Pavane: A System for Declarative Visualization of Concurrent Computations

This paper describes the conceptual model, specification method, and visualization methodology for Pavane-- a visualization environment concerned with exploring, monitoring, and presenting concurrent computations. The underlying visualization model is declarative in the sense that visualization is treated as a mapping from program states to a three-dimensional world of geometric objects. The latter is rendered in full color and may be examined freely by a viewer who is allowed to navigate through the geometric world. The state-to-geometry mapping is defined as a composition of several simpler mappings. The choice is determined by methodological and architectural considerations. This paper shows how this decomposition was molded by two methodological objectives: (1) the desire to visually capture abstract formal properties of programs (e.g. safety and progress) rather than operational details and (2) the need to support complex animations of atomic computational events. All mappings are specified using a rule-based notation; rules may be added, delated, and modified at any time during the visualization. An algorithm for termination detection in diffusing computations is used to illustrate the specification method and to demonstrate its conceptual elegance and flexibility. A concurrent version of a popular artificial intelligence program provides a vehicle for demonstrating how we derive graphical representations and animation scenarios from key formal properties of the program, i.e., from those safety and progress assertions about the program which turn out to be important in verifying its correctness