| The use case model provides a complete, black-box, outside-in view of system functionality | |
| A use case is a procedure by which an actor may use the system | |
| A good use case is largely a sequence of interactions across the system boundary between the actor(s) and the system written in easy to understand natural language | |
| An actor is always outside the system being defined | |
| The actor that starts the use case is the primary actor for that use case | |
| An actor is a role defined by the set of use cases with which it is associated | |
| Time is external to the system and so can be an actor which starts a use case 'automatically' |