What is the Difference between Taxonomy and Ontology? It is a Matter of Complexity

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Coming from a product information background, I didn’t have a firm grasp on ontology when I first arrived at Earley Information Science (EIS). I have a thorough understanding of taxonomy, but this next level concept was something I had not encountered. However, I was eager to learn, and I reached out to my colleagues to help me better understand ontology. The response was overwhelming. People readily shared their ideas about ontology, each providing a unique and valuable perspective.

Our CEO, Seth Earley, defines ontology as “a collection of various taxonomies that can be used to describe a domain of knowledge along with the relationships among them.” Seth Maislin, one of our principal consultants, says, “Ontology deals with the metadata of associative relationships.” From what I can derive from these definitions, ontology specializes in relationships and the intricacies therein. Taxonomy identifies relationships between items and categories, but lacks the complexity that ontology provides.

Being a Cubs fan, I appreciated the wonderful analogy that Seth Maislin provided:

“Ontology is interesting because we can start applying metadata to the relationship itself. For example, we don’t just say Cubs and Wrigley are related. We say that Cubs play baseball at Wrigley. And we can note that baseball season doesn’t last all year – which means the Cubs/Wrigley relationship could be seasonal. This is inference, and is the coolest feature of ontology.”

He expands on this by adding: “We can also connect relationships with other terms, such that only within the context of baseball would Cubs and Wrigley be related. Thus the relationship is not absolute.” This example really drove it home for me. The different ways a relationship can be described and how that relationship may have aspects, like seasonality, really illustrates the complexity of an ontology. It makes the relationship active or inactive, which then triggers other relationships. Whereas a taxonomy is a defined, static entity, an ontology is dynamic. 

In the world of Product Information Management (PIM), we see relationships such as accessories in taxonomy, but there is not a way to further that relationship. It’s either linked or it is not. This had been my understanding of relationships until I began exploring ontologies. Now I can see that by going a step further, ontology can provide added layers to that relationship and take it outside of PIM.

Ontology looks at a much larger universe. “There can be all kinds of taxonomies in an ontology,” says Dino Eliopulos, Managing Director at EIS, “but the real difference is that an ontology attempts to describe and capture an entire subject area, with all of its complexity, whereas a taxonomy tries to simplify a complex collection of seemingly unrelated items into a linear, organization.”

As a taxonomist, I am always looking for efficiency, simplicity, and ease of use, so I can see why ontology has eluded me. It is complex, minute and detailed in a way that can be daunting, but extremely impressive and necessary for specific needs of understanding and using data.

I had several more replies from others in the company that were just as useful and helped cement these concepts in my slightly overwhelmed head. I decided as a next step I would download a free ontology tool and try to create my own ontology. I found a tool called OWL and created an ontology of Star Wars information. (See the diagram below.) A set of relationships that definitely shows the need for relationship metadata is with Han Solo, Leia Organa Solo, and their children. For example, Leia is the mother to Ben Solo (aka Kylo Ren) in the movies and she is also mother to Jacen, Jaina and Anakin Solo in the book series.

What is the difference between taxonomy and ontology

The Parent Child relationship is an inverse relationship that can have the additional metadata for Mother as the Parent for Leia and Jaina. Further metadata can be added to indicate that the relationship is in the book series but not in the movies. Additional information as to where and when the child was born can be added as well.

Relationships can be created for different kinds of objects. Leia lived on the planet Alderaan, which can be another object. Metadata for that relationship, such as date range, can be added. Leia was portrayed by the actress Carrie Fisher, another relationship but in a separate dimension of the ontology.  We can see different taxonomy focal points for characters, actors, and locations being used within this ontology, among many others, to create many different kinds of relationships and the relationship metadata.

Exploring the meaning of ontology was a great exercise and drove the concept home of ontology vs taxonomy. I highly recommend giving it a try if you want to further your knowledge. The knowledge management that goes into an ontology can be very complex, but exciting to produce.

 

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