SKOS (Simple Knowledge Organization System)

SKOS (Simple Knowledge Organization System) is a W3C recommendation 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 and use of such vocabularies as linked data.

Overview

SKOS provides a model for expressing the basic structure and content of concept schemes such as thesauri, classification schemes, subject heading lists, taxonomies, folksonomies, and other similar types of controlled vocabulary. As an application of the Resource Description Framework (RDF), SKOS allows concepts to be composed and published on the World Wide Web, linked with data on the Web and integrated into other concept schemes.

Core Features

• Concepts and Concept Schemes: SKOS is based around concepts, which can be identified with URIs, labeled with lexical strings, assigned notations, documented with notes, linked to other concepts, and organized into informal hierarchies and association networks.

• Semantic Relationships: SKOS provides properties for representing hierarchical (broader/narrower) and associative relations between concepts.

• Multilingual Labels: SKOS allows concepts to be labeled in multiple languages, with properties for preferred, alternative, and hidden labels.

• Concept Collections: Groups of concepts can be defined and labeled, with a loose notion of membership.

Common Use Cases

SKOS is widely used in:

• Digital libraries for subject indexing
• Knowledge management systems
• Semantic Web applications
• Linked Data initiatives
• Vocabulary alignment and mapping projects

Relationship to Other Standards

SKOS complements other semantic web standards like OWL (Web Ontology Language) and provides a simpler approach for many knowledge organization tasks. It bridges the gap between formal knowledge representation languages like OWL and the chaotic, informal world of unstructured information.

Usage in Knowledge Graphs

SKOS is often used within knowledge graphs to organize concepts and provide a controlled vocabulary layer. Many domain-specific ontologies import SKOS concepts to support labeling and organizing their terms. It serves as a foundational vocabulary for semantic interoperability across different knowledge systems.

More Information

• SKOS Home Page
• SKOS Primer
• SKOS Reference