RE : Suggestion for SKOS FAQ

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