Chapter 10 System Sequence Diagrams

What is a System Sequence Diagram? A way of modeling input and output events related to systems It is a picture that shows, for one particular use case scenario, the events an external actor generates and in what order. Draw SSD for the main success scenario and complex alternative ones. They show the system as a black box. There should be one for the main success scenario of a use case. Like Domain Models – very high level with a lower level counterpart

Fig. 10.1

Fig. 10.2

Why Draw SSDs? Easy way to capture external events like “customer arrives at CheckOut”. A description of “what” the system does but with some time aspects. UML does not have separate notation.

Relationship between DM and SSD. SSDs are usually related to a single scenario of some Use Case The following is the success scenario for POS

Fig How to represent loops

Fig Naming System Events too physical abstract intention

Fig. 10.5