- From: Ed Summers <ehs@pobox.com>
- Date: Tue, 19 Aug 2008 01:00:58 -0400
- To: "SWD WG" <public-swd-wg@w3.org>
I took an action at the last face to face to offer up some text describing why ISSUE-40 Concept Coordination was postponed. http://www.w3.org/2008/04/22-swd-minutes.html#action02 It's been a busy summer, and a long time coming, but here it is. If you have the energy please give it a read over to make sure that 1) I characterize the difference between pre and post-coordination correctly; 2) the alternatives including ex:coordinationOf, owl:unionOf and SPARQL are sound ; and that 3) I captured the spirit of this decision appropriately. //Ed 4.4 Coordinating Concepts Indexing practices involving thesauri and other KOS often include the notion of coordination. Coordination is an activity in which concepts from a KOS are combined together. In general there are two kinds of coordination: pre-coordination [1] and post-coordination [2]. The key distinction between the two hinges on when the actual coordination occurs in relation to an information retrieval event. Pre-coordination is done prior to information retrieval, by a KOS maintainer, or by an indexer who is using a KOS. For example, if a concept scheme includes a concept for "Bicycle Repair" it is considered to be pre-coordinated concept of the concept "Bicycle" and "Repair". In addition it is also considered to be pre-coordination when an indexer takes two existing concepts from a concept scheme, like "Bicycles" and "Repairing", and combines them with a given syntax like "Bicycles--Repairing" to index a particular document. Post-coordination on the other hand is performed as part of an information retrieval task. For example if a given document is indexed with two distinct concepts "Bicycles" and "Repairing" and a user decides to perform a search for all documents that are indexed with "Bicycles" and "Repairing". SKOS has some facilities for representing concept coordination. The most basic form of pre-coordination is certainly expressible with SKOS: ex:bicycleRepair a skos:Concept ; skos:prefLabel "Bicycle Repair"@en . Post-coordination as an information retrieval activity also lends itself to representation as a SPARQL query. For example, given two distinct concepts: ex:bicycles a skos:Concept ; skos:prefLabel "Bicycles"@en . ex:repairing a skos:Concept ; skos:prefLabel "Repairing"@en . you could construct a SPARQL query to return only the documents that are indexed with both concepts: SELECT ?document WHERE { ?document dc:subject ex:bicycles . ?document dc:subject ex:repairing . } However the SKOS vocabulary itself does not provide any mechanism for expressing that a given concept consists of a pre-coordination of other concepts. Of course it is perfectly feasible to extend SKOS [3] to establish a pattern for representing coordinated concepts. For example it has been suggested [4] that a new property such as <code>ex:coordinationOf</code> could be established: ex:coordinationOf a rdf:Property ; rdfs:domain skos:Concept ; rdfs:range rdf:List . Which could then be used in assertions such as: ex:bicyclesRepairing a skos:Concept ; ex:coordinationOf (ex:bicycles, ex:repairing) ; skos:prefLabel "Bicycles--Repairing"@en . It has also been suggested that OWL itself could be used to coordinate concepts: ex:bicyclesRepairing a skos:Concept ; owl:unionOf (ex:bicycles, ex:repairing) ; skos:prefLabel "Bicycles--Repairing"@en. However, established patterns for pre-coordinations of this kind have not yet emerged in the SKOS community. <code>ex:coordinationOf</code> (or some equivalent extension), and the ramifications of using SKOS with OWL [5] have not been explored fully enough yet to warrant inclusion in the SKOS Reference [6], and consequently in this Primer. Rather than commit to a design pattern that hasn't been proven useful, the Semantic Web Deployment Group decided to postpone the issue of coordination [7], to allow extension patterns to organically emerge as SKOS is deployed. The hope is that as successful patterns are established they can be documented as a W3C Note or some equivalent. @@ TODO include info about wiki/discussion list here or in Specialization section? @@ [1] http://www.willpowerinfo.co.uk/glossary.htm#pre-coord [2] http://www.willpowerinfo.co.uk/glossary.htm#post-coord [3] http://www.w3.org/TR/skos-primer/#secskosspecialization [4] http://isegserv.itd.rl.ac.uk/public/skos/press/dc2006/coordination.html [5] http://www.w3.org/TR/skos-primer/#secskosowl [6] http://www.w3.org/TR/skos-reference/ [7] http://www.w3.org/2006/07/SWD/track/issues/40
Received on Tuesday, 19 August 2008 05:01:34 UTC