Scientific visualization and simulation frameworks mostly use data/event ow mechanisms for simulation specification, control, and interactivity. Even though object orientation powerfully and elegantly models many application domains, integration of OO libraries in such systems remains difficult. The elegance and simplicity of OO design gets lost in the integration phase, as most systems do not support combination of OO and dataflow concepts.We propose a general-purpose OO visualization and simulation system which addresses simulation design, control and interactivity by merging OO and data ow modelling in a single abstraction. The system's advantages over similar ones are illustrated by a comprehensive set of examples.