A Half Century of Formal Methods

In this '45 Years of Formal Methods' review we first delineate what we mean by method, formal method, computer science, computing science, software engineering, and model-oriented and algebraic methods. Based on this we shall characterise a spectrum from specification-oriented methods to analysis-oriented methods. Then we shall provide an Overview: which are the `prerequisite works' that have enabled formal methods; and which are, to us, the, by now, classical formal Specification and Analysis Methods. We then ask ourselves the question: A Success Story? Have formal methods for software development, in the sense of this paper been successful? Our answer is a guarded yes. At the start of More Personal Observations, we relate, in The DDC Ada Story, a 1980--1984 formal methods success story. We motivate the guarded answer by discussing Some Obstacles to Formal Methods in university research and education as well as in industry practice. Finally we discuss current programming language developments in a Next 10 Years perspective. Although some of these trends have occurred in parallel with formal methods development, and seemingly independent thereof, we do see some convergence.