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Re: Exactly what does broader/narrower mean?

From: Jakob Voss <jakob.voss@gbv.de>
Date: Mon, 19 Feb 2007 16:48:34 +0100
Message-ID: <45D9C6D2.70502@gbv.de>
To: public-esw-thes@w3.org
Cc: Sören Auer <auer@informatik.uni-leipzig.de>, Richard Cyganiak <richard@cyganiak.de>

Hi Richard, hi Sören,

Looks like the group of people dealing with this aspects of knowledge
organization is small so there are always the same people ;-)

You wrote:

> In Wikipedia, there are often category hierarchies like this:
>     Germany
>       |
>       +-- German politicians
> Can this be translated to SKOS? 
> If Germany and German politicians are skos:Concepts, then is there a
> skos:broader relationship between them?

Yes - the hierarchical relations between Wikipedia categories are an
application of SKOS.

> I'm a bit concerned that one isn't really a sub-topic of the other.
> To phrase the question differently: Is there a clear test to decide if A
> skos:broader B? For RDFS class hierarchies it's simple: A
> rdfs:subClassOf B iff all instances of A are also instances of B. What
> would be the equivalent rule for SKOS?

We don't have instances in SKOS but resources that are indexed with
concepts. The rule in SKOS may be:

A skos:narrower B if all resources that are indexed with A may also be
indexed with B.

The point is that "may also be indexed" is a much more vague constraint
than beeing an instance also - and it depends on the context of your
application. You may index all German politicians with "Germany" so
users will find them when searching for "Germany". But if there are too
many resources indexed with "Germany" than it's better to select a more
detailed concept - it just depends on! Alistair presented the semantic
model of cost expansion to deal with hierarchic relations in skos when
doing retrieval, but this is only one possible application.

Do you know Sorites paradox? Consider a heap of sand from which grains
are individually removed. If you remove a single grain of sand of it, it
still remains a heap - so you may conclude that a heap may be composed
by just one grain of sand! This is also the nature of skos:broader: its
a vague property. This may scare traditional AI fundamentalists, but it
allows practical usage with real world resources and people with real
world information needs.


For limited Cost Expansions see: Alistair Miles: Retrieval and the
Semantic Web, page 32ff

For more about Wikipedia category hierarchies see
Voss: Collaborative thesaurus tagging the Wikipedia way.

The chapter about hierarchical relations in a student paper I wrote in
2003 may also be of interest. Today I would not write it in the same way
but the basics still apply:
http://eprints.rclis.org/archive/00007589/, page 28.
Received on Monday, 19 February 2007 15:48:23 UTC

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