A taxonomy is a classification scheme. The oldest form of taxonomy, and the one that is most likely to be familiar to you if you are a life scientist, is the Linnean classification of organisms. Typically, taxonomies are hierarchical: each ‘child’ term (more specific term) has one ‘parent’ term (more generic term), and a parent term can have one or many children. This is the case in the Linnean taxonomy (Figure 7): we start off with living organism, move to domain, then kingdom, then phylum, class, order, family, genus and finally species.

Taxonomies do not have to be hierarchies; they may also be networks, in which a child term can have one or many parents. The main advantage of using a taxonomy over a non-hierarchical list is that you can find everything annotated as a sub-category of the search term.

Figure 7 The Linnean classification of organisms – possibly the archetypal example of a taxonomy.