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{{short description|W3C recommendation}}
{{Infobox technology standard
| title = SKOS
| long_name =Simple Knowledge Organization System
| native_name =
| native_name_lang =
| image =
| caption =
| status = Published ([[W3C Recommendation]])
| year_started ={{Start date and age|1997}}
| version =[https://www.w3.org/2009/08/skos-reference/skos.html Core], [https://www.w3.org/TR/skos-reference/ Reference], [http://www.w3.org/TR/skos-reference/skos.rdf RDF], [https://www.w3.org/TR/skos-primer/ Primer]
| version_date ={{Start date and age|18|8|2009}}
| preview =
| preview_date =
| organization = [[World Wide Web Consortium]] (W3C)
| committee =[https://www.w3.org/2006/07/SWD/ Semantic Web Deployment Working Group]
| base_standards = [[Resource Description Framework|RDF]]
| related_standards =[[RDFa]], [[Web Ontology Language|OWL]], [[ISO 25964]], [[Dublin Core]]
| abbreviation = SKOS
| ___domain = [[Semantic Web]]
| license =
| website = {{URL|https://www.w3.org/TR/skos-reference/}}
|first_published=
|authors=[[Alistair Miles]], [[Sean Bechhofer]]
|series=
|editors=
}}
'''Simple Knowledge Organization System''' ('''SKOS''') is a [[W3C recommendation]] designed for representation of [[Thesaurus (information retrieval)|thesauri]], [[classification scheme]]s, [[Taxonomy (general)|taxonomies]], [[Authority control|subject-heading systems]], or any other type of structured [[controlled vocabulary]]. SKOS is part of the [[Semantic Web]] family of standards built upon [[Resource Description Framework|RDF]] and [[RDF Schema|RDFS]], and its main objective is to enable easy publication and use of such vocabularies as [[linked data]].
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=== DESIRE II project (1997–2000) ===
The most direct ancestor to SKOS was the RDF Thesaurus work undertaken in the second phase of the EU DESIRE project <ref name="Desire Project">{{Citation |
=== LIMBER (1999–2001) ===
SKOS built upon the output of the Language Independent Metadata Browsing of European Resources (LIMBER) project funded by the [[European Community]], and part of the [[Information Society Technologies]] programme. In the LIMBER project [[CCLRC]] further developed an [[Resource Description Framework|RDF]] thesaurus interchange format<ref>
=== SWAD-Europe (2002–2004) ===
SKOS as a distinct initiative began in the SWAD-Europe project, bringing together partners from both DESIRE, SOSIG (ILRT) and LIMBER (CCLRC) who had worked with earlier versions of the schema. It was developed in the Thesaurus Activity Work Package, in the Semantic Web Advanced Development for Europe (SWAD-Europe) project.<ref>
=== Semantic web activity (2004–2005) ===
Following the termination of SWAD-Europe, SKOS effort was supported by the W3C Semantic Web Activity<ref>
=== Development as W3C Recommendation (2006–2009) ===
The SKOS main published documents — the SKOS Core Guide,<ref>[http://www.w3.org/TR/swbp-skos-core-guide SKOS Core Guide] W3C Working Draft 2 November 2005</ref> the SKOS Core Vocabulary Specification,<ref>[http://www.w3.org/TR/swbp-skos-core-spec SKOS Core Vocabulary Specification] W3C Working Draft 2 November 2005</ref> and the Quick Guide to Publishing a Thesaurus on the Semantic Web<ref>[http://www.w3.org/TR/swbp-thesaurus-pubguide Quick Guide to Publishing a Thesaurus on the Semantic Web] W3C Working Draft 17 May 2005</ref> — were developed through the W3C Working Draft process. Principal editors of SKOS were Alistair Miles,<ref>
The Semantic Web Deployment Working Group,<ref>
=== Formal release (2009) ===
On August 18, 2009, [[W3C]] released the new standard that builds a bridge between the world of [[Knowledge organization system|knowledge organization systems]] – including thesauri, classifications, subject headings, taxonomies, and [[folksonomy|folksonomies]] – and the [[linked data]] community, bringing benefits to both. Libraries, museums, newspapers, government portals, enterprises, social networking applications, and other communities that manage large collections of books, historical artifacts, news reports, business glossaries, blog entries, and other items can now use SKOS<ref>
=== Historical view of components ===
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In addition to the reference itself, the SKOS Primer (a W3C Working Group Note) summarizes the Simple Knowledge Organization System.
The SKOS<ref>
* one or more preferred [[index term]]s (at most one in each natural language)
* alternative terms or [[synonym]]s
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=== Element categories ===
The principal element categories of SKOS are concepts, labels, notations, documentation, semantic relations, mapping properties, and collections. The associated
{| border="1" class="wikitable"
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=== Concepts ===
The SKOS vocabulary is based on concepts. Concepts are the units of thought—ideas, meanings, or objects and events (instances or categories)—which underlie many knowledge organization systems. As such, concepts exist in the mind as abstract entities which are independent of the terms used to label them. In SKOS, a <code>Concept</code> (based on the OWL <code>Class</code>) is used to represent items in a knowledge organization system (terms, ideas, meanings, etc.) or such a system's conceptual or organizational structure.<ref name=":0">{{cite web |date=2009-08-18 |title=SKOS Simple Knowledge Organization System Reference#Concepts |url=https://www.w3.org/TR/2009/NOTE-skos-primer-20090818/#secconcept |access-date=2024-02-28 |website=www.w3.org |language=en |id=W3C NOTE skos-primer-2009/#secconcept}}</ref>
A <code>ConceptScheme</code> is analogous to a vocabulary, thesaurus, or other way of organizing concepts. SKOS does not constrain a concept to be within a particular scheme, nor does it provide any way to declare a complete scheme—there is no way to say the scheme consists only of certain members. A topConcept is (one of) the upper concept(s) in a hierarchical scheme.
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Each SKOS <code>label</code> is a string of [[Unicode]] characters, optionally with language tags, that are associated with a concept. The <code>prefLabel</code> is the preferred human-readable string (maximum one per language tag), while <code>altLabel</code> can be used for alternative strings, and <code>hiddenLabel</code> can be used for strings that are useful to associate, but not meant for humans to read.
A SKOS <code>notation</code> is similar to a label, but
=== Documentation ===
The Documentation or Note properties provide basic information about SKOS concepts. All the
Any of these SKOS Documentation properties can refer to several object types: a literal (e.g., a string); a resource node that has its own properties; or a reference to another document, for example using a URI. This enables the documentation to have its own [[metadata]], like creator and creation date.
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The property <code>related</code> simply makes an association relationship between two concepts; no hierarchy or generality relation is implied. The properties <code>broader</code> and <code>narrower</code> are used to assert a direct hierarchical link between two concepts. The meaning may be unexpected; the relation <code><A> broader <B></code> means that A has a broader concept called B—hence that B is broader than A. Narrower follows in the same pattern.
While the casual reader might expect broader and narrower to be [[Transitive relation|transitive]] properties, SKOS does not declare them as such. Rather, the properties <code>broaderTransitive</code> and <code>narrowerTransitive</code> are defined as transitive super-properties of broader and narrower. These super-properties are (by convention) not used in declarative SKOS statements. Instead, when a broader or narrower relation is used in a triple, the corresponding transitive super-property also holds; and transitive relations can be inferred (and queried) using these super-properties.
=== Mapping ===
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SKOS mapping properties are intended to express matching (exact or fuzzy) of concepts from one concept scheme to another, and by convention are used only to connect concepts from different schemes. The concepts <code>relatedMatch</code>, <code>broadMatch</code>, and <code>narrowMatch</code> are a convenience, with the same meaning as the semantic properties <code>related</code>, <code>broader</code>, and <code>narrower</code>. (See previous section regarding the meanings of broader and narrower.)
The property <code>relatedMatch</code> makes a simple associative relationship between two concepts. When concepts are so closely related that they can generally be used interchangeably, <code>exactMatch</code> is the appropriate property (<code>exactMatch</code> relations are transitive, unlike any of the other Match relations). The <code>closeMatch</code> property that indicates concepts that only sometimes can be used interchangeably, and so it is not a transitive property.
=== Concept collections ===
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== Applications ==
*Some important vocabularies have been migrated into SKOS format and are available in the public ___domain, including [[EuroVoc]], [[AGROVOC]] and [[GEMET]]. [[Library of Congress Subject Headings]] (LCSH) also support the SKOS format.<ref>
*SKOS has been used as the language for the thesauri used in the [[SWED Environmental Directory]]<ref>
*A way to convert thesauri to SKOS,<ref>
*Subject classification using [[Darwin Information Typing Architecture|DITA]] and SKOS has been developed by [[IBM]].<ref>[http://www-128.ibm.com/developerworks/xml/library/x-dita10/ Subject classification using
*SKOS is used to represent geographical feature types in the [[GeoNames]] ontology.
== Tools ==
* Unilexicon<ref>[https://unilexicon.com/ Unilexicon] web based visual taxonomy editor</ref> is a web based visual editor and [[Taxonomy for search engines|taxonomy]] manager for authoring controlled vocabularies with tagging integration and JSON API. Its primary visualisation uses [[hyperbolic tree]].
* ThesauRex is an open-source, web-based SKOS editor. It is limited to broader/narrower relations among concepts and offers tree-based interaction and with thesauri and drag&drop creation of new thesauri based on a master thesaurus.<ref>{{cite web|url=https://github.com/eScienceCenter/ThesauRex|title=eScienceCenter/ThesauRex|date=22 March 2020|website=GitHub}}</ref>
* Mondeca's Intelligent Topic Manager (ITM) is a full-featured SKOS-compliant solution for managing taxonomies, thesauri, and other controlled vocabularies.
*Opentheso is an open source web-based thesaurus management system compliant with ISO 25964:2011 and ISO 25964-2:2012 standards (Information and Documentation. Thesauri and Interoperability with other vocabularies). It offers SKOS and csv exports and imports, REST and SOAP web services and manages persistent identifiers (ARK). It has been developed at the French National Center for Scientific Research since 2007. It is currently used by the French archaeological libraries network Frantiq and by research teams and by the Hospices Civils de Lyon as a collaborative thesaurus management tool. It can be downloaded on github.<ref>{{Cite web | url=http://opentheso.healthandco.fr/opentheso/opentheso.xhtml | title=Opentheso - Copyright | access-date=2018-04-04 | archive-date=2020-08-07 | archive-url=https://web.archive.org/web/20200807064751/http://opentheso.healthandco.fr/opentheso/opentheso.xhtml | url-status=dead }}</ref>
* OpenSKOS is a web service-based approach to publication, management and use of vocabulary data that can be mapped to SKOS. Its source code is available on GitHub. It includes [[CRUD]] like [[RESTful]] operations on SKOS concepts and a web-based editor for searching and editing concepts. It was developed by Picturae and funded by the Dutch heritage fond CATCHPlus.
* [[TemaTres]] Vocabulary Server<ref>[http://www.vocabularyserver.com TemaTres] is an open source web-based vocabulary server for managing controlled vocabularies, taxonomies and thesauruses</ref> is an open source web-based vocabulary server for managing controlled vocabularies, taxonomies and thesauruses and
* ThManager<ref>[
* The W3C provides an experimental on-line validation service.<ref>
* Vocbench<ref>
* SKOS files can also be imported and edited in RDF-OWL editors such as [[Protege (software)|Protégé]], SKOS Shuttle and TopBraid Composer.
* SKOS synonyms can be transformed from [[WordNet]] RDF format using an [[XSLT]] style sheet; see W3C RDF
* PoolParty<ref>[http://www.poolparty.biz/ PoolParty] is a thesaurus management system and a SKOS editor for the Semantic Web.</ref> is a commercial-quality thesaurus management system and a SKOS editor for the Semantic Web including text analysis functionalities and [[Linked Data]] capabilities.
* qSKOS<ref>[https://github.com/cmader/qSKOS/ qSKOS] is an open-source tool for SKOS vocabulary quality assessment.</ref> is an open-source tool for performing quality assessment of SKOS vocabularies by checking against a quality issue catalog.
* SKOSEd<ref>[http://code.google.com/p/skoseditor/ SKOSEd] SKOS plugin for Protege 4</ref> is an open source plug-in for the Protégé 4<ref>Protégé 4 Protégé 4 OWL editor</ref> [[Web Ontology Language|OWL]] ontology editor that supports authoring SKOS vocabularies. SKOSEd has an accompanying SKOS API<ref>[
* Model Futures SKOS Exporter<ref>
* Lexaurus<ref>[
* SKOS Shuttle<ref>
* TopBraid Enterprise Vocabulary Net (EVN)<ref>
* Thesaurus Master, for creating, developing, and maintaining taxonomies and thesauri, is part of Access Innovations' Data Harmony knowledge management software line. It offers SKOS-compliant export.
* Fluent Editor 2014 – an ontology editor which allows users to work and edit directly OWL annotations and SKOS. Annotations will be processed also for referenced ontologies as well as imported/exported to OWL/RDF and can be processed on the server.
* Smartlogic Semaphore Ontology Editor – a SKOS and SKOS-XL based ontology editor which allows creating models based strictly on the SKOS standards.
== Data ==
There are publicly available SKOS data sources.
* SKOS Datasets wiki<ref>
== Relationships with other standards ==
=== Metamodel ===
The SKOS metamodel is broadly compatible with the data model of [[ISO 25964-1]] – Thesauri for Information Retrieval. This data model can be viewed and downloaded from the website for [[ISO 25964]].<ref name="niso.org">
[[File:Skos metamodel.png|thumb|Semantic model of the information elements of SKOS]]
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* [http://www.w3.org/2004/02/skos/ W3C SKOS Home Page]
* [http://www.w3.org/TR/2009/NOTE-skos-primer-20090818 W3C Simple Knowledge Organization System Primer]
* [
* [http://www.w3.org/News/2009#item35 W3C Invites Implementations of SKOS (Simple Knowledge Organization System) Reference; Primer Also Published]
* [http://demo.semantic-web.at:8080/SkosServices/index SKOS Validator and Zthes Converter] {{Webarchive|url=https://web.archive.org/web/20100211135151/http://demo.semantic-web.at:8080/SkosServices/index |date=2010-02-11 }}
{{Semantic Web}}
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[[Category:Knowledge representation]]
[[Category:Semantic Web]]
[[Category:
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