Introduction

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What is SKOS Core ?

SKOS Core is an RDF vocabulary for describing ...

thesauri,
terminologies,
glossaries,
subject heading schemes,
other types of controlled vocabulary.

It can also be used for ...

taxonomies,
classification schemes,
web directories,
category schemes.

Thesauri, taxonomies, classification schemes etc. are collectively known as 'knowledge organisation systems' or 'KOS' ... which is the root of the name 'SKOS'.

Why Publish in RDF?

If you publish your KOS on the web in a human-readable form, other people will be able to use it for manual tasks. If you publish your KOS on the web in a machine-readable form, other people will be able to use within their computer programs and applications.

Publishing structured information on the web in a machine-readable form is the fundamental principle of the 'semantic web'.

The Resource Description Framework (RDF) is the W3C recommended standard for publishing structured information on the web.

What is an RDF Vocabulary?

An RDF vocabulary is a set of 'classes' and 'properties' that allow you create an 'RDF description' of something. For example, the Dublin Core element set is an RDF vocabulary for describing document metadata. The Friend of a Friend (FOAF) vocabulary is an RDF vocabulary for describing people and social networks.

This guide will introduce you to creating RDF descriptions of knowledge organisation systems, using the SKOS Core vocabulary.

Do I Need to Know RDF to Read This Guide?

To use the 'quick start' section of this guide, you do not need to understand the abstract model underlying RDF, but it helps.

To use the 'advanced features' section of this guide, you do need at least a basic understanding of the graph data model, and the use of RDF schema to declare new classes and properties.

The RDF Primer [ref] is a good place to start with RDF, links to other tutorials can be found on DBRP [ref].

RDF and XML?

RDF has an abstract model [ref], which is based on the 'directed labelled graph'.

Because RDF has an abstract model, it can be serialised (i.e. written down) in several alternative ways.

There are currently three mandated and commonly used syntaxes for serialising RDF data:

RDF/XML,
Notation 3 (N3),
N-Triples.

The examples in this guide are all written in the RDF/XML syntax, for consistency. But bear in mind that SKOS Core is NOT an XML syntax for knowledge organisation systems - it is an RDF vocabulary for describing knowledge organisation systems ... that can of course be serialised using any of the mandated RDF syntaxes.

Understanding the RDF statements that a snippet of RDF/XML or N3 represents is the key to unlocking the power of RDF.

End of Intro

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SKOS Core and OWL?

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The Web Ontology Language (OWL) is the W3C recommended standard for publishing ontologies on the web. Ontologies are a type of knowledge organisation system that logic structures - allows inference ...

Many used KOS are not structured according to logical formalisms. The trade off here is flexibility for decidability - i.e. you have more flexibility in so far as what you can say, but less potential in so far as the inference you can logically compute.

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AJM first draft>

SKOS Core is an RDF vocabulary for describing language-oriented knowledge organisation systems (KOS) such as thesauri. glossaries, terminologies and other types of controlled vocabulary. It is also well suited to hierarchically organised KOS such as taxonomies and classification schemes, where the hierarchy of categories or concepts is not necessarily a logically consistent class subsumption hierarchy. In other words, you can use SKOS Core to describe a set of concepts, categories or subjects of interest, and organise them into a hierarchy, without needing to know anything about logic.

SKOS Core is an RDF vocabulary, which means it gives you a set of basic building blocks for creating an RDF description of your thesaurus, glossary, blog category scheme etc. By publishing an RDF description of your thesaurus on the web, you become a part of the semantic web, which means that not only can other people access and re-use the content of your thesaurus, but so can other computer programs and applications. .

This guide tries to assume the reader knows next to nothing about the Resource Description Framework (RDF) or the Semantic Web. A selection of resources introducing and explaining these ideas is included in the references, if you would like to explore them further.

All the examples in this guide use the RDF/XML serialisation of RDF. It is worth noting that RDF can be written down (serialised) in a number of different formats - see the references for more information.

This guide is a complement to the SKOS Core Vocabulary Specification. The Specification provides and overview and reference guide to the SKOS Core vocabulary. This document tries to explain how to use it.

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