CS 160: Software Engineering

Sections 1 and 2

Spring Semester 2008

Department of Computer Science
San Jose State University
Instructor: Prof. Ron Mak

Assignment: Use cases
Solution Example

There is, of course, no single solution. Some points:

• The goal statement should be clear and succinct.
• The primary sequence of steps should in fact accomplish the goal statement.
• Actors are not necessarily people.
• Don’t forget actors such as the bank, the product database, or the employee database if they’re involved in the sequences.
• The trigger is an action by an actor that kicks off the primary sequence.
• The trigger should not be included in the primary sequence. If it is, it should be the first action of the sequence.
• Do not include GUI details in the primary or alternate sequences.
• Performance criteria are easy nonfunctional requirements to include.
• Don’t ignore the glossary. Its entries will help later with object design.

1. Use Case Diagram

2. Get Item Price

Project Name:	Assignment 1: Use Cases
Use Case Name:	Get Item Price
Authors:	R. Mak

1. Goal

Get the price of a purchase item.

2. Summary

The clerk gets the price of an item that the customer wants to purchase by scanning the item at the supermarket checkout station.

3. Actors

Actor 1: Clerk (primary)

Actor 2: Customer

Actor 3: Product database

4. Preconditions

1. The clerk has successfully logged onto the supermarket checkout station (use case Login Clerk).

2. The customer has brought an item to purchase to the checkout station.

3. The item has a barcode.

5. Trigger

The clerk scans the purchase item at the checkout station.

6. Primary Sequence
Step	Action
1	The scanner reads the item’s product code from the barcode.
2	The scanner sends the product code to the product database.
3	The product database looks up the product and returns information such as the name of the product and its price.
4	The checkout station displays the product name and its price.
5	The checkout station adds the item price to the customer’s running total.

7. Alternate Sequences
Step	Action: Checkout station scanner fails to read product code.
1	The clerk enters the product code manually.
2	The clerk submits the just-entered product code.
Step	Action: The product database fails to find the product information.
1	The clerk calls for help.

8. Postconditions

1. The purchase item description and price are displayed and the price is added to the customer’s running total.

2. The product database records a sale.

--- OR ---

3. The customer cannot purchase the item and the running total and product database are not changed.

9. Nonfunctional Requirements

1. A “boop” is audible each time an item is scanned.

2. Product information is retrieved within 5 seconds.

10. Glossary

clerk: the actor who obtains the price of a purchase item by scanning it

customer: the actor who wants to purchase the item

product database: the actor that retrieves product information based on the product code

3. Pay Debit Card (with cash back)

Project Name:	Assignment 1: Use Cases
Use Case Name:	Pay Debit Card (with cash back)
Authors:	R. Mak

1. Goal

Pay by debit card with cash back.

2. Summary

The customer pays for the purchases with a bank debit card and asks for cash back.

3. Actors

Actor 1: Customer (primary)

Actor 2: Clerk

Actor 3: Bank

4. Preconditions

1. The total price of all the purchases is displayed.

2. The customer has successfully swiped the bank debit card (use case Swipe Debit Card).

5. Trigger

The customer requests cash back.

6. Primary Sequence
Step	Action
1	The customer enters the desired amount of cash back at the checkout station keypad.
2	The station adds the cash back amount to the customer’s total.
3	The station notifies the customer’s bank of the total amount.
4	The bank deducts the total amount form the customer’s bank account.
5	The checkout station displays the cash back amount.
6	The clerk gives the customer the cash back amount in cash.
7	The checkout station prints the receipt.
8	The clerk hands the receipt to the customer.
9	The customer leaves with the cash and the purchases.

7. Alternate Sequences
Step	Action: Bank account insufficient.
1	The checkout station keypad displays “Insufficient funds in account”.
2	The customer enters a lesser amount for cash back and/or “unpurchases” certain items
Step	Action: Requested cash back amount exceeds store policies.
1	The checkout station keypad displays “Problem: Inform clerk”.
2	The clerk tells the customer the maximum allowed cash back amount.
3	The customer enters the maximum cash back amount.

8. Postconditions

1. The customer leaves with purchases and total requested cash back amount.

--- OR ---

2. The customer leaves with purchases and cash back amount less than original request.

--- OR ---

3. The customer leaves with purchases and no cash back.

9. Nonfunctional Requirements

1. The checkout station must respond to the customer’s cash back request within 15 seconds.

2. The clerk must know the maximum allowed cash back amount.

10. Glossary

customer: the actor who wants to pay for purchases with a bank debit card and also wants cash back

clerk: the actor who handles the transaction

bank: the actor that approves the total amount and deducts it from the customer’s account