Abstract: A dynamic visual presentation animates how classes or objects send messages and relate to each other in an object-oriented program during the program's execution. The presentation depicts classes or objects as graphical nodes on a computer display. The relative proximity of these nodes varies to reflect a specific relationship between classes or objects: either communication, creation frequency, or aggregation. Communication between objects is also dynamically depicted as a set of one or more line segments each passing through two or more of the nodes that have classes of methods on a call stack. Mapping these conceptual relationships into dynamic, spatial relationships makes them explicit and observable, allowing a user to better understand, debug, and tune the object-oriented program.