Specification by interface separation

In specifying an operation it is often advantageous to describe it with abstract inputs and outputs whose concrete representation is described separately. For example, it is often convenient to describe as a set, input which in practice occurs as a sequence. The primary advantage of this approach is that one can initially concentrate on specifying an operation without the representations of its interface (that is, its inputs and outputs) obscuring the more important concerns of its abstract functional properties. Interface representations can be tackled independently, after the abstract functionality has been decided. Such separation of an operation into an abstract core and its interface with its environment makes the task of specification simpler, aids clarity of the result, and encourages reuse of both the abstract operation and its interface descriptions.