This volume contains the proceedings ofthe 4th Refinement Workshop which was organised by the British Computer Society specialist group in Formal Aspects of Computing Science and held in Wolfson College, Cambridge, on 9-11 January, 1991. The term refinement embraces the theory and practice of using formal methods for specifying and implementing hardware and software. Most of the achievements to date in the field have been in developing the theoretical framework for mathematical approaches to programming, and on the practical side in formally specifying software, while more recently we have seen the development of practical approaches to deriving programs from their speCifications. The workshop gives a fair picture of the state of the art: it presents new theories for reasoning about software and hardware and case studies in applying known theory to interesting small-and medium-scale problems. We hope the book will be Of interest both to researchers in formal methods, and to software engineers in industry who want to keep abreast of possible applications of formal methods in industry. The programme consisted both of invited talks and refereed papers. The invited speakers were Ib S0rensen, Jean-Raymond Abrial, Donald MacKenzie, Ralph Back, Robert Milne, Mike Read, Mike Gordon, and Robert Worden who gave the introductory talk. This is the first refinement workshop that solicited papers for refereeing, and despite a rather late call for papers the response was excellent. The Process of Refinement: Introductory Talk to the 4th Refinement Workshop.- Engineering Real Software Using Formal Methods.- Specialising Abstract Programs.- A Refinement Case Study (Using the Abstract Machine Notation).- Assertional Data Reification Proofs: Survey and Perspective.- Formal Methods and the Sociology of Proof.- Refinement Diagrams.- A Case Study in Timed Refinement: A Central Heater.- Object Oriented Specification and Refinement.- The Ecology of Class Refinement.- Transforming Axioms for Data Types into Sequential Programs.- Refinement of Two Graph Problems.- CSP and Timewise Refinement.- The Elusive Software Refinery: A Case Study in Program Development.- A Theory of State-based Parallel Programming: Part 1.- Design, Verification and Documentation of Concurrent Systems.- A Formal Method for Hard Real-Time Programming.- Constructing and Refining Modules in a Type Theory.- The Varieties of Refinement.- Timed Process Algebra, Petri Nets and Event Refinement.- Author Index.
