ZUM ’98: The Z Formal Specification Notation : 11th International Conference of Z Users Berlin Germany September 24 26 1998. Proceedings This book constitutes the refereed proceedings of the 11th International Conference of Z Users ZUM 98 held in Berlin Germany in September 1998. The 28 revised and invited papers presented were carefully reviewed and selected for inclusion in the book; also included is a comprehensive Z bibliography and a summary of the frequently asked questions at two Z Internet sites. The papers are organized in sections on industrial issues concurrency tools Z and HOL safety critical and real time systems semantic theory theory and standards reasoning and consistency issues refinement and object orientation