We choose a high level of behavioral
abstraction where each action in the model program represents a large amount of
implementation behavior. Each action represents both the selection of an option that
causes a new page (or a different page style) to appear, and the appearance of that
page.
In every model program, we use the same high level of environmental abstraction.
There is no main method, nor any other control structure that determines the sequence
in which actions occur (methods are called). Instead, the model program has enabling
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conditions, which allow the sequence of method calls to be chosen at run time by
the tool that executes the model program, or by the environment where the model
program runs.
5.3.4 Select the actions
It is often easier to select the actions first, because we can identify them by simply
observing the behavior. Recall that we choose a high level of behavioral abstraction
where each action is the selection of an option that causes a new screen to appear.
We select these actions:
The SelectMessages and SelectTopics actions select those pages; these are the
actions that occur when users click on a topic title or the group name, respectively.
ShowTitles and ShowText select the details shown on the topics page. SortByFirst
and SortByMostRecent select the sort order for the topics page when the titles only
are shown.
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