Compare methods

	Controlled Vocabulary Indexing	Thesaurus Construction
Field	Library Information Science	Library Information Science
Family	Process / pipeline	Process / pipeline
Year of origin	2005	2000
Originator	ANSI/NISO Z39.19; Elaine Svenonius	Jean Aitchison, Alan Gilchrist & David Bawden; ANSI/NISO Z39.19
Type	Indexing pipeline using a controlled vocabulary	Standards-based pipeline for building an information-retrieval thesaurus
Seminal source	NISO. (2005). ANSI/NISO Z39.19-2005 (R2010): Guidelines for the Construction, Format, and Management of Monolingual Controlled Vocabularies. Baltimore: NISO.	Aitchison, J., Gilchrist, A., & Bawden, D. (2000). Thesaurus Construction and Use: A Practical Manual (4th ed.). London: Aslib/IMI. ISBN: 9780851424460
Aliases	Subject Indexing, Controlled Indexing, Assigned Indexing, Vocabulary-Controlled Subject Indexing	Thesaurus Building, Thesaurus Development, Controlled Vocabulary Thesaurus Design, Information Retrieval Thesaurus Construction
Related	3	3
Summary	Controlled vocabulary indexing is the process of representing what a document is about by assigning preferred terms drawn from an established controlled vocabulary or thesaurus, rather than from the document's own free-text words. ANSI/NISO Z39.19 codifies the practice: the indexer first performs conceptual analysis to determine a document's aboutness, then translates each concept into the vocabulary's preferred term, choosing how many concepts to capture (exhaustivity) and how finely to express each (specificity). Elaine Svenonius's account of subject languages explains why this controlled translation matters — it eliminates the synonymy and homonymy of natural language so that one concept is always indexed under one term. Done consistently, controlled vocabulary indexing gives a collection reliable, predictable subject access that free-text search alone cannot guarantee.	Thesaurus construction is the systematic building of a controlled vocabulary in which preferred terms are linked by a standardized set of relationships — equivalence, hierarchy, and association — to support consistent indexing and effective retrieval. The definitive practical methodology was set out by Jean Aitchison, Alan Gilchrist, and David Bawden in their manual Thesaurus Construction and Use, and the controlling standard in the United States is ANSI/NISO Z39.19, with ISO 25964 as its international counterpart. A thesaurus collects the terms a domain uses, resolves synonyms and homographs so each concept has one preferred label, and then wires the preferred terms together with USE/UF, BT/NT, and RT relationships plus scope notes. The result is a structured map of a subject's concepts that indexers and searchers share, reducing the mismatch between the words authors, indexers, and users choose.