Defining Taxonomy & Classification

Awhile back, in June 2004, the Delphi Group published a whitepaper entitled "Information Intelligence: Intelligent Classification and the Enterprise Taxonomy Practice". The document includes some excellent definitions which I've excerpted (with edits) below:

Taxonomy -- is a hierarchical (or polyhierarchical) listing of topics or subject categories. It need not include a definition of topics, but only the hierarchical relationship of topics to one another. There are no standard approaches to taxonomy construction. A taxonomy is often used to provide a structured navigational path through a content collection.

Thesaurus -- is a network of words and word meanings and relationships used to put conceptual definitions into context. It defines a lexicon that describes relationships between words. Thesaurus construction is defined by ANSI standard Z39.19. A thesaurus is often used to enhance the intelligence of a taxonomy by providing insight into word meanings and relationships.

Ontology -- is a network of relationships that are self-describing and used to track how items or words relate to one another. For example, a "lives at" link or "works for" link in an ontology would be used to track these types of relationships and their corresponding values for listed individuals.

Classification -- is the process of analyzing content and determining where in a taxonomy it belongs. For example, the assigning of a Dewey decimal code to a book, based on the mapping of its content into the Dewey decimal system, is a form of classification.