A thesaurus is a networked collection of controlled vocabulary terms. This means that a thesaurus uses associative relationships in addition to parent-child relationships. The expressiveness of the associative relationships in a thesaurus vary and can be as simple as “related to term” as in term A is related to term B.

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A thesaurus has two kinds of links: broader/narrower term, which is much like the generalization/specialization link, but may include a variety of others (just like a taxonomy). In fact, the broader/narrower links of a thesaurus is not really different from a taxonomy, as described above. A thesaurus has another kind of link, which typically will not be a hierarchical relation, although it could be. This link may not have any explicit meaning at all, other than that there is some relationship between the two terms.