You should always write your model program at the highest level
of abstraction that achieves your purpose (that can answer the questions you have
formulated). Much of the skill in modeling is understanding what can be left out in
order to achieve the right level of abstraction.
We use three kinds of abstraction. Data abstraction deals with variables. A higher
level of data abstraction uses fewer variables, fewer values for those variables, and
simpler data types. Data abstraction is our primary technique for finitizing models:
we replace a potentially ???infinite???collection of values with a (usually small) finite
collection. Behavioral abstraction deals with statements and methods.Ahigher level
of behavioral abstraction uses fewer statements or methods, where each statement or
method in the model program represents more behavior in the implementation. Environmental
abstraction deals with control structure. A higher level of environmental
abstraction removes control structure, leaving it to the tool or the environment
to choose which methods to execute at run time. In other words, environmental
abstraction replaces control structure with nondeterminism.
In this example we choose a high level of data abstraction where the variables
only represent the kind of page that is displayed and its style. We do not represent
the page contents (the topics and messages).
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