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Re: RE : Suggestion for SKOS FAQ

From: Andreas Langegger <al@jku.at>
Date: Tue, 11 Mar 2008 12:14:01 +0100
Cc: Antoine Isaac <Antoine.Isaac@KB.nl>, Simon Spero <ses@unc.edu>, iperez@babel.ls.fi.upm.es, SKOS <public-esw-thes@w3.org>
Message-Id: <28E92BD6-348E-4909-A1DC-9EC2B0050223@jku.at>
To: Alasdair J G Gray <agray@dcs.gla.ac.uk>

first I din't pay much attention to your discussion, because I thought  
this case is clear... looking at the spec I read  
"skos:broaderTransitive owl:subClassOf skos:broader" - but there it  
says (to my surprise): skos:broaderTransitive and others are "super  
properties" - why that?

If I would model this I would say:

skos:semanticRelation a owl:ObjectProperty .
skos:broader a skos:semanticRelation .
skos:narrower a skos:semanticRelation .
skos:broaderTransitive a skos:broader; a owl:TransitiveProperty .
skos:narrowerTrasnsitive a skos:narrower; a owl:TransitiveProperty .
and so on...

can anybody comment on this why the specs says "super property" and  
not "sub property" ?
Whith the statements above I can deceide whether to allow transitivity  
or not. And because of OWA, skos:broader not explicitly asserted as a  
transtive property, it does not mean, that it _cannot be_ transitive,  
sure it can, but it does not need to be valid.

If a taxonomy should be ISO2788 compliant, just use the *Transitive  
versions - so it's up to the modeler and not to the application which  
I think is fine.


On Mar 11, 2008, at 10:46 AM, Alasdair J G Gray wrote:

> Hi Antoine,
> I've got to admit that in reading the SKOS Primer [2], in particular  
> sections 2.3.1 and 4.7, I became very confused as to the properties  
> of skos:broader and skos:broaderTransitive. In particular the fact  
> that skos:broaderTransitive is a super property of skos:broader.
> However, reading your mail below has cleared things up for me.  
> Perhaps the primer should be more explicit in the difference.
> Cheers,
> Alasdair
> [2] http://www.w3.org/TR/skos-primer/
> Antoine Isaac wrote:
>> Hi Simon,
>> Two objections to your mail:
>> 1. I still don't get it why ISO2788 says BT *should* be transitive.  
>> Of course there can be interpretations that leads to this, but it's  
>> still not 100% clear to me. Can you quote a sentence that makes you  
>> say so?
>> 2. In the exemple you give, SKOS does not prohibit A broader C. We  
>> say that broader is *not transitive*, that different from saying  
>> that it is *intransitive* (or "antitrantisitive") ! "transitivity  
>> does not hold" does *not* mean that (NOT A broader C) is valid in  
>> all cases.
>> Maybe actually point 2 is an answer to point 1, if you got our  
>> proposal for skos:broader semantics wrong.
>> To sum up:
>> - from A skos:broader B, B skos:broader C you cannot automatically  
>> infer A skos:broader C: there are concept schemes for which this  
>> would be assuming too much coherence for the hierarchical links.
>> - there can be concept schemes for which the co-existence A  
>> skos:broader B, B skos:broader C and A skos:broader C is OK. Maybe  
>> all thesauri that are compliant with ISO2788, if ISO2788 say BT is  
>> always transitive. But the A skos:broader C was in that case  
>> produced by some knowledge that is not in the SKOS semantics.
>> Does it make the situation clearer? You can also go to [1], when  
>> Alistair noticed this subtle differences (that had been also  
>> interfering with the SWD working group discussions)
>> Best,
>> Antoine
>> [1] http://lists.w3.org/Archives/Public/public-esw-thes/2007Dec/0052.html
>> -------- Message d'origine--------
>> De: public-esw-thes-request@w3.org de la part de Simon Spero
>> Date: ven. 07/03/2008 23:58
>> └: al@jku.at
>> Cc: iperez@babel.ls.fi.upm.es; SKOS
>> Objet : Re: Suggestion for SKOS FAQ
>> On Fri, Mar 7, 2008 at 4:54 PM, Andreas Langegger <al@jku.at> wrote:
>> >
>> >  thanks for the pointer to issue-44. I didn't read deep into the  
>> thread.
>> > But as Antoine pointed out, there is the transitive version also  
>> (obviously
>> > the result of the issue-44 discussion). So both kinds of  
>> semantics can be
>> > expressed in the model and are not defined by the application.
>> >
>> The problem with the introduction of an intransitive "broader"  
>> relationship
>> is that such a relationship is fundamentally incompatible with the  
>> Broader
>> Term relationship as defined in ISO-2788 et. al.
>> The defining characteristic of hierarchical relationships  is that  
>> they are
>> totally inclusive.  This property absolutely requires  
>> transitivity.  If this
>> condition does not apply, the relationship is associative, not  
>> hierarchical.
>>   Renaming the broader and narrower term relationships doesn't  
>> change this;
>> all it has done is cause confusion.
>> As an example of the confusion so caused, note that associative
>> relationships remain disjoint from broaderTransitive (S24)?    If  
>> "broader"
>> can be intransitive, this constraint is inexplicable.
>> Let A,B,C be Concepts,
>>        A broader B,
>>        B broader C,
>> and suppose that transitivity does not hold (  NOT A broader C)
>> By S18,  we have
>>       A broaderTransitive B,
>>       B broaderTransitive C,
>> By S21,
>>       A broaderTransitive C
>> and hence, by S24,
>>       NOT A related B,
>>       NOT B related C,
>>       NOT A related C
>> We have NOT A broader C and NOT A related C, so there can't be any
>> relationship between A and C  at all!
>> Simon
> -- 
> Dr Alasdair J G Gray
> http://www.dcs.gla.ac.uk/~agray/
> Explicator project
> http://explicator.dcs.gla.ac.uk/
> Office: F161
> Tel: 	+44 141 330 6292
> Postal: Computing Science,
> 	17 Lilybank Gardens,
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> 	Glasgow,
> 	G12 8QQ, UK.

Dipl.-Ing.(FH) Andreas Langegger
Institute for Applied Knowledge Processing
Johannes Kepler University Linz
A-4040 Linz, Altenberger Stra▀e 69
Received on Tuesday, 11 March 2008 11:14:29 UTC

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