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Re: asymmetric VS non-symmetric

From: Pascal Hitzler <hitzler@aifb.uni-karlsruhe.de>
Date: Tue, 04 Aug 2009 14:15:48 +0200
Message-ID: <4A782674.5000301@aifb.uni-karlsruhe.de>
To: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
CC: Antoine Zimmermann <antoine.zimmermann@deri.org>, Michael Schneider <schneid@fzi.de>, W3C OWL Working Group <public-owl-wg@w3.org>
Yes and I've added this to the primer.

http://www.w3.org/2007/OWL/wiki/index.php?title=Primer&diff=25059&oldid=25056

Pascal.

Ian Horrocks wrote:
> 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/
>>
> 
> 
> 

-- 
PD Dr. Pascal Hitzler
pascal@pascal-hitzler.de   http://www.pascal-hitzler.de
Semantic Web Textbook: http://www.semantic-web-book.org
Received on Tuesday, 4 August 2009 12:13:06 GMT

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