Reference Glossary
Thesaurus (metadata)
A controlled vocabulary defining hierarchical (broader/narrower) and associative relationships between terms — not just equivalence — used to guide consistent indexing and searching.
Why it matters in a DAM
A properly built thesaurus lets a search for 'vehicle' also surface assets indexed only under narrower terms like 'truck' or 'sedan', because the broader/narrower relationship is explicit in the structure — something a flat keyword list or a synonym ring can't do. ANSI/NISO Z39.19 is the standard that specifies exactly how these relationships (broader term, narrower term, related term, use/used-for) should be built and documented for this purpose.
A worked example
Common mistake
Teams build a folder hierarchy or nested category tree in the DAM and call it a thesaurus, but a folder structure only encodes one relationship — containment — with no equivalence or associative links, so it can't drive the 'search broader term, get narrower results too' behaviour a real thesaurus supports.
A thesaurus, in the metadata sense, is a more structured relative of a synonym ring. Where a synonym ring says a set of terms are equivalent, a thesaurus captures multiple kinds of relationship at once: broader term, narrower term, related term, and preferred term versus non-preferred (use/used-for). That extra structure is what lets a search engine do more than exact matching or flat equivalence.
The practical payoff is hierarchical retrieval. If ‘Vehicle’ is defined as the broader term for ‘Truck’, ‘Sedan’, and ‘Motorcycle’, a search for ‘Vehicle’ can be configured to also return assets indexed only under the narrower terms — without anyone having tagged those assets ‘Vehicle’ directly. That saves indexers from having to apply every level of a hierarchy manually to every asset.
ANSI/NISO Z39.19 is the reference standard for how to build this correctly — it defines the relationship types, how to pick a preferred term among near-synonyms, and how to document the whole structure so it stays maintainable. That standard is also why a plain folder tree in a DAM isn’t a thesaurus, even though it looks hierarchical: folders encode containment (this asset lives inside this folder) rather than the semantic broader/narrower and associative relationships a thesaurus is built to express, so a folder structure can’t support the same kind of expanded retrieval.
Frequently asked
How does a metadata thesaurus differ from a synonym ring?
A synonym ring only captures equivalence between terms; a thesaurus captures multiple relationship types at once — broader term, narrower term, related term, and preferred versus non-preferred (use/used-for) — giving it more structure to work with.
What does the broader/narrower relationship in a thesaurus let a search engine do?
If 'Vehicle' is defined as the broader term for 'Truck,' 'Sedan,' and 'Motorcycle,' a search for 'Vehicle' can be configured to also return assets indexed only under the narrower terms, without anyone tagging those assets 'Vehicle' directly.
What standard specifies how a metadata thesaurus should be built?
ANSI/NISO Z39.19 defines the relationship types, how to pick a preferred term among near-synonyms, and how to document the structure so it stays maintainable.
Is a folder hierarchy in a DAM the same as a thesaurus?
No — a folder structure only encodes containment, meaning this asset lives inside this folder, not the semantic broader/narrower and associative relationships a thesaurus expresses, so it can't drive the 'search broader term, get narrower results too' behaviour a real thesaurus supports.
Why does a thesaurus save indexers work compared to manual hierarchy tagging?
Because a search for a broader term can automatically surface assets tagged only with narrower terms, indexers don't have to apply every level of a hierarchy manually to every single asset.
What's an example of the 'use/used-for' relationship in a thesaurus?
'Automobile → USE Car' — directing a non-preferred term to the preferred term the vocabulary actually indexes under.
Sources
- ANSI/NISO Z39.19 specifies how to formulate descriptors and establish standardized relationships among terms — broader, narrower, related, and use/used-for — for controlled vocabularies including thesauri. checked 2026-08-07 — NISO — ANSI/NISO Z39.19-2005 (R2010)