This example presents an interactive system dynamics model of a grass-sheep ecosystem using the GoJS diagramming library alongside D3. The visualization distinguishes between stocks (grass, sheep), clouds (external sources/sinks), valves (flow regulators), and variables (weather, wolves) that influence connections. Users can modify the underlying JSON model data, which defines nodes and links—both material flows and causal influences—and redraw the diagram. The interface supports creating new nodes and links via buttons, with custom categorization for flows versus influences, while a label-dragging tool adjusts node annotations.