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PRJ566

PRJ566. System Sequence Diagrams. System Sequence Diagrams. A system sequence diagram …. Illustrates input and output events related to the system under discussion. Larman, APPLYING UML AND PATTERNS, p. 173. System Sequence Diagrams.

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PRJ566

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  1. PRJ566 System Sequence Diagrams

  2. System Sequence Diagrams • A system sequence diagram …. Illustrates input and output events related to the system under discussion. • Larman, APPLYING UML AND PATTERNS, p. 173

  3. System Sequence Diagrams • The use case text and its implied system events are input to a SSD (system sequence diagram). • Larman, APPLYING UML AND PATTERNS, p. 17

  4. System Sequence Diagrams • Use cases describe how external actors interact with the software system… • An actor generates system events to a system, requesting some system operation to handle the event. • The use case text implies the event…the SSD makes it concrete and explicit. • Larman, APPLYING UML AND PATTERNS, p. 176

  5. System Sequence Diagrams • A system sequence diagram is a picture that shows, for one particular scenario of a usecase, the events that external actors generate, their order and the inter-system events. • All systems are treated as a black box. • Larman, APPLYING UML AND PATTERNS, p. 176

  6. Why Draw System Sequence Diagrams? • The external input events—the system events are an important part of analyzing system behavior. • System behavior is a description of what a system does, without explaining how it does it. • Larman, APPLYING UML AND PATTERNS, p. 173

  7. System Sequence Diagrams • System events should be expressed at the abstract level of intention rather than in terms of the physical input device. • Larman, APPLYING UML AND PATTERNS, p. 178

  8. System Sequence Diagrams • How to name system events and operations • describe at a high level i.e. enterItem instead of scanItem • ‘enter’ captures the intent of the operations without specifying a design choice (i.e. scanning)

  9. System Sequence Diagram • Shows the external actors that interact directly with the system • Shows the ‘system’ • Shows the system events that the actors generate • Done in a chronological sequence (from first to last event over time) • Order of events should follow the order of the scenario

  10. System Sequence Diagrams • Validates use cases • helps identify processing that has not been covered by the process described in the use case • Helps us identify objects and classes

  11. Browse Catalog SSD

  12. How Many System Sequence Diagrams? One for each of the HD scenarios in the use case specification • Larman, APPLYING UML AND PATTERNS, p. 176

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