The name of an action is called an action symbol. The entire collection of action
symbols used by a model program is called its action vocabulary or just its
vocabulary.
5.3.5 Write sample traces
Now that we have identified the actions, we can describe the behavior. Drawing on
our observations and understanding of how the system is supposed to behave, we
write down some traces that the system can execute and that the model program
must also be able to execute. Each trace is simply a sequence of (some of) the actions
from the vocabulary we identified. Here is a sample trace:
ShowTitles(); SortByFirst(); SortByMostRecent(); ShowText();
Not all sequences are allowed, because not all actions are available or enabled in
each state. It is also useful to write down some traces that the model program must
not be able to execute. For example:
ShowTitles(); SortByFirst(); SortByFirst(); ShowText();
The system cannot execute this trace because there are two SortByFirst actions in
succession. After the first, this action is no longer enabled.
It is helpful to refer to these sample traces as we continue the preliminary analysis
and then code the model program. It can also be helpful at this stage to make a table
or a diagram that summarizes many traces, as we show in Chapter 6.
64 Model Programs
5.3.6 Select the state variables
Now we can select the state variables.
Pages:
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106