A method for simulating operation of a system. The method accesses information characterizes system behavior, identifies system components and characterizes component behavior and relationships. The components include composite or non-composite unit types. A user selects an instance root and the method induces an instance hierarchy from that root. The instance hierarchy is displayed on a GUI in the form of a navigable tree or breadcrumbs view. Operation of the system is simulated using the instance hierarchy. Embodiments further include the concepts of merging certain variable names, displaying producing and consuming downstream and upstream elements, positioning, rotating, or orienting diagram elements to avoid overlapping with other diagram elements, identifying statically constant variables and propagating constness to producer and consumer variables, storing simulation results in compressed form and decompressing as needed, and identifying differences between dataflow diagrams.