RE: [SKOS] ISSUE 77 and ISSUE-40: proposal for postcoordination

Here's a few thoughts on "post-coordination".

Following the strict view that "post-coordination" means combining concepts
at query time via "Boolean" operators, here are some examples of expressing
such queries via SPARQL [1].

# A query for X AND Y
BASE <http://example.com/ns/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
SELECT ?document 
WHERE { ?document dc:subject <X>, <Y> }

# A query for X OR Y
BASE <http://example.com/ns/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
SELECT ?document 
WHERE { { ?document dc:subject <X> } UNION { ?document dc:subject <Y> } }

# A query for X NOT Y
BASE <http://example.com/ns/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
SELECT ?document 
WHERE {
  ?document dc:subject <X> 
  OPTIONAL { ?document dc:subject ?y FILTER ( ?y = <Y> ) }
  FILTER ( !bound(?y) ) 
}
 
I'm not entirely sure about the last one (I haven't tried it), but the first
two should be OK.

Cheers,

Alistair.

[1] http://www.w3.org/TR/rdf-sparql-query/

--
Alistair Miles
Senior Computing Officer
Image Bioinformatics Research Group
Department of Zoology
The Tinbergen Building
University of Oxford
South Parks Road
Oxford
OX1 3PS
United Kingdom
Web: http://purl.org/net/aliman
Email: alistair.miles@zoo.ox.ac.uk
Tel: +44 (0)1865 281993


> -----Original Message-----
> From: public-esw-thes-request@w3.org [mailto:public-esw-thes-
> request@w3.org] On Behalf Of Antoine Isaac
> Sent: 18 March 2008 08:05
> To: Antoine Isaac
> Cc: Jakob Voss; public-esw-thes@w3.org; public-swd-wg@w3.org
> Subject: [SKOS] ISSUE 77 and ISSUE-40: proposal for postcoordination
> 
> 
> Hi Jakob,
> 
> Coming back to your real problem.
> For pre-coordination for the moment I don't have a definitive
> proposition, but for post-coordination, why don't you use rdf:Bag and
> rdf:Alt [1]? Has it been proposed before?
> 
> rdf:Bag intended meaning seems to fit quite well the semantics of AND
> in
> post-coordination, and rdf:Alt the semantics of OR
> 
> For instance your
> >  #R skos:subject x:holiday .
> >  #R skos:subject x:y2k8 .
> would be represented as
> #R skos:subject _:z .
> _:z rdf:type rdf:Bag .
> _:z rdf:_1 x:holiday .
> _:z rdf:_2 x:y2k8  .
> 
> Notice that this lets application developers the care of handling
> these.
> But that's a bit what happens with post-coordination anyway.
> 
> So what do you think this proposal is usable for you? I do believe it
> is
> simpler, and appropriately re-uses existing RDF solutions (I think the
> examples given in [1] are really close to what you want to achieve)
> 
> Notice we MAY want to assign semantics for this proposal pattern, e.g.
> saying that all the members of the bag are the skos:subject of the
> document. But I'm not sure this actually fits the intended semantics of
> post-coordination. If a document is about a combination of concept in a
> post-coordination-based search system, it is not supposed to be "fully"
> about each concept.
> 
> Notice also that I don't have time, but it might be possible to use RDF
> containers for pre-coordination. Maybe more will come in the near
> future...
> 
> Cheers,
> 
> Antoine
> 
> [1] http://www.w3.org/TR/rdf-primer/#containers
> 
> > Hi Jakob,
> >
> > Your comment is a very valid one.
> > Actually there is a closely related issue, ISSUE-40
> ConceptCoordination
> > Initially it is about pre-coordination, but I do believe that the
> same
> > representation mechanisms can be used for both problems (at least in
> > an RDF-oriented view)
> >
> > About the content of your proposal: I find the pattern quite
> > meaningful, but am really not sure that using Collections is optimal.
> > What  I'm afraid of is that in their current uses, Collections are
> > rather interpreted as 'unions' of concepts, while some coordination
> > cases makes me really think of 'intersection'(at least from a boolean
> > query perspective)
> > But it may be worthwile to investigate this further...
> >
> > Best,
> >
> > Antoine
> >
> > [1] http://www.w3.org/2006/07/SWD/track/issues/40
> >
> >
> > -------- Message d'origine--------
> > De: public-esw-thes-request@w3.org de la part de Jakob Voss
> > Date: lun. 10/03/2008 04:22
> > À: 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 Voß
> > Platz der Goettinger Sieben 1
> > 37073 Goettingen - Germany
> > +49 (0)551 39-10242
> > http://www.gbv.de
> > jakob.voss@gbv.de
> >
> >
> 
> 
>

Received on Wednesday, 4 June 2008 09:15:03 UTC