Incremental Layout in DynaDAG

E ective techniques have been developed for some important families of graph layouts, such as hierarchies, planar embeddings, orthogonal grids and forced-directed (spring) models [1]. These techniques have been incorporated in practical user interfaces that display static diagrams of relationships between objects [19, 18, 17]. Static diagrams are not completely satisfactory because in many situations, the displayed graphs can change. Three common scenarios are: Manual editing. Most interactive graph drawing systems allow users to manually insert and delete nodes and edges. Layouts must be updated dynamically to re ect such changes. Browsing large graphs. When only static layout is available, browsing large graphs usually means drawing the entire graph and then viewing portions in a window with pan and zoom controls, sheye lenses, etc. The problem is that the section in the current window may not be very informative. For example it may contain edge segments whose endpoint nodes are outside the window, or nodes whose placement can be rationalized globally but not locally. Incremental layout o ers the alternative of directly adjusting the set of displayed objects to make informative displays. Visualizing dynamic graphs.Often, data being visualized is subject to change. In our experience with the dotty system, we found many applications for graph animations: