Developing Components in the Presence of Re-entrance

Independent development of components according to their speci cations is complicated by the fact that a thread of control can exit and re-enter the same component. This kind of re-entrance may cause problems as the internal representation of a component can be observed in an inconsistent state. We argue that the ad-hoc reasoning used in establishing conformance of components to their speci cations that intuitively appears to be correct does not account for the presence of re-entrance. Such reasoning leads to a con ict between assumptions that component developers make about the behaviour of components in a system, resulting in the component re-entrance problem. We formulate the modular reasoning property that captures the process of independent component development and introduce two requirements that must be imposed to avoid the re-entrance problem. Then we de ne a customised theory of components, component systems, and component re nement which models the process of component development from speci cations. Using this theory, we prove that the formulated requirements are su cient to establish the modular reasoning property.