2. Structure

More than any other characteristic, it is its relational structure that distinguishes thesauri from other document languages used for representation and retrieval, such as classification schemes and keyword lists. In a thesaurus, relationships between concepts are paradigmatic in nature, i.e. they are permanent, necessary and always true in the semantic environment described. Paradigmatic relationships are the opposite of syntagmatic relationships. The syntagmatic relationship recreates the context in which a concept is used, by juxtaposing concepts that have no permanent relationship with each other at the time of indexing or search strategy development.