Constraint-based architectures have long been used for 2D graphics systems (see for a survey). In the 3D graphics world, one-way constraints are commonly employed to maintain dependencies between components . This type of constraint cannot easily model mutual relations between objects, thus hindering the tight coupling between user-interface and application objects . Our system uses instead multi-way local propagation constraints, which offer support for two-way communication between objects while remaining efficient enough to ensure the responsiveness of the system . TBAG also uses multi-way constraints maintained by Skyblue , but its functional approach concentrates more on modeling time - varying behaviors than on creating interactive systems. Much effort has been spent in developing powerful numerical solvers for computer graphics . This work is complementary to ours, which focuses more on providing ways to interact with constrained environments. Such advanced solvers could replace local propagation in our system for the maintenance of numerical relationships.