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SYS366

SYS366. Last Lecture System Use Descriptions created through Use case Authoring. Today. Systems Use Case Descriptions Systems Use Case Authoring. Systems Use Case Diagrams and Descriptions. Based on the dialog metaphor. Dialog Expresses that the User and Computer

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SYS366

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  1. SYS366 Last Lecture System Use Descriptions created through Use case Authoring

  2. Today • Systems Use Case Descriptions • Systems Use Case Authoring

  3. Systems Use Case Diagrams and Descriptions • Based on the dialog metaphor

  4. Dialog Expresses that the User and Computer Interact by Sending Messages

  5. 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

  6. Sequence • understanding how the user will interact with the system • clear understanding of user, task, technological and environmental characteristics

  7. 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, Addison-Wesley, 2003, p. 30

  8. Systems Use Case Descriptions • “(Systems) use cases are more than just a named ellipse and a brief description. For each (systems) use case there will also be a (systems) use-case description where the full story of the use case is told.”* *Use Case Modeling, Kurt Bittner & Ian Spence, Addison-Wesley, 2003, p. 30

  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, Addison-Wesley, 2003, p. 24

  10. Systems Use Case Description • 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, Addison-Wesley, 2003, pp. 24-25

  11. Systems Use Case Descriptions • Systems use Case descriptions are required to define, in detail, the processing that needs to happen in each use case

  12. 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

  13. Today • Systems Use Case Descriptions • Systems Use Cases Authoring

  14. Systems Use Cases Authoring • The Systems Use Cases and its description evolves through the authoring process.* *Systems Use Cases Modeling by Bittner & Spence, Page 152

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

  16. The Authoring Life Cycle • State 1: Discovered * • Through the Actor/Function/Use Case Table • 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 *Systems Use Cases Modeling by Bittner & Spence, Pages 153 - 154

  17. The Authoring Life Cycle • State 2: Briefly Described • Once the Systems Use Case has been identified, it should be described

  18. The Authoring Life Cycle • State 3: 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

  19. The Essential Outline • Stripped down essential outlines capture the essence of the required dialog without forcing the designers into any particular technology or mode of interaction

  20. The Detailed Description • State 4: Detailed Description • Start adding to the (Essential) outline the detail required to complete the Description of the system • Here the use case is evolving as more and more detail is added to flesh out the outline

  21. The Use Case Description • State 6: Fully Described • The final state in the evolution of a use case • The use case has a complete flow of events • Unambiguously defines all of the inputs and outputs involved in the flow of events.

  22. 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, Addison-Wesley, 2003, p. 24

  23. 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, Addison-Wesley, 2003, p. 24

  24. Use Case Descriptions • The major sections of a use case Description are: • Brief Description • Precondition statement • Main flow • Subflows • Exceptions • Successful post conditions

  25. The Main Flow The main flow describes: • How the use case starts • What events initiate system activity • What system activity each event initiates The main flow describes the logic that controls the use case activity

  26. Subflows • Describe a piece of system activity • Only some subflows are initiated from the main flow • Subflows can initiate other subflows or they can initiate another use case

  27. Subflows • Must be specific. You must describe how each ends. • A subflow might: • Restart itself, another subflow or the use case • Continue the use case from the insertion point • End the use case • Launch another use case

  28. Exceptions • Describe how the system handles user errors and unexpected system responses

  29. Use Case Description • 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, Addison-Wesley, 2003, pp. 24-25

  30. The Use Case Description • Fully Described • One of the best checks of whether a use case Description is finished is to ask if you could use the use case to derive system tests.

  31. The Use Case Description • Fully Described • The best way to tell if the use cases fit the purpose is to pass them along to the …test team for test design. • If the team is satisfied that they can use the use cases to support this activity, then the use case Description contains sufficient levels of detail.

  32. The Use Case Description • State 6: Fully Described • One of the best checks of whether a use case Description is finished is to ask if you could use the use case to derive system tests. • The best way to tell if the use cases fit the purposed is to pass them along to the

  33. Use Case Description • Place Bid Example

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