Permissions and Capabilities

Users are a central concept to any software system. Even single-user systems have users, maybe even multiple users, just never at the same time. Looking at the user concept through the eyes of a developer, however, roles are a better concept. The reason is simple — roles are abstract where a user is an instance of one role or another. This is how we think about most other things in the system, so why not the actors that we're interacting with too? We're not interested in the user who is currently interacting with the system, because that's not how the UI components are designed. They're designed around roles. The role describes for the developer, what this user instance is capable of doing. Roles are about permissions and the underlying capabilities of system. The two are interrelated, but when separated, as they so often are, cause major headaches in the code.