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Re: asymmetric VS non-symmetric

From: Antoine Zimmermann <antoine.zimmermann@deri.org>
Date: Fri, 31 Jul 2009 19:35:00 +0100
Message-ID: <4A733954.5070505@deri.org>
To: Michael Schneider <schneid@fzi.de>
CC: W3C OWL Working Group <public-owl-wg@w3.org>
Michael,

You are right, there is probably no interesting use case for the 
non-symmetric properties. I just didn't think about it when I was 
assuming non-symmetry.

I admit that "asymmetric relations" in logics is (apparently) 
exclusively defined as in OWL 2 (which is indeed the only definition 
that is really useful).

However, it is the case that "asymmetric", even in mathematics, is used 
as a place-holder for "not symmetric". You may, though, have to consider 
things out of the restricted case of set-theoretic relations (e.g., 
symmetric numbers, symmetric figures, etc.) For non-mathematicians, my 
experience is that people use "asymmetry/asymmetric" in common language 
for denoting non-symmetry/not symmetric (regardless of the domain it is 
applied to).

My suggestion is simply to evacuate a potential false assumption by 
concisely stating that [asymmetry != non-symmetry]. IMO, it would be 
enough to update Primer and NF&R only, because people who look at the 
formal specs are probably more maths/logic-minded and would not be 
surprised by the definition.

Regards,
AZ.

Michael Schneider wrote:
> Hi Antoine!
> 
> First, let me say that in logics/mathematics literature I have never seen
> any other use of "asymmetric" than the way we are using it in our documents
> (the "hard" form). 
> 
> More, I would not easily see any use case for having non-symmetry as a
> modeling feature. It would tell me something like that for any model of the
> ontology there would exist some property assertion for which there is no
> corresponding reverse property assertion; but not knowing which property
> assertion is meant, and it can be a different one for different models. What
> does this information buy me?
> 
> (But if you really like to have non-symmetry as a feature, you can still
> have it under the RDF-based semantics by stating something like
> 
>     ex:p rdf:type [ owl:complementOf( owl:SymmetricProperty ) ] . 
> 
> This is, of course, not possible in OWL 2 DL.
> )
> 
> But I agree that adding some informative note should be ok, and can even put
> it in the CRs, IMO.
> 
> For the RDF-Based Semantics, I think what is already in for some months
> should be sufficient:
> 
> [[
> If two individuals are related by a symmetric property, then this property
> also relates them reversely, while this is never the case for an asymmetric
> property. 
> ]]
> 
> Agreed?
> 
> Cheers,
> Michael
> 
>> -----Original Message-----
>> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org]
>> On Behalf Of Antoine Zimmermann
>> Sent: Friday, July 31, 2009 1:21 PM
>> To: 'W3C OWL Working Group'
>> Subject: asymmetric VS non-symmetric
>>
>> Dear all,
>>
>> Until today, I did not look at the semantics of AsymmetricProperty
>> because the word was familiar enough to me to intuitively understand it.
>> I was however wrongly assuming that the word was used to denote
>> non-symmetric. From a linguistic perspective, asymmetry is a lack or
>> absence of symmetry. Some mathematical texts use "asymmetric" to simply
>> mean "not symmetric".
>>
>> I am aware that "asymmetric relation" is often used in mathematics to
>> denote "strongly asymmetric relation", i.e., no pairs of elements are
>> related in a bidirectional (symmetric) way. While it is perfectly ok
>> that OWL2 defines AsymmetricProperties the way it does, I am surprised
>> not to find *any* remark, neither in the formal specs, nor in the UFDs,
>> nor in the mailing list archives, about the fact that AsymmetricProperty
>> is not the complement of SymmetricProperty.
>>
>> I am sure that other people are understanding asymmetry in the same way
>> as I did, so I'd suggest adding a small sentence in the Primer (Sect.6.1
>> [1]) and NF&R (Sect.2.2.3 [2]) stating that "asymmetric" is not the
>> negation of "symmetric". Since the UFDs are still in LC, this should be
>> addressed somehow.
>>
>> [1]
>> http://www.w3.org/TR/2009/WD-owl2-primer-
>> 20090421/#Property_Characteristics
>> [2]
>> http://www.w3.org/TR/2009/WD-owl2-new-features-
>> 20090421/#F6:_Reflexive.2C_Irreflexive.2C_and_Asymmetric_Object_Properti
>> es
>>
>> Regards,
>> --
>> Antoine Zimmermann
>> Post-doctoral researcher at:
>> Digital Enterprise Research Institute
>> National University of Ireland, Galway
>> IDA Business Park
>> Lower Dangan
>> Galway, Ireland
>> antoine.zimmermann@deri.org
>> http://vmgal34.deri.ie/~antzim/
> 
> --
> Dipl.-Inform. Michael Schneider
> Research Scientist, Dept. Information Process Engineering (IPE)
> Tel  : +49-721-9654-726
> Fax  : +49-721-9654-727
> Email: michael.schneider@fzi.de
> WWW  : http://www.fzi.de/michael.schneider
> =======================================================================
> FZI Forschungszentrum Informatik an der Universität Karlsruhe
> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
> Tel.: +49-721-9654-0, Fax: +49-721-9654-959
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> Vorstand: Prof. Dr.-Ing. Rüdiger Dillmann, Dipl. Wi.-Ing. Michael Flor,
> Prof. Dr. Dr. h.c. Wolffried Stucky, Prof. Dr. Rudi Studer
> Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
> =======================================================================


-- 
Antoine Zimmermann
Post-doctoral researcher at:
Digital Enterprise Research Institute
National University of Ireland, Galway
IDA Business Park
Lower Dangan
Galway, Ireland
antoine.zimmermann@deri.org
http://vmgal34.deri.ie/~antzim/
Received on Friday, 31 July 2009 18:36:15 GMT

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