The set of all possible input states is known as the input space, illustrated here. Similarly an output variable is a variable that exists external to a program and is set by it. An output state is a set of values of all output variables associated with a run of a program. The run types required of the program by the environment can be viewed as being selected randomly. Thus, we define the operational profile as the set of run types that the program can execute along with the probabilities with which they will occur. In the figure, we show two of many possible input states, A and B, with their probabilities of occurrence.

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