1. Use Case Diagrams

2. [UC01] Log in

ID	UC01
Name	Log in
Brief Description	The user logs in the system.
Actor	Consumer user

Main Flow
1.	This use case starts when the user accesses a protected page. The system displays a login form.
2.	The user enters ID and password. The system authenticate the user, and displays the protected page requested. The use case ends.

Alternative Flow 1    Starts after Main Flow - step 1
1.	The user enters invalid ID or password. The system displays an error message. The use case ends.