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Re: TR : [SKOS]: [ISSUE 44] BroaderNarrowerSemantics

From: Leonard Will <L.Will@willpowerinfo.co.uk>
Date: Mon, 14 Jan 2008 21:46:47 +0000
Message-ID: <uapZTGPHh9iHFAzy@mail.willpowerinfo.co.uk>
To: SWD WG <public-swd-wg@w3.org>, SKOS <public-esw-thes@w3.org>

On Mon, 14 Jan 2008 at 18:15:23, Antoine Isaac <aisaac@few.vu.nl> wrote
>I'd like to have your opinion on the example I will adapt from in [1], itself
>adapted from Simon's previous mails

>Consider we have a thesaurus that says:

>> mountains regions BT Himalaya
>> Himalaya BT Everest


Antoine -

Just to clarify this example first, I should note that the normal
convention in thesaurus circles, and in BS8723-2, para.8.3.1, is to
interpret BT as meaning "has the broader term" and NT as "has the
narrower term".  ISO 2788, paragraph 4.1, also reads

        BT Broader term; the term that follows the symbol represents a
        concept having a wider meaning

I remember some previous discussion on the SKOS list about the ambiguity
of using these abbreviations the other way round, to mean "is the
broader term of", for example. This can easily give rise to confusion
and should be sorted out urgently. Thus I would write your example above
as

mountainous regions
NT Himalaya

Himalaya
NT Everest

where the first is in fact an NTI relationship (i.e., for Margherita's
benefit, narrower term instantive, meaning that the proper name Himalaya
is a specific instance of a mountainous region, the reciprocal
relationship being BTI). The second is a NTP relationship (i.e. narrower
term partitive, meaning that Everest is a part of the Himalaya,
reciprocal BTP).

>If BT is transitive, than for the query "give me the concepts that linked tio
>montains regions via BT" we'll get "Himalaya" and "Everest". To me (and
>others), this raise the following issues:

>- "mountains regions" BT "Everest" may seem questionable (especially if
>we know this KOS to be carefully designed, following e.g. ISO2788!)

>- both concepts are now given as if siblings, losing track of the initial
>design.
>
>In the end I feel that the second is the most serious one, since if we go for a
>very rough specification of broader (fitting classification schemes' idea of
>hierarchy for instance) we could still argue that indeed there is a form a
>'broader' statement between the two concepts. But anyway, I'd like to have
>your opinion on both ;-)

I think the issue is how transitivity is to be used. The main use of a
hierarchy, apart from displaying structure and giving logical paths for
navigation, is to allow a search for a concept to be expanded to include
narrower concepts. In the generic case this is valid because the
narrower concepts are specific classes which fall within the broader
concept. The rules for indexing are generally that you allocate the most
specific terms possible to a document, and you can rely on the thesaurus
to enable these concepts to be found even when the search is expressed
in broader terms.

The whole/part or "partitive" relationship can lead to problems, and
BS8723-2, paragraph 8.3.3.1 says that it should normally be restricted
to four specific cases:

a) systems and organs of the body
b) geographical locations
c) disciplines or fields of discourse
d) hierarchical social structures.

The "Himalaya NTP Everest" example falls into case b), and it is
reasonable that someone searching for information about the Himalaya and
any of its parts should wish to retrieve items that have been indexed
with the term "Everest".

I agree that if transitivity is to work across mixed types of
relationship, we would have to interpret NT to mean "has the more
specific concept, part or instance", to generalise what Simon Spero
suggested. If you then had

EU countries
NTI France

France
NTP Paris

it would be true to say that Paris is a more specific concept, part or
instance of an EU country. Perhaps we should adopt this meaning.

We should note, though, that this type of interpretation is used when
deciding how to expand a search using a thesaurus hierarchy. It does not
allow you to modify the hierarchy itself, by designating France and
Paris as siblings. BS8723-2, paragraph 14.3 g), specifically forbids
this, saying

        Validation checks should prevent the entry of inadmissible
        relationship combinations. If two terms already have one of the
        standard relationships, no other standard relationship between
        the same terms is admissible. If term A has BT term B, none of
        the terms in the BT hierarchy above term B should be admissible
        as BT, NT or RT of term A.

This means that we cannot create a direct relationship which jumps over
the middle concept. It seems to me that we have two options:

1. If the consequence of this is that transitivity is in general not
valid, then SKOS should reflect that;

2. If we accept the generalised definition of hierarchical relationship,
e.g. using NT to mean "has the more specific concept, part or instance",
then we can assume transitivity.

I don't know which of these fits best with the purpose and approach of
SKOS. I think the decision should come from an examination of use cases.

Leonard
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Received on Monday, 14 January 2008 21:52:48 GMT

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