SKOS

SKOS or Simple Knowledge Organisation Systems is a family of formal languages designed for representation of thesauri, classification schemes, taxonomies, subject-heading systems, or any other type of structured controlled vocabulary. SKOS is built upon RDF and RDFS, and its main objective is to enable easy publication of controlled structured vocabularies for the Semantic Web. SKOS is currently developed within the W3C framework.

History

SWAD-Europe (2002-2004)

SKOS was first developed as an output of the Thesaurus Activity Work Package, in the Semantic Web Advanced Development for Europe (SWAD-Europe) project [ [http://www.w3.org/2001/sw/Europe/ SWAD-Europe] ] . SWAD-Europe was funded by the European Community, and part of the Information Society Technologies programme. The project was designed to support W3C's Semantic Web Activity through research, demonstrators and outreach efforts conducted by the five project partners, ERCIM, the [http://www.ilrt.bris.ac.uk/ ILRT] at Bristol University, HP Labs, CCLRC and Stilo [ [http://www.stilo.com Stilo Home Page] ] .The first release of SKOS Core and SKOS Mapping were published at the end of 2003, along with other deliverables on RDF encoding of multilingual thesauri [ [http://www.w3c.rl.ac.uk/SWAD/deliverables/8.3.html SWAD-Europe Deliverable 8.3 : RDF Encoding of Multilingual Thesauri] ] and thesaurus mapping [ [http://www.w3c.rl.ac.uk/SWAD/deliverables/8.4.html SWAD-Europe Deliverable 8.4 : Inter-Thesaurus Mapping] ] .

Semantic Web Activity (2004-2005)

Following the termination of SWAD-Europe, SKOS effort was supported by the W3C Semantic Web Activity [ [http://www.w3.org/2001/sw/ W3C Semantic Web Activity] ] in the framework of the Best Practice and Deployment Working Group [ [http://www.w3.org/2004/03/thes-tf/mission W3C Semantic Web Best Practice and Deployment Working Group : Porting Thesauri Task Force] ] . During this period, focus was put both on consolidation of SKOS Core, and development of practical guidelines for porting and publishing thesauri for the Semantic Web.

Current Status and Roadmap (2006-2008)

SKOS is a work in progress, and the main published documents — the SKOS Core Guide [ [http://www.w3.org/TR/swbp-skos-core-guide SKOS Core Guide] W3C Working Draft 2 November 2005] , the SKOS Core Vocabulary Specification [ [http://www.w3.org/TR/swbp-skos-core-spec SKOS Core Vocabulary Specification] W3C Working Draft 2 November 2005] , and the Quick Guide to Publishing a Thesaurus on the Semantic Web [ [http://www.w3.org/TR/swbp-thesaurus-pubguide Quick Guide to Publishing a Thesaurus on the Semantic Web] W3C Working Draft 17 May 2005] — have W3C Working Draft status. The main editors of SKOS are Alistair Miles [ [http://purl.org/net/aliman Alistair Miles Home Page] ] and Dan Brickley [ [http://danbri.org/ Dan Brickley Home Page] ] .

The new Semantic Web Deployment Working Group [ [http://www.w3.org/2006/07/SWD/ W3C Semantic Web Deployment Working Group] ] , chartered for two years (May 2006 - April 2008), has put in its charter to push SKOS forward on the W3C Recommendation track. The roadmap projects SKOS as a Candidate Recommendation by the end of 2007, and as a Proposed Recommendation in the first quarter of 2008. The main issues to solve are determining its precise scope of use, and its articulation with other RDF languages and standards used in libraries (such as Dublin Core) [ [http://isegserv.itd.rl.ac.uk/public/skos/press/dc2006/camera-ready-paper.pdf SKOS: Requirements for Standardization] . The paper by Alistair Miles presented in October 2006 at the International Conference on Dublin Core and Metadata Applications.] [ [http://purl.org/net/retrieval Retrieval and the Semantic Web, incorporating a Theory of Retrieval Using Structured Vocabularies] . Dissertation on the theory of retrieval using structured vocabularies by Alistair Miles.] .

Community and Participation

All development work is carried out via the [mailto:[e-mail] [e-mail] mailing list] which is a completely open and publicly archived [ [http://lists.w3.org/Archives/Public/public-esw-thes/ [e-mail] online archive] . Archives of mailing list used for SKOS development.] mailing list devoted to discussion of issues relating to knowledge organisation systems, information retrieval and the Semantic Web. Anyone may participate informally in the development of SKOS by joining the discussions on [e-mail] - informal participation is warmly welcomed. Anyone who works for a [http://www.w3.org/Consortium/join W3C member] organisation may formally participate in the development process by joining the [http://www.w3.org/2006/07/SWD/ Semantic Web Deployment Working Group] - this entitles individuals to edit specifications and to vote on publication decisions.

SKOS components

SKOS is designed as a modular and extensible family of languages, and in a way that its use and implementation should be as simple as possible.

SKOS Core

SKOS Core [ [http://www.w3.org/2004/02/skos/core/ SKOS Core] ] defines the classes and properties sufficient to represent the common features found in a standard thesaurus. It is based on a concept-centric view of the vocabulary, where primitive objects are not terms, but abstract concepts represented by terms. Each SKOS concept is defined as an RDF resource. Each concept can have RDF properties attached, including:

* one or more preferred index terms (at most one in each natural language)
* alternative terms or synonyms
* definitions and notes, with specification of their language.

Concepts can be organized in hierarchies using broader-narrower relationships, or linked by non-hierarchical (associative) relationships.Concepts can be gathered in concept schemes, to provide consistent and structured sets of concepts, representing whole or part of a controlled vocabulary.

These features represent the stable part of SKOS Core. Other elements of the vocabulary are still considered unstable.

SKOS Mapping

SKOS Mapping [ [http://www.w3.org/2004/02/skos/mapping/ SKOS Mapping] ] is intended to provide a vocabulary to express matching (exact or fuzzy) of concepts from one concept scheme to another. This part of SKOS has been developed in the SWAD-Europe project and currently has no official home. It is maintained informally by SKOS editors.

SKOS Extensions

SKOS Extensions [ [http://www.w3.org/2004/02/skos/extensions/ SKOS Extensions] ] are intended to provide ways to declare relationships between concepts with more specific semantics than the simple "broader-narrower", such as class-instance or partitive relationships. Like SKOS Mapping, this part is likely to stay in standby mode until SKOS Core is completed as a W3C Recommendation

Applications

*Some important vocabularies have been migrated into SKOS format and are available in the public domain, including AGROVOC and GEMET.
*SKOS has been used as the language for the thesauri used in the SWED Environmental Directory [ [http://www.swed.org.uk/swed Semantic Web Environmental Directory] ] developed in the SWAD-Europe project framework.
*A way to convert thesauri to SKOS [ [http://thesauri.cs.vu.nl/eswc06/ A Method to Convert Thesauri to SKOS] ] , with examples including the MeSH thesaurus, has been outlined by the Vrije Universiteit Amsterdam.
*Subject classification using DITA and SKOS has been developed by IBM. [ [http://www-128.ibm.com/developerworks/xml/library/x-dita10/ Subject classification using DITA and SKOS] by IBM developerWorks.]
*SKOS is used to represent geographical feature types in the GeoNames ontology.

Tools

*ThManager [ [http://thmanager.sourceforge.net/ ThManager] an Open Source Tool for creating and visualizing SKOS RDF vocabularies.] is a Java open-source application for creating and visualizing SKOS vocabularies.
*The W3C provides an experimental on-line validation service [ [http://www.w3.org/2004/02/skos/core/validation SKOS Core Validation Service] ] .
*SKOS files can also be imported and edited in RDF-OWL editors such as Protégé or SWOOP developed by Mindswap [ [http://www.mindswap.org/2004/SWOOP/ SWOOP] A Hypermedia-based Featherweight OWL Ontology Editor, developed by Mindswap - Maryland Information and Network Dynamics Lab Semantic Web Agents Project ] .
*SKOS synonyms can be transformed from WordNet RDF format using an XSLT stylesheet see [http://www.w3.org/TR/wordnet-rdf W3C RDF]

Relationships with other standards

SKOS and Thesaurus standards

SKOS development has involved experts from both RDF and library community, and SKOS intends to allow easy migration of thesauri defined by standards such as NISO Z39.19 - 2005 [ [http://www.niso.org/standards/ NISO Standards] Z39.19 - 2005 : Guidelines for the Construction, Format, and Management of Monolingual Controlled Vocabularies ] or ISO 5964:1985 [ [http://www.collectionscanada.ca/iso/tc46sc9/standard/5964e.htm ISO 5964:1985] Guidelines for the establishment and development of multilingual thesauri] .

SKOS and other Semantic Web standards

SKOS is intended to provide a way to make a legacy of concept schemes available to Semantic Web applications, simpler than the more complex ontology language, OWL. OWL is intended to express complex conceptual structures, which can be used to generate rich metadata and support inference tools. However, constructing useful web ontologies is demanding in terms of expertise, effort, and cost. In many cases, this type of effort might be superfluous or unsuited to requirements, and SKOS might be a better choice. The extensibility of RDF makes possible further incorporation or extension of SKOS vocabularies into more complex vocabularies, including OWL ontologies.

See also

* Glossary
* Knowledge representation
* Metadata
* Metadata registry
* W3C
* Taxonomy
* [http://www.loc.gov/standards/mads/ Metadata Authority Description Schema (MADS)] , an XML schema for an authority element set that may be used to provide metadata about agents (people, organizations), events, and terms (topics, geographics, genres, etc.).

External links

* [http://www.w3.org/2004/02/skos/ W3C SKOS Home Page]
* [http://www.idealliance.org/proceedings/xtech05/papers/03-04-01/ Presentation of SKOS at XTech 2005 Conference]

References