[SKOS] Re: SKOS comment: Last Call Working Draft [ISSUE-181]

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 it correctly, your issue is that instances of 
skos:Collection cannot be included in hierarchies. Otherwise you could 
have represented your "centered entities" as collections.
As you noted, we clearly distinguish the two "groupings" and 
"semantic networks" notions [6], and your "centered entities" cannot be 
modelled as Collections.
Also, your "non-assignable concepts" heading hints that another solution 
would be possible, had we proposed a solution to the requirement 
R-IndexingAndNonIndexingConcepts [2]. Indeed, I guess your 
"non-assignable" concepts can be likened to what we called "non-indexing 
concepts". But R-IndexingAndNonIndexingConcepts has been dropped [4], as 
the indexing property requirement ISSUE-48 [3] (see note (1)).

As a consequence of these problems having beeing already being 
extensively discussed, we propose to *close* ISSUE-181 [ISSUE-181], 
making no change to the existing SKOS documents. *We hope that you are 
able to live with this.*

Please note however that it is still possible to coin a practice for 
representing centered entities as instances of skos:Concepts, provided 
you make your own (small) extension to SKOS [5]. The following steps 
should be taken, to obtain your own solution to 
- first, identify an indexing property you want to use to link concepts 
to other resources (e.g. dc:subject).
- second, define a subclass of skos:Concept, e.g. 
my:NonAssignableConcept, as not being usable together with your indexing 
property. This can be done in OWL using an appropriate cardinality 

I hope this helps. Note that whether you find the practice
suggested here appropriate, 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 an 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-181] http://www.w3.org/2006/07/SWD/track/issues/181
[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
[5] http://www.w3.org/TR/2008/WD-skos-primer-20080829/#secskosspecialization
[6] http://www.w3.org/2006/07/SWD/track/issues/33

(1) Note that this is 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.

Received on Thursday, 6 November 2008 14:00:36 UTC