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ISSUE-185 new draft response

From: Antoine Isaac <aisaac@few.vu.nl>
Date: Wed, 22 Oct 2008 11:42:23 +0200
Message-ID: <48FEF57F.60106@few.vu.nl>
To: SWD WG <public-swd-wg@w3.org>

Hi all,

Here's a new draft response to Michael on [ISSUE-185]. Please let me 
know what you think, especialy wrt. formality level!


Dear Michael,

Thank you for your comments [1]:
5. Order in Classification Systems

Order in a classification is important, indeed critical. Order is
evident in the juxtaposition of classes, the sequence of main classes,
and the sequence of co-ordinates in a class. Broader and narrower
relationships alone cannot represent order. So, maybe parallel encoding
is necessary to make sure that the system a classification scheme tries
to present is reflected when using SKOS.

To some degree, when order is connected to hierarchy, this can be
reflected by extensions to SKOS. The DDC for example has two parallel
hierarchies, one expressed by length of notation, the other by structure
(notes, etc.). This is handled at the moment by extending skos:narrower.

skosclass:narrowerStructural rdfs:subPropertyOf skos:narrower .

skosclass:broaderStructural rdfs:subPropertyOf skos:broader ;
 owl:inverseOf skosclass:narrowerStructural .

As a matter of fact, SKOS does not offer by default a solution that 
would fit exactly your problem. Usual RDF statements are order-neutral, 
there is no other solution than using RDF lists for representing ordered 
groups. The problem is so inherent to RDF itself that I believe it would 
be counter-productive for us to propose a solution for this at the level 
of property representation (something like "the first subclass of this 
class is X").

Another reason is that this use case was not clearly identified 
beforehand in the SKOS Use Case and Requirements [2]. We can relate that 
to the SKOS mission as stated in the Introduction of the SKOS Primer: 
"The aim of SKOS is not to replace original conceptual vocabularies in 
their initial context of use, but to allow them to be ported to a shared 
space, based on a simplified model, enabling wider re-use and better 
interoperability." I think we're here in a case where standardization 
concerns dictate our not offering a specific solution.

Consequently, we propose to *close* ISSUE-185 [ISSUE-185], making no 
change to the existing SKOS documents. We hope that you are able to live 
with this.

Note however that it is actually possible to coin a practice that (maybe 
somewhat indirectly) addresses your specific problem. Namely using a 
second layer of SKOS collections to represent the order of the classes 
in the class specialization hierarchy, as the following example:

ex:class rdf:type skos:Concept .
ex:subclass1 rdf:type skos:Concept ; skos:broader ex:class .
ex:subclass2 rdf:type skos:Concept ; skos:broader ex:class .
_:b0 rdf:type skos:OrderedCollection;
   skos:prefLabel "ordered subclasses of class1"@en; # this label is 
optional of course!
   skos:memberList _:b1.
_:b1 rdf:first ex:subclass1 ;
   rdf:rest _:b2.
_:b2 rdf:first ex:subclass2 ;
   rdf:rest rdf:nil.

Of course we cannot ensure that this would be adopted for all other 
classifications represented in SKOS. But this fits exactly how 
Collections should be used in current SKOS. As collections cannot be 
included in the semantic relationship hierarchy, they have to be used 
"in parallel" to semantic links between concepts. Note that even though 
the solution is relatively complex, it might be not more complex than 
the parallel hierarchies you're hinting at, in fact.

In fact, if you believe however that this solution is inappriopriate, or 
that it should be mentioned in some document because the issue is more 
common that what we think, we encourage you to publish a brief best 
practice note and inform the SKOS community via the mailing list. We'd 
be more than happy to set up a "SKOS community best practices" wiki page 
to collect links to such statements! Generally elements that you have 
brought in [1] could be a useful addition to the practices presented in 

Best regards,


[ISSUE-185] http://www.w3.org/2006/07/SWD/track/issues/185
[1] http://lists.w3.org/Archives/Public/public-swd-wg/2008Oct/0061.html
[2] http://www.w3.org/TR/SKOS-UCR
[3] http://esw.w3.org/topic/SkosDev/ClassificationPubGuide?rev=12
Received on Wednesday, 22 October 2008 09:42:51 UTC

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