Specifications are not (necessarily) executable

Specifications can be written in languages which have formal semantics. Their very formality, and the similarities with some aspects of implementation languages, invites the idea that specifications might be executed. This paper presents a number of arguments against that idea. The aim is to warn of the dangers of limiting specification languages to the point where all of their constructs can be executed. While conceding the difficulties of relating specifications to an understanding of the ‘requirements’ for a system, it is argued that other solutions should be sought than ‘executable specification languages’.