CP-VIZ: An Open Source Visualization Platform for CP

Visualization is one of the best techniques for understanding the behaviour of constraint programs, allowing us to directly observe the impact of changes by visual inspection instead of using tedious debugging. So far, most constraint visualization tools have been closely linked to specific solvers, making it difficult to compare alternative solvers and to reuse development effort spent on other systems. Previous attempts [1] at generic tools were unsuccessful largely due to the complexity of the specification. The new, light-weight CP-VIZ system provides a simple XML based interface for solvers, and can be easily extended for new systems and constraints. In CP-VIZ, we try to visualize the search tree and the state of variables and (global) constraints in parallel views. The search tree shows choices, assignments and failures, modelled on the tree display in the OZ Explorer [3] and later in CHIP [4]. Constraints and variables are shown in a 2D layout defined by the user, individual global constraints are shown in custom visualizations similar to [5]. A new constraint can be added to the package by deriving a new class with a custom drawing method. The design of the visualization tool was driven by user-requirements, coming mainly from the development of an ECLiPSe ELearning course.