Structured Interacting Computations

Today, concurrency is ubiquitous, in desktop applications, client-server systems, workflow systems, transaction processing and web services. Design of concurrent systems, particularly in the presence of communication failures, time-outs and interrupts, is still difficult and error-prone. Theoretical models of concurrency focus on expressive power and simplicity, but do not provide high-level constructs suitable for programming. The authors have been developing a theory, called Orc (for orchestration), and its practical applications. In this paper, the authors describe their philosophy in designing Orc.