Over the past three decades, software engineers have derived a progressively better understanding of the characteristics of complexity in software. It is now widely recognised thatinteraction is probably the most important single char- teristic of complex software. Software architectures that contain many dyna- cally interacting components, each with their own thread of control, and eng- ing in complex coordination protocols, are typically orders of magnitude more complex to correctly and e?ciently engineer than those that simply compute a function of some input through a single thread of...