It is a set of representations defined by characteristics.
Distinguishing two representations from each other (a four legged stool from a dog) creates at least two categories.
Further distinguishing characteristics can form further categories and represented in an ontology, most likely loosely hierarchical in presentation even if cross connected.
The error to be aware of would be mistaking the model for the thing.
https://en.wikipedia.org/wiki/Action_theory_(philosophy) I suppose.