We were working with a client recently who wanted to incorporate their existing taxonomies into their newly forming enterprise ontology. It was, as they say, a “teachable moment.” Not all taxonomies are created equal. At least not with regard to their being able to be integrated into an ontology. Most people start a taxonomy project with a slide in their power point deck showing the Linnean taxonomy. Some variation on this blogimage And then proceed to build indented lists and call them taxonomies. But what Carl Linnaeus knew, and we often conveniently forget, is that this taxonomy is special, in that all members of any lower order are also members of all their higher orders. That is, all dogs are carnivores, all carnivores are mammals, all mammals vertebrates, etc. This is called a formal taxonomy. The easy test for a formal taxonomy is to just ask “isa?” or more fully “is a instance of the lower level category necessarily a type of the higher level category?” at each level and if the answer is yes, then it’s a formal taxonomy. But most taxonomies are not formal. Many, especially those being developed in “Information Architecture” are “navigational” that is the taxonomy exists to help a human web visitor find what they are looking for. For instance the Google merchant taxonomy has a set of categories as follows: Baby & Toddler Nursing & Feeding Baby Bottle Nipples This may be useful to find things, but if we ask “are all members of Baby Bottle Nipple” necessarily a type of “Nursing &Feeding” is either “Nursing & Feeding” or “Baby Bottle Nipples” a type of “Baby & Toddler?” Clearly no. If we naively import informal taxonomies into our ontologies, we may get into trouble. More in a future episode.