use case diagrams - need we add validations?

Question

Say I am building a use case diagram, and there is a use case that asks for some user input (a phone number).

The requirements ask that the phone number be valid (there is an API that tests for this, in this hypothetical).

Must "validate phone number" appear in the diagram? Can it? Should it?

My impression is that it does not have to, because it does not originate from a user action, but that is is permissible

Answer 1

I don't think it would appear in a use case diagram.

Although a use case is a series of steps in an interaction between a user and the system, the thing that appears in a use case diagram is really the title of a use case and not the complete use case itself. You could include a "validate phone number" as a use case that is included in other use cases on your diagram, but I would think that this would only add clutter.