that if a status is not explicitely declared we can't assume whether it is true or false. It should be 'unknwon' unless explicitely declared. 
> 
> So why is there a difference between functional and symmetric? 


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CERIT-SC                               Martin Kuba 
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Re: Re : Re: characteristics of properties

Thomas Russ

On May 30, 2011, at 4:24 AM, Nivu Niconnu wrote:

> Hello Martin,
>
> I know the difference in the defintion.
> What I don't understand is why the GUI of Protégé proposes a switch  
> (Functional or not) or a choice (Symmetric, Asymmetric or none of  
> the 2).
> You can specify that a property is Symmetric, is Asymmetric or is  
> none of the 2 (neither Symmetric, nor Asymmetric).
> Whereas you can't do the same for a Functional property: either it  
> is or it is not. It could be 'unknown' (open world hypothesis)
> Is my point clearer ?

Because Functional and not Functional are opposites.

Symmetric and Asymmetric are separate characteristics that are not  
opposites.

If a property is not symmetric, it does not mean that it is  
asymmetric, so each of those is a separate property.
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