In the last chapter we started to relax the assumption of conformity, that is the idea that the abstract and concrete data types should have corresponding sets of operations, by introducing internal operations into our specifications. In this chapter we go one step further and consider the idea of non-atomic refinements where conformity is abandoned completely and the abstract and concrete specifications have different sets of observable operations. The particular case we will be interested in is when an abstract operation is refined by not one, but by a sequence of concrete operations thus allowing a change of granularity when we develop a specification.
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