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Re: SKOS Extensions ... broaderDirect/narrowerDirect ... ?&In-Reply-To=<F5839D944C66C049BDB45F4C1E3D

From: Dan Brickley <danbri@w3.org>
Date: Fri, 26 Aug 2005 09:47:41 +0100
Message-ID: <430ED72D.1000000@w3.org>
To: Mark van Assem <mark@cs.vu.nl>
Cc: Antoine Isaac <Antoine.Isaac@kb.nl>, public-esw-thes@w3.org

Mark van Assem wrote:

>
>
> Hi Antoine, all,
>
> The question of distinguishing between immediate parents/children is 
> also present for rdfs:subClassOf. It requires some calculation but 
> it's possible to determine the direct relationships (see also the 
> directSubclassOf operator in SeRQL [1]) by determining that there 
> isn't an intermediate class Z between classes X and Y. So a "direct" 
> relationship is not indispensible I think.
>
> Of course it would be easier if the relationships were there 
> explicitly from the start. If people think that's better to have then 
> I would consider putting skos:directBroader/Narrower into the core and 
> recommend its usage instead of putting it in the extensions [2], as 
> you already say.
>
> I couldn't come up with a use case in which it is *crucial* to make 
> the distinction, but maybe some others on this list can?

I'm pretty wary of this notion of 'direct' versus implied, as it 
interacts awkwardly with the open-world assumptions behind Web (and 
Semantic Web) architecture...

eg.

class dan:Car
  subclass: mark:MotorCar
     subclass dan:ExpensiveMotorCar

In the 'dan' scheme, we might assert that dan:ExpensiveMotorCar
is a sub class of the class dan:Car. Elsewhere in the Web, someone else
(eg. you) might describe a class 'MotorCar' that fits between the two in the
hierarchy. Does this fact that someone has taken the time to document 
this new
intermediate class make the relationship between dan:Car and 
dan:ExpensiveMotorCar
any less direct? Perhaps only if the dan: schema is ammended to mention 
it? Even
within a single vocabulary, we run into similiar issues around 
versioning, addition of
new terms.

"Directness" is relative. I expect query tools and databases (eg. built 
on SPARQL) will
be used by applications who do care to know whether some relationship 
(eg. subClassOf)
is directly asserted, versus implied, within a particular dataset. But I 
really have my
doubts that this is usefully expressed in a de-contextualised way in 
terms of a 'directness'
relationship between terms. These comments are mostly w.r.t. the general 
RDF issues, but
I think they apply to directBroader too.

Dan
Received on Friday, 26 August 2005 08:47:38 GMT

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