UML contracted user case contains system borders?

Question

Does contracted user case contain system borders? I mean: does it contain something like: machine doing biscuits, or just selling.

Answer 1

• According to UML standard, every use case element MUST have at least one association with an actor element.
• So, if you want to show something as border classes, i.e., elements that are connected to user and elements that are not connected to user, it is impossible. EVERY use case shown in UC diagram must be connected to user.
• The UC diagram is not for showing inner, invisible for user behaviours. Its purpose is to define the subject _{^{(according to UML standard, the product you are working at)}} by defining all its external behaviours.
• A system on UC diagram is shown as a rectangle. Its borders contain the use cases that belong to the system. The same for subsystems, components and packages on the UC diagram.
• So, a machine whose functionalities only support other machines, but never works with Actor (human or external system), is NOT a subsystem in UC diagram terms. Its functionality is not a use case. If you'll try to show it somehow here, you'll get a very bad and unreadable UC diagram. Show it on component and deployment diagrams.

Answer 2

You have to depict the relevant use cases for each actor. So what are your actor(s) and does it make sense to associate them to "machine doing biscuit" or "selling" use cases?