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ISSUE-181 draft response

From: Antoine Isaac <aisaac@few.vu.nl>
Date: Thu, 16 Oct 2008 14:41:50 +0200
Message-ID: <48F7368E.9010500@few.vu.nl>
To: SWD WG <public-swd-wg@w3.org>

Hi all,

Here's a draft response to Michael on [ISSUE-181], let me know what you 
think. Note *this is just a draft, not the actual response* -- I'll wait 
for feedback from the WG before replying formally to
to Michael. (Michael: if you're lurking on this list feel free to post 
your thoughts at any time.)

Antoine

Dear Michael,

Thank you for your comments [1]:

1. Non-assignable concepts
--------------------------
Classification systems usually contain objects that are, while not being
assignable concepts, nonetheless an integral part of the system (not
just a display/presentation device), e.g., number spans or - in case of
the DDC - so-called "centered entries":

T2-486-T2-488 Divisions of Sweden
333.7-333.9 Natural resources and energy 

A centered entry represents a subject covered by a span of numbers.
Centered entries relate notationally coordinate classes together as a
single concept. For example, T2-485 represents Sweden; the centered
entry T2-486-T2-488 represents the geographic divisions of Sweden.
Centered entries are an important part of the structural hierarchy,
representing true broader concepts, even though this superordination is
not indicated by notation. In addition, as they often contain
instructions applicable to all subordinate classes, centered entries
cannot be modeled as a skos:Collection, since skos:Collection cannot be
part of the concept hierarchy (as defined in 9.6.4). A new class or
expanded skos:Collection class is required to allow concept collections
like spans or centered entries to be expressed as concepts.

-------------------------------------------------------------------

If I understand your case correctly, your issue is caused by the 
constraint that states that instances of skos:Collection cannot be 
included in concept hierarchies. Otherwise you would just have been able 
to represent your "centered entities" as instances of this class.

But as you noted, we made the choice to clearly distinguish the 
definition of "groupings" from the one of "semantic networks", and your 
"centered entities" cannot be modelled as Collections.
The only reasonable choice in the "standard"SKOS model is thus to 
represent centered entities as instance of plain skos:Concepts.

We could have proposed a more appropriate solution to you, if we had 
accepted the requirement R-IndexingAndNonIndexingConcepts [2] and 
proposed a solution to it. Indeed, I guess your "non-assignable" 
concepts can be likened to what we called "non-indexing concepts". But 
as the requirement of having an indexing property in SKOS has been 
dropped in ISSUE-48 [3], we have dropped 
R-IndexingAndNonIndexingConcepts as well [4].

Therefore, given the current SKOS model, what I would recommend as a 
solution to your specific case is to make your own solution to 
R-IndexingAndNonIndexingConcepts. That is:
- first, identify an indexing property you want to use to assign 
concepts to other resources (e.g. dc:subject).
- second, define a subclass of skos:Concept, e.g. 
my:NonAssignableConcept, which is defined as not being usable as the 
object of statements involving the chosen indexing property. This can be 
done in OWL, using a property inverse of the indexing property and an 
appropriate OWL cardinality constraint.

That being said, we would like not to make any changes in the current 
documents about recommanding such an approach. Not because the 
requirement you express is very rare, but because we would rather remain 
agnostic with respect to how SKOS entities are used (or not) in specific 
indexing situations, e.g. what property is used to index. This is one of 
the reasons why we did not include our own indexing property in the SKOS 
model!

I hope this helps and that you are able to live with the current  situation.

Best regards,

Antoine

[1] http://lists.w3.org/Archives/Public/public-swd-wg/2008Oct/0061.html
[2] http://www.w3.org/TR/SKOS-UCR#R-IndexingAndNonIndexingConcepts
[3] http://www.w3.org/2006/07/SWD/track/issues/48
[4] http://www.w3.org/2006/07/SWD/track/issues/46


> ISSUE-181: Last Call Comment: Non Assignable Concepts
>
> http://www.w3.org/2006/07/SWD/track/issues/181
>
> Raised by: Sean Bechhofer
> On product: SKOS
>
> Raised by Michael Panzer [1]:
>
>
> 1. Non-assignable concepts
> --------------------------
>
> Classification systems usually contain objects that are, while not being
> assignable concepts, nonetheless an integral part of the system (not
> just a display/presentation device), e.g., number spans or - in case of
> the DDC - so-called "centered entries":
>
> T2-486-T2-488 Divisions of Sweden
> 333.7-333.9 Natural resources and energy  
>
> A centered entry represents a subject covered by a span of numbers.
> Centered entries relate notationally coordinate classes together as a
> single concept. For example, T2-485 represents Sweden; the centered
> entry T2-486-T2-488 represents the geographic divisions of Sweden.
> Centered entries are an important part of the structural hierarchy,
> representing true broader concepts, even though this superordination is
> not indicated by notation. In addition, as they often contain
> instructions applicable to all subordinate classes, centered entries
> cannot be modeled as a skos:Collection, since skos:Collection cannot be
> part of the concept hierarchy (as defined in 9.6.4). A new class or
> expanded skos:Collection class is required to allow concept collections
> like spans or centered entries to be expressed as concepts.
>
>
> [1] http://lists.w3.org/Archives/Public/public-swd-wg/2008Oct/0061.html
>
>
>
>
>
>
>   
Received on Thursday, 16 October 2008 12:42:19 GMT

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