Quelli che s'innamoran di pratica senza scienzia sono come 'l nocchieri ch'entra in navilio sanza timone o bussola, 1 che mai ha certezza dove si vada. - Leonardo da Vinci Ich habe oft bemerkt, dass wir uns durch allzuvieles Symbolisieren 2 die Sprache fu ¨r die Wirklichkeit untu ¨chtig machen. - Christian Morgenstern This is the place to express our thanks. First of all we thank all those who over the years have actively contributed to shaping the novel software design and analysis method explained in this book. They are too numerous to be mentioned here. They all appear in some way or the other on the following pages, in particular in the bibliographical and historical Chap. 9 which can be read independently of the book. We then thank those who have helped with detailed critical comments on the draft chapters to shape the way our arguments are presented in this book: M. B¨ orger (Diron Mu ¨nster), I. Craggs (IBMHursley),G. DelCastillo(SiemensMunc ¨ hen),U. Gl¨ asser(SimonFraser University, Vancouver,Canada),J. Huggins(Kettering University,Michigan, USA), B. Koblinger (IBM Heidelberg), P. Pa ¨ppinghaus (Siemens Munc ¨ hen), A. Preller (Universit´ e de Montpellier, France), M. -L. Potet (INP de Gre- ble, France),W. Reisig (Humboldt-Universit¨ at zu Berlin, Germany),H. Rust (Universit¨ at Cottbus, Germany), G. Schellhorn (Universit¨ at Augsburg, G- many), B. Thalheim (Universit¨ at Cottbus, Germany) and a dozen student generationsat Universita `di Pisa. We thankM. Barmet(ETH Zur ¨ ich)for her solutions of the exercises in Chap. 8. We also thank L.