Formal Methods for Open Object-Based Distributed Systems IV presents the leading edge in the fields of object-oriented programming, open distributed systems, and formal methods for object-oriented systems. With increased support within industry regarding these areas, this book captures the most up-to-date information on the subject. Papers in this volume focus on the following specific technologies: components; mobile code; Java(R); The Unified Modeling Language (UML); refinement of specifications; types and subtyping; temporal and probabilistic systems. This volume comprises the proceedings of the Fourth International Workshop on Formal Methods for Open Object-Based Distributed Systems (FMOODS 2000), which was sponsored by the International Federation for Information Processing (IFIP) and held in Stanford, California, USA, in September 2000.