Off-screen visualization techniques for class diagrams

Visual representations of node-link diagrams are very important for the software development process. In many situations large diagrams - probably consisting of hundreds of nodes and edges - have to be edited and explored. In state-of-the-art modeling tools these activities are often accompanied by time consuming panning and zooming. In this paper we contribute the application of off-screen visualization techniques to the domain of node-link diagrams in general and to UML class diagrams in particular. The basic idea of the approach is to give a contextual view of all nodes which are clipped from the current viewport. Nodes are represented by proxy elements located within an interactive border region. The proxies show information of the associated off-screen nodes and can be used to quickly navigate to the respective node. However, there are several challenges when this technique is adapted to node-link diagrams, for example concerning the change of edge routing or scalability. We describe the design space of this approach and present different visualization and interaction techniques in detail. Furthermore, we conducted a formative evaluation of our first prototype. Based on the observations made during the evaluation, we came to final suggestions how particular techniques should be combined.