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RE: asymmetric VS non-symmetric

From: Michael Schneider <schneid@fzi.de>
Date: Fri, 31 Jul 2009 19:42:23 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A0015DD8BF@judith.fzi.de>
To: "Antoine Zimmermann" <antoine.zimmermann@deri.org>
Cc: "W3C OWL Working Group" <public-owl-wg@w3.org>
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



>-----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.
>Antoine Zimmermann
>Post-doctoral researcher at:
>Digital Enterprise Research Institute
>National University of Ireland, Galway
>IDA Business Park
>Lower Dangan
>Galway, Ireland

Dipl.-Inform. Michael Schneider
Research Scientist, Dept. Information Process Engineering (IPE)
Tel  : +49-721-9654-726
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Email: michael.schneider@fzi.de
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Received on Friday, 31 July 2009 17:43:08 UTC

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