1. BTS430 Systems Analysis and Design using UML
System Sequence Diagrams

2. AGENDA Use Case Specifications returned
Introduction of System Sequence Diagrams
Exercises

3. 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

4. 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. 174

6. 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

7. System Sequence Diagrams
A system sequence diagram is a picture that shows, for one particular scenario of a use case, 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

10. 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

11. 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

13. How Many System Sequence Diagrams?
One for each frequent scenario
One for each complex scenario
Larman, APPLYING UML AND PATTERNS, p. 176