Instead, we
select a subset of related features that comprise a self-contained package of functionality.
A large implementation can be covered by several small model programs
that represent different subsets of features. Choose a feature subset that makes a
62 Model Programs
reasonable work assignment. For example, a tester would choose a collection of
features that would be covered by a typical test suite. The chosen subset of features
is sometimes called a slice (of the implementation??™s complete feature set).
For this example, we choose a very small subset of newsreader features: the
screens, styles, and options described in Section 5.2. This is an unusually small
collection of features for a model program that we chose to make this example brief.
5.3.3 Choose a level of abstraction
Even when we limit ourselves to a subset of features, we do not consider every
implementation detail in that subset. We must decide which details to include in
the model program; other details can be omitted or greatly simplified. This is called
abstraction; our choice of which details to include defines the level of abstraction. A
lower level shows more detail, and results in a larger, more complex model program.
A higher level shows less detail, and results in a smaller, simpler model program.
Working at a higher level of abstraction is easier because there is less information
to deal with.
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