SYS366 Systems Use Case Descriptions

SYS3662 Contents Review Systems Use Case Descriptions Systems Use Case Authoring

SYS3663 The Process so far Draw Business Use Case Diagram to capture the Business Processes (WP1) Write Business Use Case Descriptions (WP1) Fact Finding Interviewing the Client for Technical, Functional, Data Requirements Identify the functions of the new system Draw Systems Use Case Diagrams (WP2)

SYS3664 Contents Review Systems Use Case Descriptions Systems Use Case Authoring

SYS3665 Systems Use Case Descriptions Accompany the systems use case diagram Lay out the sequence of interaction between the user and the system Diagrams provide high-level view and textual description provides detail

SYS3666 Systems Use Case Descriptions Based on the dialog metaphor

SYS3667 Designing Dialogs The process of designing the overall sequences that users follow to interact with an information system the sequence in which information is displayed to and obtained from the user

SYS3668 Systems Use Case Descriptions The (systems) use case descriptions provide the substance of the (systems) use case model and they are the basis for most of the …modeling work…More than 90% of the (systems) use-case model lies beneath the surface, in the textual use-case descriptions themselves. * *Use Case Modeling, Kurt Bittner & Ian Spence

SYS3669 Systems Use Case Descriptions “The use case description tells a story of how a system and its actors collaborate to achieve a specific goal This collaboration takes the form of a dialog between the system and its actors It is a step-by-step description of a particular way of using a system”* *Use Case Modeling, Kurt Bittner & Ian Spence

SYS36610 Systems Use Case Descriptions “Just like a story, every use case should have a clear beginning (how the actor starts the use case) Middle (how the system and actors work together) End how the use case is concluded”* *Use Case Modeling, Kurt Bittner & Ian Spence

SYS36611 Systems Use Case Descriptions Not a complete description of all possible ways that some task is performed Does not say how the system is designed or implemented Describes typical ways (or cases) of using the system* *Use Case Modeling, Kurt Bittner & Ian Spence

SYS36612 Systems Use Case Descriptions Systems use Case descriptions are required to define, in detail, the processing that needs to happen in each use case The use case diagram provides a quick view of the goal of the use case by examining the case name and associations

SYS36613 Systems Use Case Descriptions The systems use case description must include: Who the actors are and how many of them are interacting with the system at any point in time What data is used and how All normal logic All exception and error logic

SYS36614 Preconditions & Postconditions Preconditions State of the system at the start of use case Postconditions State of the system at the end of use case Can be included in the systems use case description

SYS36615 Preconditions & PostConditions Precondition The user must have been authenticated The user must be authorized The system load is 10% below maximum Postcondition The user’s account has been updated All transactions have been rolled back or committed

SYS36616 Contents Review Systems Use Case Descriptions Systems Use Case Authoring

SYS36617 Systems Use Case Authoring Systems use case descriptions do not pop into existence spontaneously They begin by identifying the use case and create a brief description This description is fleshed out until the final use case description is ready

SYS36618 The Authoring Life Cycle Discovered Briefly Described Bulleted Outline Essential Outline Detailed Description Systems Use Case Specification

SYS36619 Life Cycle: Discovery Through the Table identifying Functions Through experience Shown on a Systems Use Case diagram Place holder for the Systems Use Case description A visual index, providing a context for the descriptions

SYS36620 Life Cycle: Briefly Described Once the Systems Use Case has been identified, it should be described Example: Rent a Video Systems Use Cases This Systems Use Cases describes how a Video Rental Clerk uses the system to identify a customer, process a video, process the payment, produce a rental transaction and produce a receipt.

SYS36621 Life Cycle: Essential Outline Focuses on only the most important behaviour of the system Presents a “black box” view of the system in order to focus on getting right what the system must do Emphasizes usability Helps describe user intent and actions, along with the observable response of the system Does not describe what is happening inside the system

SYS36622 Example: Essential Outline Action by ActorSystem Response Request Customer Information Display Customer Information Provide information on all videos to be rented Record Video information Provide payment detailsRecord payment details Complete TransactionRecord transaction and provide receipt

SYS36623 Essential Outline The use case in point form Very useful for generating user interfaces Too much detail can limit the freedom of the user interface designers Adding details might inadvertently suggest what the interface should look like

SYS36624 Life Cycle: Detailed Description The detailed description fills in the details of the essential outline Begins by expanding the details of the system response Is changed to a narrative form that reads more like a story or a series of detailed steps

SYS36625 Example: Conversational Form Action by ActorSystem Response Request Customer Information Obtain customer name and enter it into system to display information on the customer. Provide information on all videos to be rented Get the list of videos to be rented and enter it into the displayed customer information form. Compute amount owing for rental and tell customer. Provide payment detailsGet credit card, enter into system, and obtain verification. Complete TransactionFinalize transaction, committing it to permanent storage and print receipt for customer.

SYS36626 Example: Narrative Form 1. The customer selects videos and presents them to the clerk. The clerk gets the customer’s name and accesses their customer information on the system. 2. The videos to be rented are entered into the customers information and the amount owing is calculated. The customer is told the amount owing. 3. …..

SYS36627 Life Cycle: Fully Described Fully described use cases are: Testable Understandable Unambiguous Correct Complete attainable

SYS36628 User Interface Mockups A picture of what a user interface will look like Drawn with a tool like PowerPoint Gets feedback on the interface without building it Ensures that the requirements are correctly understood

SYS36629 Drawing Mockups Copy the following graphics to make screen layouts. Button Single-line Edit Box Radio Button (selected) Radio Button (not selected) Multi-line Edit Box -This changes its size according to the typing Check Box (selected) Check Box (not selected) Combo Box List Box Or Combo Box Dropdown Use it either way. Window or Dialog Box

SYS36630 Example: Mockup OK Type your comment here. Halt and Catch Fire Recover Brilliantly Add manual comment to system log: System Recovery Options Recovery Method Cancel

SYS36631 Dialog Charts Layout the sequence of screens displayed to the user Show how user can navigate from one screen to another Each screen symbol contains: Screen name Reference number Numbers of screens user can return to

SYS36632 Dialog Charts

SYS36633 Example: Dialog Chart