8. system sequence diagrams
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System sequence diagrams (SSDs) illustrate input and output events between systems and actors. SSDs are drawn for main and alternative use case scenarios to show the events coming into a system and the system's response without detailing how it works internally. Defining a system's behavior through SSDs early in design allows investigation of what events a system must handle at a high level before proceeding to more detailed design.
8. system sequence diagrams
- 1. System Sequence Diagrams Fakultas Ilmu Komputer Universitas Sriwijaya 2008
- 3. Example: Main success scenario of a cash-only process sale scenario
- 4. What Are System Sequence Diagrams? • A system sequence diagram (SSD) is a fast and easily created artifact that illustrates input and output events related to the systems under discussion. • Use cases describe how external actors interact with the software system we are interested in creating. • During this interaction an actor generates system events to a system, usually requesting some system operation to handle the event. • Guideline: Draw an SSD for a main success scenario of each use case, and frequent or complex alternative scenarios.
- 5. Why Draw an SSD? (1) • An interesting and useful question in software design is this: What events are coming in to our system? Why? Because we have to design the software to handle these events (from the mouse, keyboard, another system, …) and execute a response.
- 6. Why Draw an SSD? (2) • Before proceeding to a detailed design of how a software application will work, it is useful to investigate and define its behavior as a "black box." • behavior is a description of what a system does, without explaining how it does it
- 7. Relationship Between SSDs and Use Cases?
- 8. How to Name System Events and Operations