Object-based sequential programming has had a major impact on software engineering. However, object-based concurrent programming remains elusive as an effective programming tool. The class of applications that will be implemented on future high-bandwidth networks of processors will be significantly more ambitious than the current applications (which are mostly involved with transmissions of digital data and images), and object-based concurrent programming has the potential to simplify designs of such applications. Many of the programming concepts developed for databases, object-oriented programming and designs of reactive systems can be unified into a compact model of concurrent programs that can serve as the foundation for designing these future applications. We propose a model of multiprograms and a discipline of programming that addresses the issues of reasoning (e.g., understanding) and efficient implementation. The major point of departure is the disentanglement of sequential and ...