4. Formal development

4.1 Formal methods

Formal methods are becoming increasingly popular, particularly in critical applications such as nuclear power plants, avionics and rail transport. The problem with mission-critical applications is to guarantee maximum operational safety. The contribution of formal methods is to provide a mathematical framework for the development process, enabling the production of software that is correct by construction, thanks to a development process that can be verified by validation techniques such as proof or model exploration. To achieve this, it is obviously necessary to describe precisely the properties that the software system must possess. Formal methods fall into several categories:

• algebraic specifications (PLUSS or PVS)...