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SYS366

SYS366. Systems Use Case Descriptions. Contents. Review Systems Use Case Descriptions Systems Use Case Authoring. The Process so far. Draw Business Use Case Diagram to capture the Business Processes (WP1) Write Business Use Case Descriptions (WP1) Fact Finding

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SYS366

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  1. SYS366 Systems Use Case Descriptions

  2. Contents • Review • Systems Use Case Descriptions • Systems Use Case Authoring SYS366

  3. 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) SYS366

  4. Contents • Review • Systems Use Case Descriptions • Systems Use Case Authoring SYS366

  5. 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 SYS366

  6. Systems Use Case Descriptions • Based on the dialog metaphor SYS366

  7. 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 SYS366

  8. 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 SYS366

  9. 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 SYS366

  10. 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 SYS366

  11. 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 SYS366

  12. 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 SYS366

  13. 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 SYS366

  14. 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 SYS366

  15. 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 SYS366

  16. Contents • Review • Systems Use Case Descriptions • Systems Use Case Authoring SYS366

  17. 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 SYS366

  18. The Authoring Life Cycle Discovered Briefly Described Essential Outline Bulleted Outline Detailed Description Systems Use Case Specification SYS366

  19. 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 SYS366

  20. 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. SYS366

  21. 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 SYS366

  22. Example: Essential Outline SYS366

  23. 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 SYS366

  24. 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 SYS366

  25. Example: Conversational Form SYS366

  26. Example: Narrative Form • 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. • The videos to be rented are entered into the customers information and the amount owing is calculated. The customer is told the amount owing. • ….. SYS366

  27. Life Cycle: Fully Described • Fully described use cases are: • Testable • Understandable • Unambiguous • Correct • Complete • attainable SYS366

  28. 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 SYS366

  29. Radio Button (selected) Check Box (selected) Check Box (not selected) Drawing Mockups • Copy the following graphics to make screen layouts. Button Single-line Edit Box Multi-line Edit Box -This changes its size according to the typing Radio Button (not selected) Window or Dialog Box Combo Box List Box Or Combo Box Dropdown Use it either way. SYS366

  30. Example: Mockup System Recovery Options Recovery Method OK Halt and Catch Fire Recover Brilliantly Cancel Add manual comment to system log: Type your comment here. SYS366

  31. 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 SYS366

  32. Dialog Charts SYS366

  33. Example: Dialog Chart SYS366

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