Hierarchical diagrams are well-suited for visualizing the structure and decomposition of complex systems. However, the current tools poorly support modeling, visualization and navigation of hierarchical models. Especially the line routing algorithms are poorly suited for hierarchical models: for example, they produce lines that run across nodes or overlap with other lines.

In this paper, we present a novel algorithm for line routing in hierarchical models. In particular, our algorithm produces an esthetically appealing layout, routes in real-time, and preserves the secondary notation of the diagrams as far as possible.