The Simple Knowledge Organisation Systems (SKOS) http://www.w3.org/2004/02/skos/ is an area of work developing specifications and standards to support the use of knowledge organisation systems (KOS) such as thesauri, classification schemes. This format is used by GeoNetwork to store thesaurus information.

A concept is defined by an identifier, a prefered label, a definition and links with other concepts. Labels and definitions could be stored in multiple languages (using the xml:lang attributes). Three type of links between concepts have been defined in the SKOS format:

For example, a concept ”ABLETTE” could be defined as follow with a label in french and english, linked to broader concept:

<skos:Concept rdf:about="http://www.oieau.org/concept#c4fc54576dc00227b82a709287ac3681">
    <skos:prefLabel xml:lang="fr">ABLETTE</skos:prefLabel> 
    <skos:prefLabel xml:lang="en">BLEAK</skos:prefLabel>
    <skos:broader rdf:resource="http://www.oieau.org/concept#9f25ece36d04776e09492c66627cccb9"/> 
</skos:Concept>

GeoNetwork support multilingual thesaurus (e.g. Agrovoc). Search and edition are made based on current user interface language (i.e. if the interface is in english, when editing metadata, GeoNetwork will only search for concept in english).