The correct development of large / com plex pieces of software demands a thorough structuring of the design process. In a first phase the requirements engineering is relevant for capturing the relevant functionality and its adequate formalization in precise mathematical definitions. Prototyping can can be used as a means for checking the functional behaviour at this early stage of development. The ade quate specification resulting from the first phase is then the basis for the second phase which comprises the derivation of an implementation. This phase requires the use of formal methods and...