1. SYS466: Analysis and Design Using OO Models
Lecture 2
Use Case Descriptions

2. Agenda
Describing Use Cases

3. Use Case Description A powerful technique to identify:
All the success and failure tasks to be performed by a use case
All the actors and how they interact with the use case
Can be brief, casual or fully dressed
Documented using a Use Case Description Template – text based

4. Use Case Description Brief Use Case Description:
A one-paragraph summary of the main success ‘scenario’ of the use case
Casual Use Case Description:
A multi-paragraph summary that covers various ‘scenarios’ of the use case
Fully Dressed Use Case Description:
All steps and variations of the use case written in detail

5. Use Case Description
Sections of the fully dressed use case description:
Brief Description
Pre-conditions
Basic Flow
Sub Flows
Error Conditions
Successful Post Conditions
A scenario is “ a sequence of actions that illustrates behavior. A scenario
may be used to to illustrate an interaction or the execution of a use case
instance”, Rumbaugh, J. et al. The Unified Modeling Language -
Reference Manual.

6. Use Case Description Steps for developing a use case description:
Identify the actor(s) who initiate the use case (see use case diagram)
Identify the actor(s) who may be involved (see use case diagram)
Identify the precondition – the state the system is in before the use case begins
Determine how the use case should end – this statement becomes your successful post condition
Describe the normal success steps first (Basic Flow)
For each step, identify possible variations and error conditions

7. Online Auction
Example:
Use Case Diagram

8. Online Auction Example: Browse Catalog Use Case
Always prepare mockups before you start writing the description! It is important to understand what the user is doing to interact with the system.
When a shopper wants to browse the catalog, the actor needs to select a category, and then from within a category, select an item and then from a list of items, select the specific item they want to see
Always describe the normal course of events first (Basic Flow in a full use case description)

9. Online Auction Example: Browse Catalog Use Case
Sample screen mock ups:
Online Auction Main Page
Browse Catalog
Exit
Item List Page
1st
3rd
Items:
Canon SLX Canon TXC
Kodak Digital Kodak 347
Nikon A Nikon Digital
Category Page
Exit
Photography
Category:
Exit
Display
2nd

10. Online Auction Example: Browse Catalog Use Case
The Process—Normal Course
Shopper selects browse catalog option
Shopper selects a category to view
Shopper selects an item to view

11. Online Auction Example: Browse Catalog Use Case
The Process—Error Conditions
What if the shopper does not select a category?
What if no items are found for that category?
What if the shopper does not select an item?
What if the shopper cancels the browse?

12. Online Auction Example: Place Bid Use Case
When a shopper wants to place a bid on an item, the actor needs to be registered as a buyer and they must be logged in. Once all this happens, they can see the current high bid for the item and then they can place their own bid.

13. Online Auction Example: Place Bid Use Case
Place Bid Page
Exit
Shopper ID:
Item: Canon SLX
Description:
Camera uses 35mm
film and has a built in flash.
Picture goes here
Sample screen mock ups:
2nd
Item Information Page
Item: Canon SLX
Description:
Camera uses 35mm
film and has a built in flash.
Picture goes here
1st
Place Bid Page
Exit
Shopper ID:
Item: Canon SLX
Description:
Camera uses 35mm
film and has a built in flash.
Picture goes here
Current Bid: $135.00
New
Bid:
Save Bid
3rd
Exit
Place Bid

14. Online Auction Example: Place Bid Use Case
The Process—Normal Course
Shopper selects place bid option
Shopper is identified as a member
Shopper is logged on
The shopper views an item’s current high bid.
The shopper makes a new bid
The shopper confirms the bid request
The old highest bid is replaced with the new bid.

15. The Process—Error Conditions
What if the shopper is not a member?
What if the shopper is not logged on?
What if the shopper’s bid is invalid?
What if the shopper cancels the bid request instead of confirming?
What if the bid cannot replace the old bid?