Taxonomies have many appearances: they can be simple navigation lists on a website, tree structures, structured schematic representations, etc. Ontologies define relations between concepts and can be seen as a more advanced kind of thesauri. Librarians sometimes have mixed feelings regarding both: they feel that their expertise is not valued. Although taxonomies and ontologies have many applications in knowledge management, they may be used as instruments to index documents. The full power of ontologies will be realised in the Semantic Web.
Classifications make strange bedfellows.
(David Weinberger [1: 90])