Which is abstract-er, Tuesday or Situation?

March 10, 2010

Weirdly enough, this isn’t a rhetorical question. (That it’s not is one of the many things I love about my job.)

Lately I’ve been evaluating Proton, an upper ontology developed by SEKT, which is an EU initiative. Most of the ontologies I evaluate aren’t written by actual ontologists, which leads to a certain amount of ranting and despair on my part. Proton has been developed by a number of skilled ontologists and logicians, and it’s a pleasure to spend time with a well-thought-out model. Of course, modeling is an art, and I don’t agree with every modeling decision in Proton — but that’s okay, because my disagreements give me a lot of food for thought.

One idea that’s given me pause is whether or not notions of time and number are more abstract than other concepts in an ontology. In Proton’s model, classes generally descend from the Entity class, with the exception of a few system classes. Entity has three direct subclasses, Abstract, Happening and Object. The full hierarchy looks like this:
Proton top-level entities

Thinking about it, I can’t come up with a single reason why the concept of time is more abstract than any other concept represented in an ontology. I understand that it’s modeling an abstraction — there’s no concrete thing in the world called Tuesday; it’s a concept in our calendar system. But there’s also not a concrete thing in the world represented by the class “Boston Marathon” or “US Currency” or “World Leader”. There are real instances of all those classes, but Tuesday March 9th is a real instance of the concept of Tuesday. So, is there a difference? 10 points to anyone who can explain it to me.

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