Data Refinement of Predicate Transformers

Abstract Data refinement is the systematic substitution of one data type for another in a program. Usually, the new data type is more efficient than the old, but also more complex; the purpose of data refinement in that case is to make progress in a program design from more abstract to more concrete formulations. A particularly simple definition of data refinement is possible when programs are taken to be predicate transformers in the sense of Dijkstra. Central to the definition is a function taking abstract predicates to concrete ones, and that function, a generalisation of the abstraction function, therefore is a predicative transformers as well. Advantages of the approach are: proofs about data refinement are simplified; more general techniques of data refinement are suggested; and a style of program development is encouraged in which data refinements are calculated directly without proof obligation.