SKOS
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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.
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[edit] History
[edit] 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 [1]. 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 ILRT at Bristol University, HP Labs, CCLRC and Stilo [2] . 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 [3] and thesaurus mapping [4].
[edit] Semantic Web Activity (2004-2005)
Following the termination of SWAD-Europe, SKOS effort was supported by the W3C Semantic Web Activity [5] in the framework of the Best Practice and Deployment Working Group [6]. 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.
[edit] Current Status and Roadmap (2006-2008)
SKOS is a work in progress, and the main published documents — the SKOS Core Guide [7], the SKOS Core Vocabulary Specification [8], and the Quick Guide to Publishing a Thesaurus on the Semantic Web [9] — have W3C Working Draft status. The main editors of SKOS are Alistair Miles [10] and Dan Brickley [11].
The new Semantic Web Deployment Working Group [12], 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) [13][14].
[edit] Community and Participation
All development work is carried out via the public-esw-thes@w3.org mailing list which is a completely open and publicly archived [15] 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 public-esw-thes@w3.org - informal participation is warmly welcomed. Anyone who works for a W3C member organisation may formally participate in the development process by joining the Semantic Web Deployment Working Group - this entitles individuals to edit specifications and to vote on publication decisions.
[edit] 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.
[edit] SKOS Core
SKOS Core [16] 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:
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.
[edit] SKOS Mapping
SKOS Mapping [17] 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.
[edit] SKOS Extensions
SKOS Extensions [18] 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
[edit] Applications
[edit] Tools
[edit] Relationships with other standards
[edit] 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 [25] or ISO 5964:1985 [26].
[edit] 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.
