Abstract: Interactive event-driven programs are structured and executed using two types of constructs: interconnectable processing components and flow objects with associated data. Components are interconnected in a hierarchical dataflow network, and references which provide access to flow objects flow on the interconnections. Response to events and bidirectional coordination over multicomponent data paths, even in a distributed object system, employ unidirectional dataflows and intercomponent message sequences mediated by flow objects. Scaling and abstraction of complexity are facilitated by encapsulation of constructed networks into new component definitions. An interactive debugger preserves state as an executing program is edited, permitting an event-driven program to be modified in the intervals between processing of events without reinitialization.