The incorporation of figure captions in interactive systems is a new approach to enhance the usability of visual interfaces. Figure captions in a narrow sense--captions that describe images previously generated--were first developed by Mittal et al.\ [14]. This work has been carried out in the context of the SAGE-project, where complex diagrams are generated. Mittal et al. argue that users can deal with more complex diagrams if they are accompanied by explanatory captions. In other words: complex relations that must be depicted in several images (without captions) can be integrated in one diagram when explained appropriately.
Some systems produce what we introduced as instructive figure captions (recall Section 3). In particular, in the WIP project (Knowledge Based Information Presentation [34]) and in the COMET project (COordinated Multimedia Explanation Testbed [6]) technical illustrations and textual descriptions are generated to explain the repair and maintenance of technical devices. The content of their accompanying texts often goes beyond the content of the figure. The textual components are generated based on large knowledge bases, describing object properties and actions. To realize instructive figure captions, an explicit representation of actions is required. However, it is time-consuming to create those representations. Thus, practical realizations have a restricted application domain.
The selected content is presented within different media (graphics, animation and text) which are used either complementary or redundantly. The redundant information presentation aims at reinforcing the message, e.g. by appropriate cross-references. In this media selection process, the suitability of a medium to convey information is considered. Moreover, sophisticated media coordination facilities are employed.
This situation is considerably different from the problem we describe here in this paper. In contrast to these systems, we target at the interactive exploration of visualizations and not at a final presentation. Furthermore, in these systems graphics and text generation mutually influence each other.