Taxonomists vs. Ontologists? What’s the Difference?
I recently had the privilege of sitting in on Dan O’Conner’s Taxonomy Roundtable, and, while listening to my co-panelists on what exactly makes up a taxonomist, I made a realization: while there is a fair amount of overlap between being a taxonomist and being an ontologist, they are not the same thing. And this distinction should have some major implications for many organizations.
Defining the Taxonomist
A taxonomist uses a categorization scheme to determine how to classify a given term. Given that cats came up rather frequently in the discussion, it’s a useful way of understanding this. The term cat could in fact describe any number of things:
- that small, furry, four-legged mammal that wakes you up at 4am so you’ll feed her.
- a broader classification that covers any of the animals within the family Felidae, including lions, tigers, panthers, wild cats, leopards and similar animals.
- the shortened form of Caterpillar, the heavy machinery company.
- one of a number of costumed superheroes (most iconically, Catwoman) or villains (also Catwoman) in comic books who use the iconography of cats as their motif. Indeed, Catwoman represents a case study in taxonomy in her own right.
- a Unix/Linus based shell command that dumps the contents of a file to a given pipe (or the terminal).
- A musician formerly known as Cat Stevens, now Yusuf Islam.
and so forth.
The role of the taxonomist is to then take a particular entity or concept and determine into which particular bucket the term goes, along with providing a coherent definition of the term within the overall context of the categorization framework they are using.
In simplistic terms, a taxonomist defines and maintains the category buckets that a given article, image, or similar resource goes into. They provide clues about what that resource is about.
Ontologist: the Meta-Taxonomist
In 1980, fantasy author Lyndon Hardy wrote a novel called Master of the Five Magics, a book which had a profound impact upon me. While the trope is now common, at the time, his work was based upon a very novel conceit: there are magicians of various sorts who have very distinct and clear cut disciplines — Sorcerers, Thaumaturges, Enchanters, and so forth, each of which has their own distinct abilities and frameworks. The protagonist is a young man with clear magical potential, but no matter what he lays his hands to, the result is an unmitigated disaster.
It turns out that the reason for this is that the character is a meta-magician — he cannot master a given magical framework because his magic is in the creation of magical frameworks. He establishes the rules that establish the rules.
This is a remarkably good analogy for what an ontologist does. An ontologist is usually not involved directly in the classification of terms. Instead, he (or more likely she, it’s a profession that is slightly more dominated by women) identifies the relationships that exist between classes of terms, identifies the properties and terms used for definition and sets the underlying model by which the classification system is built. In this regard the position if more like an architect than it is a developer.
As an example, many taxonomists use a classification scheme (written by an ontologist) called SKOS — the Simple Knowledge Organization System. This system lends itself well to hierarchical organization, such as a Linnaean taxonomy (the early taxonomy system first created by swedish biologist Carl Linnaeus in 1735) or its descendents. It has the relationships “broader term” and “narrower term” and works by assuming that the closer you get to the root, the broader the category.
SKOS does contain a few other relational terms, including a general “related term”, as well as equivalency terms of increasing narrowness that identify whether a given term is (more or less) the same as another. The problem with such systems is that they are almost completely based on subclassing (domestic cats are subclasses of felidae, as an example), but as such they don’t handle other kinds of relationships (such as ownership relationships, or familial relationships — a given housecat is not a subclass of its mother).
The role of the ontologist, then, is to identify the specific kinds of relationships that may exist for a given taxonomy, and to establish models telling how various things within a domain relate to one another. They determine the rules of the model.
Partners in Crime (and Classification)
Part of the reason that there seems to be so much overlap between taxonomists and ontologists is that taxonomists are highly intelligent people who think about relationships, and so it’s not uncommon for taxonomists to become ontologists. On the other hand, ontologists may also common from the data modeling side of things — when a person designs a database or creates an entity relationship diagram, they are in fact engaging in basic ontology.
The ontologist will likely be working one on one with your database designers, while talking to (or even managing) the taxonomists. The ontologist determines the need for an Address Type dropdown to exist on a user interface, the taxonomist determines what alternatives that drop-down displays.
So, both professions are valuable in an organization. Your ontologist builds the models that identify the things of importance in your enterprise (and how they relate), the taxonomist then determines how those entities are classified based upon the ontologists model.
Kurt Cagle is the founder and Chief Ontologist for Semantical, LLC, a smart data company.
