[SKOS] A comment on Primer from Alasdair Gray (was RE : RE : Suggestion for SKOS FAQ)

Hi Alasdair,

I forward this comment [1] to the SWD working group list, as we want to keep track of all comments for the SKOS docs.
We'll try to address it asap.
If you have other comments please do not hesitate! Your input is *really* useful for our work.

Best,

Antoine

[1] http://lists.w3.org/Archives/Public/public-esw-thes/2008Mar/0019.html


-------- Message d'origine--------
De: Alasdair J G Gray [mailto:agray@dcs.gla.ac.uk]
Date: mar. 11/03/2008 10:46
À: Antoine Isaac
Cc: Simon Spero; al@jku.at; iperez@babel.ls.fi.upm.es; SKOS
Objet : Re: RE : Suggestion for SKOS FAQ
 
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
> À: 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/

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