Is it necessary to include the login for every use

问题:

iam going to design a system that has a login facility. After login the logged user can do several things so is it needs to include login usecase by that several usecases.

回答1:

In most cases, it will only clutter up your diagrams. Login is neither complex nor does it give you much added value as a use case. In your textual document that includes the use cases with description, include as a prerequisite a list of features that require a successful login. Easier to track and to test.