SKOS Core Vocabulary Specification

Abstract

SKOS Core provides a model for expressing the basic structure and content of concept schemes (thesauri, classification schemes, subject heading lists, taxonomies, terminologies, glossaries and other types of controlled vocabulary).

The SKOS Core Vocabulary is an application of the Resource Description Framework (RDF), that can be used to express a concept scheme as an RDF graph. Using RDF allows data to be linked to and/or merged with other RDF data by semantic web applications.

This specification is intended to provide the authoritative human-readable account of the SKOS Core Vocabulary, and to reflect the state of the of SKOS Core Vocabulary at the time of publication. The content of the term summary tables in this specification is generated from the SKOS Core Vocabulary RDF/OWL description.

This document should be read in conjunction with the SKOS Core Guide.

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Status of this Document

This section describes the status of this document at the time of its publication.

This document is an Editor's Draft for review by the Semantic Web Best Practices and Deployment Working Group (hereafter 'the Working Group') and the participants of the public-esw-thes@w3.org mailing list and is subject to change without notice. This document has no formal standing within W3C. Please consult the Working Group's home page and the W3C technical reports index for information about the latest publications by this group. This document may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document is published by the Semantic Web Best Practices and Deployment Working Group, part of the W3C Semantic Web Activity. The Working Group intends the SKOS Core Vocabulary Specification to become a W3C Working Group Note. However, other outcomes are possible within the framework of the W3C process and will be considered in response to deployment experience and feedback from the W3C membership. The Working Group has discussed the potential for SKOS Core to evolve into possible future W3C Recommendation Track work items, and would value feedback on the level of formal standardization that is appropriate.

We encourage public comments. Please send comments to public-esw-thes@w3.org [archive] and start the subject line of the message with "comment:".

Publication as a Working Draft does not imply endorsement by the W3C Membership.

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Contents

• Introduction
• Guide to Term Summary Tables
• Policy Statements
  • Naming
  • Persistence
  • Change
  • Maintenance
• Classes
• Properties
• Deprecated Terms
• Change Log
• Acknowledgements

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Introduction

SKOS stands for Simple Knowledge Organisation System. The name SKOS was chosen to emphasise the goal of providing a simple yet powerful framework for expressing knowledge organisation systems in a machine-understandable way.

SKOS Core provides a model for expressing the basic structure and content of concept schemes (thesauri, classification schemes, subject heading lists, taxonomies, terminologies, glossaries and other types of controlled vocabulary).

The SKOS Core Vocabulary is an application of the Resource Description Framework (RDF). RDF provides a simple data formalism for talking about things, their properties, inter-relationships, and categories (classes). Using RDF allows data to be linked to and/or merged with other RDF data by semantic web applications. See RDF Concepts for an overview of RDF, RDF Semantics for its formal mathematical basis, and RDF Syntax for details of the RDF/XML document format used to exchange RDF data.

The SKOS Core Vocabulary is itself formally defined using RDF and OWL [OWL]. The resource http://www.w3.org/2004/02/skos/core.rdf contains the definitive SKOS Core Vocabulary RDF/OWL description.

This specification is intended to provide the authoritative human-readable account of the SKOS Core Vocabulary, and to reflect the state of the of SKOS Core Vocabulary at the time of publication. The content of the term summary tables in this specification is generated [SRC] from the SKOS Core Vocabulary RDF/OWL description on the date of publication of this document.

Because the SKOS Core Vocabulary may change (see Change Policy Statement below), there may be inconsistencies between this document and the SKOS Core Vocabulary RDF/OWL description. The latest version of the SKOS Core Vocabulary Specification should accurately reflect the current state of the SKOS Core Vocabulary RDF/OWL description, although there still may on occasion be short periods (eg. during Web site publication) during which there are minor inconsistencies.

Although the SKOS Core Vocabulary RDF/OWL description is not itself a W3C Technical Report, it is (at least for the lifetime of the Semantic Web Best Practices WG) being managed with the intent of being consistent with this document, as well as with other supporting materials published as W3C Technical Reports.

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Guide to Term Summary Tables

Each term (i.e. class or property) of the SKOS Core vocabulary is summarised in this document as a table. Each table may have the following rows:

Class or Property:
URI:	The Universal Resource Identifier.
Label:	A human-readable label.
Definition:	An explanation of the meaning of a class or property.
Comment:	Additional information about meaning and/or proper use.
Example:	An example of the use of a class or property.
Status:	The status (stability level) of the class or property.
Issued:	Date on which the class or property was issued.
Modified:	Date on which the class or property was last modified.
Super-classes:	(Classes only) any declared super-classes.
Super-properties:	(Properties only) any declared super-properties.
Domain:	(Properties only) the declared domain for the property.
Range:	(Properties only) the declared range for the property.
Additional types:	(Properties only) any declared additional types (e.g. owl:TransitiveProperty) for the property.
Inverse of:	(Properties only) any declared inverse properties.
Replaces:	Any deprecated terms which the given term has replaced in recommended usage.
Version info:	A note about the modification and/or history of a class or property.
Replaced By:	(Deprecated terms only) the term to use instead of the deprecated term.
Deprecated:	(Deprecated terms only) the date of last modification (i.e. deprecation) of the term.

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Policy Statements

N.B. The Policy Statements described in this specification are a best effort representation of the Working Group's initial thinking and intent, and are subject to the caveats described in the Status of this Document section. It is intended that this warning be removed after further discussion in subsequent iterations of this working draft. Also note that control of the SKOS Core namespace will revert to W3C control once this WG's charter expires.

Naming

The URI for the SKOS Core Vocabulary itself is:

http://www.w3.org/2004/02/skos/core

The URI for a class or property in the SKOS Core Vocabulary is constructed by appending the local name for that property or class to the URI http://www.w3.org/2004/02/skos/core#. E.g.

http://www.w3.org/2004/02/skos/core#Concept
http://www.w3.org/2004/02/skos/core#prefSymbol

The local name of a class always starts with an uppercase character. Where the local name is comprised of multiple concatenated words, the leading character of each word will be an uppercase character. E.g.

Concept
ConceptScheme

The local name of a property starts with a lowercase character. Where the local name is comprised of multiple concatenated words, the leading character of the second and each subsequent word will be an uppercase character. E.g.

subject
prefLabel
isPrimarySubjectOf

Persistence

This document, the SKOS Core Guide, the RDF description of the SKOS Core Vocabulary, and the classes and properties of the SKOS Core Vocabulary are all declared to be persistent resources, as defined at [URI Persistence Policy].

Change

Changes to SKOS Core classes and properties may occur. All changes are reported on the SKOS Change Log.

Each class or property is assigned a term status value, which indicates the stability of the resource, and the types of modification that are allowed [DCMI Namespace]. A class or property may take one of three term status values:

unstable

The term is unstable, and feedback is welcomed on it's current form and utility (analogous to 'alpha' release in software development). It may currently be poorly defined. its meaning and/or form may be expected to change at any time. Do not implement mission critical systems that depend on this term persisting in its current form. (Changes corresponding to DCMI class A, B or C may occur).

testing

The term has gone beyond the raw proposal stage, and is undergoing testing (analogous to 'beta' release in software development). This term may still change in response to feedback from testing, although it may be expected not to undergo any radical change. The cost to early implementors of changing the term will be considered, however the goal of achieving wider interoperability and long-term stability may override those considerations. (Changes corresponding to DCMI class A or B may occur)

stable

No substantial (meaning changing) alterations will take place. Implementors can expect the term to persist in its current form indefinitely. (Changes corresponding to DCMI class A may occur)

New classes or properties may be added to the SKOS Core Vocabulary at any time (changes corresponding to DCMI class D).

A class or property at any of the above status levels may be marked as deprecated, in which case instructions will be given on what to use in its place. A deprecated class property may be expected to remain unchanged indefinitely.

Maintenance

The SKOS Core Vocabulary is hosted and maintained by W3C. At the time of writing, W3C has delegated management of the SKOS Core namespace to the the Semantic Web Best Practices WG, whose chairs have in turn have delegated these responsibilities to the editors of this specification (Alistair Miles and Dan Brickley). The Working Group is committed to establishing clear expectations around the management of RDF vocabularies, through documentation of process and maintenance policies. This is itself an evolving process. Specifically, this document is itself situated within the W3C Process, and may change and evolve in the light of feedback on SKOS Core and on the SKOS Core policy statements. It should be noted that claims made by the Working Group using the (experimental) persistence and change terminology employed here have as their scope the currently chartered Working Group. They have only draft status within the wider W3C Process. W3C has not delegated to the WG any authority to make binding commitments on behalf of W3C beyond those implicit in the formal W3C Process.

The Working Group is committed to a public, consensus-driven design environment for SKOS Core, and to this end conducts SKOS-related discussion in public, in particular drawing on feedback from the Semantic Web Interest Group mailing list public-esw-thes@w3.org.

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RCS file: /w3ccvs/WWW/2004/02/skos/core.rdf,v
Working file: core.rdf
head: 1.38
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 38;	selected revisions: 38
description:
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revision 1.38
date: 2005/02/25 13:11:13;  author: ajm65;  state: Exp;  lines: +20 -4
skos:subject domain altered from foaf:Document to unconstrained.  skos:isSubjectOf range altered in same way.
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revision 1.37
date: 2005/02/09 19:07:18;  author: ajm65;  state: Exp;  lines: +16 -7
Modified the definition of skos:ConceptScheme to ''A set of concepts, optionally including statements about semantic relationships between those concepts."
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revision 1.36
date: 2004/12/17 13:43:58;  author: ajm65;  state: Exp;  lines: +11 -3
Change to skos:related - Changed the definition to mention 'associative relationships', because previous definition too broad, and also to bring in line with BS8723 definition of 'associative relationships'.
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revision 1.35
date: 2004/12/17 13:37:39;  author: ajm65;  state: Exp;  lines: +8 -2
Change to skos:OrderedCollection - The text 'where both the grouping and the ordering are meaningful' added to the definition.
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revision 1.34
date: 2004/12/17 13:34:05;  author: ajm65;  state: Exp;  lines: +9 -1
Change to skos:ConceptScheme - Reworked the definition, in line with new guide.  Concept scheme now defined as 'a *description* of a set of concepts, which may include a description of relationships between those concepts'.  This change made to make explicit the fact that semantic relationships between concepts may be part of a concept scheme. Also expresses modelling concept scheme as an information resource (hence the 'description' word added).
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revision 1.33
date: 2004/12/17 13:28:08;  author: ajm65;  state: Exp;  lines: +8 -1
Change to skos:Concept - Removed the comment about inferring the meaning of a resource of type skos:Concept, because it was misleading (move to intentional model, where properties of a concept *explain* the meaning of the concept, but do not determine it.  This allows for clearer modelling of concepts in multiple schemes).
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revision 1.32
date: 2004/12/17 13:23:26;  author: ajm65;  state: Exp;  lines: +10 -1
Changes to skos:Collection - The word 'meaningful' added to the definition; small change to the comment to make it clearer.
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revision 1.31
date: 2004/12/15 20:11:22;  author: ajm65;  state: Exp;  lines: +21 -5
Added skos:hiddenLabel
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revision 1.30
date: 2004/12/15 19:56:28;  author: ajm65;  state: Exp;  lines: +9 -4
Changed skos:inScheme - no longer a sub-prop of rdfs:isDefinedBy (because the latter is semantically more precise)
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revision 1.29
date: 2004/11/12 15:31:09;  author: ajm65;  state: Exp;  lines: +1 -1
added foaf namespace declaration (was missing)
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revision 1.28
date: 2004/11/11 13:12:58;  author: ajm65;  state: Exp;  lines: +1 -1
Single word change to definition of skos:subjectIndicator
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revision 1.27
date: 2004/11/11 13:07:35;  author: ajm65;  state: Exp;  lines: +30 -0
Spec sections added as subject indicators for all SKOS Core terms
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revision 1.26
date: 2004/11/11 12:52:17;  author: ajm65;  state: Exp;  lines: +4 -3
Added foaf:homepage prop to schema description
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revision 1.25
date: 2004/11/11 12:49:24;  author: ajm65;  state: Exp;  lines: +11 -13
Updated initial XML comment
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revision 1.24
date: 2004/11/11 11:18:57;  author: ajm65;  state: Exp;  lines: +24 -1
Added 'skos:subjectIndicator' property
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revision 1.23
date: 2004/10/22 11:55:42;  author: ajm65;  state: Exp;  lines: +2 -0
Added foaf:Document as domain/range for skos:subject/isSubjectOf
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revision 1.22
date: 2004/10/22 11:52:34;  author: ajm65;  state: Exp;  lines: +1 -1
fix bug in skos:subject
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revision 1.21
date: 2004/10/22 11:42:46;  author: ajm65;  state: Exp;  lines: +54 -3
Added skos:subject, skos:isSubjectOf, skos:primarySubject, skos:isPrimarySubjectOf
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revision 1.20
date: 2004/10/21 16:15:24;  author: ajm65;  state: Exp;  lines: +1 -1
fix bad link in example for editorialNote
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revision 1.19
date: 2004/10/21 14:22:26;  author: ajm65;  state: Exp;  lines: +93 -19
Added historyNote, editorialNote, changeNote.
Modified scopeNote, definition, example: removed domain statement, super-prop changed to publicNote.
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revision 1.18
date: 2004/10/21 14:05:26;  author: ajm65;  state: Exp;  lines: +27 -2
publicNote and privateNote added
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revision 1.17
date: 2004/10/20 17:10:45;  author: ajm65;  state: Exp;  lines: +62 -1
Collections vocabulary added (support for 'node labels' and 'guide terms')
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revision 1.16
date: 2004/10/20 16:36:14;  author: ajm65;  state: Exp;  lines: +24 -10
skos:externalID deprecated (use dc:identifier instead).
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revision 1.15
date: 2004/10/20 15:17:00;  author: ajm65;  state: Exp;  lines: +75 -0
Added a change note to all updated terms
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revision 1.14
date: 2004/10/20 15:09:45;  author: ajm65;  state: Exp;  lines: +17 -2
Updated dct:modified for all terms
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revision 1.13
date: 2004/10/20 15:07:48;  author: ajm65;  state: Exp;  lines: +10 -1
Added new comments
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revision 1.12
date: 2004/10/20 14:59:41;  author: ajm65;  state: Exp;  lines: +223 -193
Former comments on terms deprecated
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revision 1.11
date: 2004/10/20 14:49:37;  author: ajm65;  state: Exp;  lines: +18 -3
Added a skos:definition to all current terms
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revision 1.10
date: 2004/10/20 14:37:48;  author: ajm65;  state: Exp;  lines: +17 -1
Added examples to all current terms
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revision 1.9
date: 2004/10/20 14:31:32;  author: ajm65;  state: Exp;  lines: +25 -25
Added xml:lang to all rdfs:label statements
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revision 1.8
date: 2004/10/20 14:26:31;  author: ajm65;  state: Exp;  lines: +1 -1
Updated date modified for the schema
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revision 1.7
date: 2004/10/18 16:02:44;  author: ajm65;  state: Exp;  lines: +118 -67
The following terms deprecated and replaced by terms in the 'SKOS Extensions' vocabulary
 ...
'broaderGeneric'
'broaderInstantive'
'broaderPartitive'
'narrowerGeneric'
'narrowerInstantive'
'narrowerPartitive'
'relatedHasPart'
'relatedIsPartOf'
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revision 1.6
date: 2004/08/27 19:37:43;  author: ajm65;  state: Exp;  lines: +25 -1
Added dct:issued for all terms
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revision 1.5
date: 2004/08/19 13:05:05;  author: ajm65;  state: Exp;  lines: +29 -3
Deprecated class skos:TopConcept
Added property skos:hasTopConcept
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revision 1.4
date: 2004/08/03 17:31:13;  author: ajm65;  state: Exp;  lines: +1 -1
error 'ts' changed to 'vs' in namespace declaration
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revision 1.3
date: 2004/08/03 17:10:00;  author: ajm65;  state: Exp;  lines: +75 -5
Following changes:

- doctype changed to 'rdf:RDF'
- entity 'vs' added
- xmlns:vs added
- dct:modified date updated
- dc:title changed to 'SKOS Core RDF Vocabulary'
- dc:contributor added
- term status values added for all terms
- initial XML comment rewritten
- rdfs:isDefinedBy added for al terms
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revision 1.2
date: 2004/03/26 17:06:36;  author: danbri;  state: Exp;  lines: +208 -227
update from al
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revision 1.1
date: 2004/03/18 15:44:12;  author: danbri;  state: Exp;
swad-e thesaurus work in progress
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