W3C home > Mailing lists > Public > public-owl-wg@w3.org > August 2009

Re: asymmetric VS non-symmetric

From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
Date: Mon, 3 Aug 2009 15:40:12 +0100
Message-Id: <580D305A-C35E-457D-BBD2-EC8450A33CC7@comlab.ox.ac.uk>
Cc: Michael Schneider <schneid@fzi.de>, W3C OWL Working Group <public-owl-wg@w3.org>
To: Antoine Zimmermann <antoine.zimmermann@deri.org>
I think that we are in vehement agreement here. A very small addition  
to Primer and NF&R pointing out that asymmetric is much stronger than  
simply not symmetric (and vice versa) seems harmless and might even  
eliminate a source of possible confusion.

Ian



On 31 Jul 2009, at 19:35, Antoine Zimmermann wrote:

> 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
>> Stiftung des bürgerlichen Rechts, Az 14-0563.1, RP Karlsruhe
>> 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 Monday, 3 August 2009 14:40:53 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 3 August 2009 14:40:53 GMT