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Re: ISSUE 77 and postcoordination [and ISSUE-40!]

From: Jakob Voss <jakob.voss@gbv.de>
Date: Mon, 10 Mar 2008 14:38:02 +0100
Message-ID: <47D539BA.9060501@gbv.de>
Cc: public-esw-thes@w3.org, public-swd-wg@w3.org

Hi Antoine,

ISSUE 40 is related but seems to go further. Some people distinguish 
"postcombination" and "postcoordination":

postcombinations:
* holiday, 2008
* 2008, holiday

postcoordinations:
* holiday IN 2008
* holiday BEFORE 2008

I think the second (postcoordination) is too complex, but 
postcombination should be supported. Mapping to combinations of concepts 
is just one application but more important is to encode subject indexing 
with multiple concepts. The order of concepts may be relevant and you 
surely want to encode additional metadata to subject indexing (who 
assigned it? when was it assigned?). One solution is reification but 
this is just terrible.

In Social tagging a common model is the triple model with resource <R>, 
tag <T>, and author <A>. There should be an easy way to encode such an 
indexing triple in SKOS. Thinking about this I found that Semantic 
Tagging (tagging with concepts instead of labels) could be encoded with 
skos:Collection. If person <P> tags resource <R> with concept <C>, this 
could be:


<R> skos:subject [
   rdfs:type skos:Collection ;
   dc:creator <P> ;
   skos:member <C>
] .

As said in the last mail this shoul entail

<R> skos:subject <C> .


Antoine wrote:

 > I find the pattern quite meaningful, but am really not sure that
 > using Collections is optimal.

Yes, using skos:Collection could be confusing - one alternative is to 
create another class like "skos:Combination" - but then you have to 
redefine skos:member. I find skos:Collection handy.

Greetings,
Jakob

> -------- Message d'origine--------
> De: public-esw-thes-request@w3.org de la part de Jakob Voss
> Date: lun. 10/03/2008 04:22
> └: public-esw-thes@w3.org
> Objet : ISSUE 77 and postcoordination
> 
> 
> Hi!
> 
> I must raise another issue related to ISSUE 77 (skos:subject) about
> collections of concepts. How do you encode postcoordination? After
> dealing with the encoding of classifications and authority files in SKOS
> I am working on a paper on encoding social tagging information with
> SKOS. So I stumbled upon the skos:subject property and encoding of
> subject indexing.
> 
> I was somehow suprised to see skos:subject missing in the current
> working draft (chapter 11.2, issue 77). To my point of view skos:subject
> is one of the pillars of SKOS (together with skos:Concept,
> skow:prefLabel and skos:broader/narrower). It might be enough to use
> dc:subject but then the SKOS recommendation should clearly state the
> semantics it implies with using dc:subject.
> 
> In particular I found two related gaps in the current draft. First is
> how to encode postcoordination of concepts and second is how to map to
> coordinated concepts. Let me give an example:
> 
> Given one Concept Scheme with two concepts labeled "holdiay" and "2008":
> 
>  x:holiday a skos:Concept; skos:prefLabel "Holiday" .
>  x:y2k8 a skos:Concept; skos:prefLabel "2008" .
> 
> How do you encode that fact that a resource '#R' was indexed with both
> together in a specific context (person, date, etc.)? You somehow have to
> connect two statements:
> 
>  #R skos:subject x:holiday .
>  #R skos:subject x:y2k8 .
> 
> Reification might be a solution but reification in RDF is where the real
> problems start, so better avoid it. The second use case is how to map a
> concept in one vocabulary to a union of two terms in another vocabulary.
> The early mapping spec [1] contained the classed AND, OR, and NOT but
> these seem to have faded away (?). OR is not a problem as far as I can
> see and NOT could be dropped because of complexity, but how do you
> encode an AND? Given a second Concept Scheme with a concept labeled
> "holiday2008":
> 
>  x:h2008 a skos:Concept; skos:prefLabel "2008" .
> 
> how do you encode the mapping between x:h2008 and x:holiday together
> with x:y2k8 ?
> 
> The solution I found, seems to answer both questions. First you have to
> broaden the rdfs:range of skos:subject, skos:exactMatch,
> skos:broadMatch, skos:narrowMatch and skos:relatedMatch from
> skos:Concept to skos:Concept, skos:Collection and
> skos:OrderedCollection. Second specify the semantics:
> 
> <A> skos:subject <C> .
> <C> a skos:Collection ; skos:member <X> , <Y> .
> 
> entails
> 
> <A> skos:subject <X> ; skos:subject <Y>
> 
> And the same with mapping relations instead of skos:subject and with
> skos:OrderedCollection instead of skos:Collection.
> 
> What does this mean? You can now
> 
> 1. Map between a concept and and a set of coordinated concepts:
> 
> x:y2k8 skos:exactMatch [
>   a skos:Collection;
>   skos:member x:holiday ;
>   skos:member x:y2k8
> ]
> 
> 2. Coordinate Concepts into a (sorted) collection and index resources
> with this coordinated collection.
> 
> #R skos:subject [
>   a skos:Collection;
>   skos:member x:holiday ;
>   skos:member x:y2k8
> ]
> 
> Why is support of postcoordination needed in SKOS? Because without you
> cannot specify the set and order of concepts that was used to index a
> resource! How would you say person <P> indexed resource <R> with
> concepts <C1> and <C2> at time <T>? With the proposed enhancement to the
> current draft you can say it without additional classes and properties
> or even reification:
> 
> <R> skos:subject _:x .
> _:x a skos:Collection ;
>   dc:creator <P> ;
>   skos:member <C1> ;
>   skos:member <C1> .
> 
> Actually the statement says "Ressource <R> is indexed with a set of
> concepts <C1> and <C2> that was created at time <T> by person <P>" - but
> in practise it's the same.
> 
> Greetings,
> Jakob
> 
> [1] http://www.w3.org/2004/02/skos/mapping/spec/
> 
> 
> --
> Verbundzentrale des GBV (VZG)
> Digitale Bibliothek - Jakob Vo▀
> Platz der Goettinger Sieben 1
> 37073 Goettingen - Germany
> +49 (0)551 39-10242
> http://www.gbv.de
> jakob.voss@gbv.de
> 
> 


-- 
Jakob Vo▀ <jakob.voss@gbv.de>, skype: nichtich
Verbundzentrale des GBV (VZG) / Common Library Network
Platz der Goettinger Sieben 1, 37073 G÷ttingen, Germany
+49 (0)551 39-10242, http://www.gbv.de
Received on Monday, 10 March 2008 13:38:52 GMT

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