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[SKOS] Re: SKOS comment: Last Call Working Draft [ISSUE-183]

From: Antoine Isaac <aisaac@few.vu.nl>
Date: Tue, 04 Nov 2008 21:58:06 +0100
Message-ID: <4910B75E.9000603@few.vu.nl>
To: "Panzer,Michael" <panzerm@oclc.org>
CC: public-swd-wg@w3.org

Dear Michael,

Thank you for your comments [1]:

3. Class-Topic relationships

This issue seems to cause some general problems for using SKOS as a
general tool to model classification systems, since the fundamental
entity in a classification system is not the concept but the class, or,
more precisely, the distinction between classes and their subjects.
There are numerous examples of problems that arise by the difficulty of
expressing in SKOS the interplay between a class and the subjects that
form that class on the basis of at least one common characteristic.

The inability to model other than concept-concept relationships with
SKOS sometimes leads to inconsistencies as subjects/topics are
frequently in the domain or range of common classification

In the DDC, this can manifest itself in classes being connected by both
hierarchical and non-hierarchical relationships if modeled with current

<A> skos:narrower <B> .
<B> skos:related <A> .

This arises because what is expressed here isn't really a relationship
between classes, but between topics and classes:

<A> ddc:narrower <B> .
<Topic_in_B> ddc:related <A> .

This pattern can also lead to circular hierarchical relationships:

<A> ddc:narrower <Topic_in_B> .
<B> ddc:narrower <Topic_in_A> .

At the moment in SKOS, this has to be coded at class level:

<A> skos:narrower <B> .
<B> skos:narrower <A> .

which produces inconsistencies. A possible solution would be to
introduce/define ddc:related (or similar relationships) as a new element
without extending SKOS semantic relationships, even if this would mean
lowering the utility of classification systems in SKOS applications.

SKOS does not indeed offer by default an exact solution to your problem. 

Our concern with this issue is that its scope might be 
limited, considering the general context of KOS practice. We have not 
identified that kind of situation in our Use Cases and Requirements 
document [2], even for the (UDC) classification case we had [3].

Further, your problem is quite difficult to get. I assume that 
"subject/topics", even if they are different from classes, are still of 
conceptual nature -- they indeed play a structuring role in your KOS. 
They can therefore be modelled as instances of skos:Concept in their own 
Consequently, you could model all your semantic relations as standard 
SKOS relations, at the level of topic/subjects, or between classes and 
subjects/topics, without having to represent them at the class level. 
And thus avoid the cycles you mention.

In the light of the assumed relative rarity of your case and existence 
of a potential solution for it, we propose to *close* ISSUE-183 [ISSUE-183], 
making no change to the existing SKOS documents. *We hope that you are 
able to live with this.*

Please note that it is still possible to coin a more refined practice, 
using existing properties from SKOS.
Namely, you can have "classes-as-concepts" (corresponding to the "core" 
classification scheme) in one concept scheme and "subject-as-concepts" 
in another concept scheme.
Concepts from two different schemes can be linked by semantic relations 
such as skos:broader. That would allow to consider subjects as 
hierarchical specializations of classes, similarly to what is presented 
as "concept scheme extension" in the Primer [5].

I hope this helps. Note that whether you agree with the practice
suggested here or come with a better solution, we encourage you to 
publish a brief note or a third-party extension proposal, and inform the 
SKOS community via the mailing list. This is important for us, and we'd 
be happy to set up a "community best practices" wiki page to collect 
links to such statements.

Best regards,


[ISSUE-183] http://www.w3.org/2006/07/SWD/track/issues/183
[1] http://lists.w3.org/Archives/Public/public-swd-wg/2008Oct/0061.html
[2] http://www.w3.org/2006/07/SKOS/UCR.html
[3] http://www.w3.org/2006/07/SWD/wiki/EucUDC
[4] http://www.w3.org/TR/2008/WD-skos-primer-20080829/#secconcept
[5] http://www.w3.org/TR/2008/WD-skos-primer-20080829/#secextension
Received on Thursday, 6 November 2008 13:53:54 UTC

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