This paper argues that a pragmatic approach is needed for integrating design and formalisation of complex systems. We report on our approach to designing the seL4 operating system microkernel API and its formalisation in Isabelle/HOL. The formalisation consists of the systematic translation of significant parts of the functional programming language Haskell into Isabelle/HOL, including monadbased code. We give an account of the experience, decisions and outcomes in this translation as well as the technical problems we encountered together with our solutions. The longer-term goal is to demonstrate that formalisation and verification of a large, complex, OS-level code base is feasible with current tools and methods and is in the order of magnitude of traditional development cost.

Modeling and documentation are two essential ingredients for the engineering discipline of software development. During the last twenty years a wide variety of description and modeling techniques as well as document formats has been proposed. However, often these are not integrated into a coherent methodology with well-defined dependencies between the models and documentations. This hampers focused software development as well as the provision of powerful tool-support. In this paper we present the main issues and outline solutions in the direction of a unified, formal basis for software and system modeling.