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

Agenda Describing Use Cases

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

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

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.

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

Online Auction Example: Use Case Diagram

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)

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 A2 Nikon Digital Category Page Exit Photography Category: Exit Display 2nd

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

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?

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.

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

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.

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?