Software Design 2e - DIM

322Jackson System Development (JSD)Figure 15.8A simple example of a segment from an SSD.multiple inputs through one read operation, while in the latter it must organize thesequencing of consumption from the two sources. However, beyond observing thepresence of these structures, we will not explore the SSD notation in any further depthin this chapter.Figure 15.8 shows an SSD describing a very simple network in a system. Thecircle is used to label a data-flow arc, and an entity is represented by using an oblongbox. Those who are more accustomed to the conventional DFD notations might findthis confusing. The diamond shape used to describe the state vector is associated witha particular entity by means of the labelling attached to it.15.3 The JSD processThe procedures involved in the ‘process part’ of JSD have undergone a certain amountof revision and repackaging since the method was first introduced. Figure 15.9 uses anESD to describe the JSD process as it was originally presented in Jackson (1983), whileFigure 15.10 shows the form of the method as subsequently described in Cameron(1986). Two basic changes occurred in the method during this interval.