A Plea for Grey-Box Components

Interface Description Languages (IDLs) describe the syntactic part of a component’s interface, but they do not help to specify semantics. Additional informal descriptions or preand postconditions of operations are often not precise enough. For instance, they cannot properly describe call-back scenarios, that is, the states, at which external calls are made, and the sequence of calls. Revealing the full implementation, that is, the source code, on the other hand, overspecifies the component and, thus, prohibits alternative implementations and future enhancements. What is needed is a language that allows to reveal as much of an implementation as is required to use a component, but not more. Such a language can be found in the theory of program refinement, but this is rarely used with commercial software because of the human factor: the notation is very symbolic instead of resembling a known implementation language. The lack of tool support for simulating specifications and for automatic refinement proofs also limits the enticement of writing specifications.