Model-based specification

The classical specification formalism involving pre- and postconditions expressed in program variables cannot directly be applied to the specification of classes, interfaces, components, and design patterns, since the program variables involved are mostly invisible outside of (dynamically selected) implementation code. A more useful specification formalism, operating at the problem domain level rather than at the implementation level, is proposed and it is shown how this can be used for Dijkstra-style derivation of object-oriented code.