Thesaurus

Central question

How are words connected for retrieval?

Reader promise

The reader will be able to read a thesaurus entry and say exactly what each relationship permits a search system to do, and will stop treating "related term" as a weak form of "same thing."

Required development

1. Explain preferred and alternative terms. A thesaurus chooses one term to stand for a concept and records the others as entry points that lead to it. Show how this differs from a dictionary and a list of synonyms, and why the choice of preferred term is a governance decision rather than a linguistic fact.
2. Distinguish broader, narrower, and associative relationships. Define each as ISO 25964 does. Show, with one synthetic example from nuclear medicine terminology, that the broader relationship supports query expansion downward, that the associative relationship supports suggestion but not expansion, and that neither asserts equivalence.
3. Compare ordinary and controlled thesauri. Contrast Roget's thesaurus, which groups words by idea for a writer, with a retrieval thesaurus built to a standard for an indexer and a searcher. Explain what "controlled" adds: one preferred term per concept, scope notes, and a maintenance process.
4. Connect the thesaurus to SKOS, the W3C vocabulary for publishing thesauri on the web, and state what it does and does not formalize.

Evidence and review

Evidence to obtain: ISO 25964-1 for the normative definitions of the relationship types and of a preferred term; the SKOS Reference for the properties broader, narrower, and related and the consequences SKOS attaches to each; Roget's original preface for the design intent of a writer's thesaurus; and one published biomedical thesaurus or indexing vocabulary, cited to a named release, as a documented case.

Review concern: readers and systems routinely treat an associative link as a loose equivalence and merge the two concepts. The manuscript must demonstrate a case where two terms are correctly related and plainly not equivalent, and must state that no thesaurus relationship licenses substitution of one term for another.

Planned internal links

Thesaurus, Synonym, Controlled vocabulary, Controlled vocabularies for governance and identifiers, and Taxonomy for the hierarchy that a broader relationship resembles but does not reproduce. Link at the point of use.

Review requirements

Source check against the ISO standard and the SKOS Reference. Domain review by an information scientist or medical librarian. Editorial check that the synthetic example uses no real terminology codes.