Systems Analysis and Synthesis

7.6. Modes

Suppose that, in order to detect and deal correctly with erroneous events, the Bursary also uses a batch processing system like that just described in Figure 7.12. In particular, the system checks the value of Candidate State before updating Balance Owing. The batch system proposed in Figure 7.12 accesses these two Candidate attributes in two separate update processes.

Now suppose that the Bursary becomes responsible for deciding whether candidates can graduate. This is reasonable, because it is a kernel requirement that a candidate cannot graduate until all fees have been paid — a financial matter, making it the responsibility of the Bursary. This requires Balance Owing to be inspected before updating Candidate State — the reverse of ...