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SKOS or Simple Knowledge Organisation System 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 in the W3C framework.
History
SWAD-Europe (2002-2004)
SKOS has been first an output of the Thesaurus Activity Work Package, in the Semantic Web Advanced Development for Europe project (SWAD-Europe). SWAD-Europe project 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, Bristol University, HP Labs, CCLRC and Stilo. The first release of SKOS-Core and SKOS-Mapping were published at the end of 2003, along with other deliverables about Inter-Thesaurus Mapping and RDF Encoding of Multilingual Thesauri.
Semantic Web Activity (2004-2005)
Following the termination of SWAD-Europe, SKOS effort was supported by the Semantic Web Best Practice and Deployment Working Group, a part of the W3C's Semantic Web Activity. 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 (2006)
SKOS is a work in progress, and the main published documents, the 'SKOS Core Guide', the 'SKOS Core Vocabulary Specification', and the 'Quick Guide to Publishing a Thesaurus on the Semantic Web' have W3C Working Draft status. Some important vocabularies have been migrated in SKOS format, including AGROVOC and GEneral Multilingual Environmental Thesaurus GEMET
Developement Roadmap (2006-2008)
The new 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 is to have SKOS as a Candidate Recommendation by the end of 2007, and Proposed Recommendation in the first quarter of 2008.
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 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 a RDF resource. To each concept can be attached RDF properties : one or more preferred 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. The above features represent the stable elements of SKOS-Core, other are still considered as unstable.SKOS Mapping
SKOS Mapping provides 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 main editors Alistair Miles and Dan Brickley.SKOS Extensions
SKOS extensions were 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 of SKOS is likely to stay in standby until SKOS Core is completed as a W3C RecommendationRelationships 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 (Guidelines for the Construction, Format, and Management of Monolingual Controlled Vocabularies) or ISO 5964:1985 Guidelines for the establishment and development of multilingual thesauri.SKOS and OWL
Links
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