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Re: Modelling 'term-to-term' relationships in SKOS

From: Leonard Will <L.Will@willpowerinfo.co.uk>
Date: Wed, 3 Mar 2004 18:20:50 +0000
Message-ID: <N1Y606UCIiRAFAgM@willpowerinfo.co.uk>
To: public-esw-thes@w3.org

In message 
<350DC7048372D31197F200902773DF4C047485F4@exchange11.rl.ac.uk> on Wed, 3 
Mar 2004, "Miles, AJ (Alistair)" <A.J.Miles@rl.ac.uk> wrote
>
>I designed SKOS to be strictly concept-oriented.  In this view there are
>only 'concepts' and 'labels'.
>
>Antonymy:
>
>In the concept-oriented view, 'antonymy' would be represented as a 
>relationship between two concepts.  So in an imaginary thesaurus, 
>concept A (label 'Black') is opposite of concept B (label 'White').  As 
>an extension of SKOS, the relationship 'is opposite of' would be 
>modelled as a sub-property of skos:SemanticRelation.

There are some cases where apparent antonyms are alternative labels for 
the same concept. "Dryness" and "wetness" for example are both possible 
labels for the concept of "moisture content". (The "half-full" or 
"half-empty" situation.)

>Equivalence between terms:
>
>In the concept-oriented view, a label is simply a string.  Therefore, there
>is no notion of 'equivalence' between labels.
>
>A label may be used as a label for more than one concept.

This worries me. A label is only of use if it identifies the thing it 
labels. I may have three jars labelled "coffee", of which one contains 
coffee, one contains tea and the other contains sugar, but this is not 
the sort of situation we should accept.

Did you mean to say that a concept may have more than one label? That is 
certainly true, and two labels that refer to the same concept could 
reasonably be said to be "equivalent".

>However, a label is always considered to be empty of meaning. 
>Therefore, there is no notion of 'equivalence' between a label and a 
>concept.

Perhaps not "equivalence" but still a close association. The label is a 
convenient way of referring to the concept, avoiding the need to write 
out the scope note in full every time you want to refer to it. If I 
label a jar "coffee", "café" or "641.3373", those symbols are by no 
means empty of meaning; they indicate the same substance even though the 
character strings are not "equivalent" to the substance.

>SKOS supports a notion of 'equivalence' between concepts.  This may 
>either be modelled as a sub-property of skos:SemanticRelation (i.e. an 
>intra-thesaurus relation) or a sub-property of skos-map:SemanticMapping 
>(i.e. an inter-thesaurus relation).
>
>E.g. SKOS-Mapping contains the property skos-map:exactMapping, which 
>could be used to express an 'exact equivalence' relationship between 
>two concepts.

>E.g. SKOS-Mapping contains two properties skos-map:MajorMapping and 
>skos-map:MinorMapping, which could be used to express greater or lesser 
>degrees of 'equivalence' between concepts.

As you have indicated, equivalence between concepts is something that 
should arise only when mapping between different thesauri.

If two concepts within a single thesaurus are exactly equivalent, I see 
no need for them both to be present. They should be combined, as there 
is only one concept, not two.

If there is partial equivalence between concepts in a single thesaurus, 
then either one is a narrower term of the other or else there is an area 
of overlap (e.g. "ships" and "boats"). In the latter case the scope of 
each concept should if possible be redefined so as to eliminate this 
overlap, as it will lead to uncertainty in using the thesaurus. An 
associative link may then be made between the two related concepts.

It must be difficult to differentiate between MajorMapping and 
MinorMapping, but it is probably helpful to have these to indicate large 
or small extents of overlap.
>
>Final word:
>
>This is how I think of it.  To switch from a 'term-oriented' view to a
>'concept-oriented' view, instead of 'term' think 'concept+label'.

Or 'concept + as many labels as necessary' (of which one may be 
designated as the "preferred" label or "descriptor").

>What does everyone think?
>
>Al.

My tuppence worth.

Leonard
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Received on Wednesday, 3 March 2004 13:21:27 GMT

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