Extension Cases

Not all plans go according to… well… plan. In the description above, everything went exactly as it should. However, there will be times when something goes awry. These cases are called extensions. Extensions follow up on certain steps in the description.

An extension starts with the number of the line that has an alternative followed by a, b, c, etc., depending on number of alternate cases. Each extension then describes the alternate flow of events.

Extensions
1a. No items in shopping cart
 1. System informs Customer to add items to cart before continuing

1b. Some/All items in shopping cart no longer available
 1. System removes items no longer available
 2. System notifes Customer that items have been removed

2a. Customer is a registered user
 1. System prefills saved shipping information
 2. Customer may change shipping information

5a. Authorisation fails (credit card declined)
 1. System notifies Customer
 2. Customer may reenter credit card information or cancel

5b. Authorisation fails (bank not responding) 
 1. System notifies Customer and requests to try again later

This describes the extension cases for the use case and description in of the use case diagram above

Use Case: View Individual Marks
Input: 
Output: 
1. Lecturer selects student
2. System displays relevant student’s current marks

Use Case: Update Individual Marks
Input: 
Output: 
1. Lecturer selects student
2. System displays relevant student’s current marks
3. Lecturer changes one or more marks
4. System validates marks
5. System stores marks

Extensions
4a. Invalid mark entered
1. System notifies Lecturer of invalid mark
2. Lecturer can fix mark or cancel