A Theory and Practice of Program Development provides a comprehensive introduction to a software development method based on VDM-SL. Each development step is rigorously justified, and the strategies and transformations used are justified and explained ma thematically. The approach provides the formal semantics of a simple, but powerful, wide-spectrum programming language and gives a formal definition of both algorithmic and data refinement. Unlike other texts, it covers both the theory and practice of program development. Although based on VDM-SL, no knowledge of this language is assumed, thus making it widely accessible. A Theory and Practice of Program Development is intended for 3rd/4th year undergraduate and postgraduate students taking formal methods and software engineering; software developers involved in the production of provably correct computer systems and reusa ble design and the problems of reusable code.

SoSL was the first International Workshop on Semantics of Specification Languages, held from 25-27 October 1993 in Utrecht, the Netherlands. The workshop was organized by the Department of Philosophy of Utrecht University with financial support from the Nationale Faciliteit Informatica of the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), and under the auspices of the British Computer Society'S specialist group in Formal Aspects of Computing Science (BCS FACS). The concern of the workshop was the semantics of specification languages, and the issues closely related to this area, such as type checking and the justification of proof rules and proof obligations. Its aim was the exchange of problems and ideas in this field of formal methods, and the identification of common programs of work for further investigation. The program of SoSL consisted of 3 invited lectures presenting the developments of the semantics of 3 major specification languages. Furthermore, there were 16 presentations of submitted papers. This volume provides a direct account of the workshop. It contains 3 papers that match the invited lectures and the 16 selected papers. The editors want to thank all those who have contributed to the workshop; the Program Committee and the referees for selecting the contributed papers, the invited speakers for their interesting talks, the Organizing Committee for all their efforts, and of course the participants. We have the feeling that the workshop was worthwhile and should be repeated.

3. 1 What are formal methods? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3. 2 A survey of formal methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3. 2. 1 FDTs and FSLs for sequential software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3. 2. 1. 1 VDM (Vienna Development Method). . . . . . . . . . . . . . . . . . . . . 19 3. 2. 1. 2 Z. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3. 2. 1. 3 me too . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3. 2. 1. 4 HOS and AXES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3. 2. 1. 5 Gist. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3. 2. 1. 6 Clear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. 2. 1. 7 OBJ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. 2. 1. 8 ACT ONE and ACT TWO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. 2. 1. 9 CIP-L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. 2. 1. 10 LPG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. 2. 1. 11 Larch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. 2. 1. 12 Logic languages-the Prolog family. . . . . . . . . . . . . . . . . . . 22 3. 2. 1. 13 Functional languages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3. 2. 2 FDTs and FSLs for concurrent software. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3. 2. 2. 1 LOTOS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3. 2. 2. 2 Estelle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3. 2. 2. 3 SDL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3. 2. 2. 4 ASN. l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3. 2. 2. 5 TTCN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3. 2. 2. 6 Gypsy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3. 2. 3 Graphical formalisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3. 2. 3. 1 Petri nets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3. 2. 3. 2 Higraphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3. 2. 4 Less formal methods and notations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3. 2. 4. 1 SADT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3. 2. 4. 2 Structured Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3. 2. 4. 3 SSADM and LSDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3. 2. 4. 4 JSPandJSD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3. 2. 4. 5 HDM and the SPECIAL language . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3. 2. 4. 6 Structured analysis and design of real-time systems. . 27 3. 3 Support tools for FDTs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .