Taxonomy

A taxonomy is a controlled set of terms arranged in a hierarchy of broader and narrower categories. Each term has one preferred label, and every item is classified by one or more terms. Taxonomies are one kind of Controlled vocabulary.

What a taxonomy does

• Groups content so that people can browse it through Navigation systems
• Keeps classification consistent across authors, so filters and search results are reliable
• Gives Metadata fields a fixed set of allowed values

Hierarchy is not the only relation

Strict taxonomies express only "is a kind of" or "is part of". When content needs to be described along several independent dimensions — product, audience, task, lifecycle phase — a single tree forces awkward choices. Faceted classification solves this by using several small taxonomies side by side.

When relations beyond hierarchy matter ("is required by", "replaces", "applies to"), a taxonomy grows into an Ontology.

Designing one

Start from users' vocabulary (Card sorting, search logs) and from the content itself; keep categories mutually exclusive at each level where possible; and document scope notes so authors classify the same way. SKOS, the W3C standard for publishing taxonomies and thesauri, models this with skos:broader and skos:narrower.

See also the site's information architecture and ontology glossary.