Yes. We use categories to describe a system. We categorize an engine into a the ignition system, cooling system, air intake system, ect.. We describe node.js by

Yes. We use categories to describe a system. We categorize an engine into a the ignition system, cooling system, air intake system, ect.. We describe node.js by its categories -- errors, file system, streams, ect.. Systems are cyclic which means humans can pretty well make assumptions of a future state of a system by the current and past state of that system. If we want to know a future state, we need to first describe the system. I really like Robert Pirsig's idea of an analytical knife from "Zen and the Art of Motorcycle Maintenance" to cut up systems into categories or category trees, there isn't a one way to do it but rather many ways to describe a system in categories that are more and less useful.