End-user specification of interactive displays.

Presenting data graphically can often increase its understandability--well-designed graphics can be more effective than a tabular display of numbers. It is much easier to get an understanding of the relationships and groupings in data by looking at a pictorial representation than at raw numbers. Most visualization systems to date, however, have allowed users to only choose from a small number of pre-defined display methods. This does not allow the easy development of new and innovative display techniques. These systems also present a static display--users cannot interact with and explore the data. More innovative displays, and the systems that implement them, tend to be extremely specialised, and closely associated with an underlying application. We propose techniques and a system where the user can specify most kinds of displays. It provides facilities to integrate user-input devices into the display, so that users can interact and experiment with the data. This encourages an exploratory approach to data understanding. Most users of such systems have the sophistication to use advanced techniques, but conventional programming languages are too hard to learn just for occasional use. It is well known that direct manipulation is a powerful technique for novice users; systems that use it are much easier to learn and remember for occasional use. We provide a system that uses these techniques to provide a visualization tool. Extensions to the WYSIWYG (What You See Is What You Get) metaphor are provided to handle its shortcomings, the difficulty of specifying deferred actions and abstract objects. In the data graphics domain, the main drawbacks of WYSIWYG systems are the difficulty of allowing a variable number of data items, and specifying conditional structures. This system also encourages re-use and sharing of commonly used display idioms. Pre-existing displays can be easily incorporated into new displays, and also modified to suit the users' specific needs. This allows novices and unsophisticated users to modify and effectively use display techniques that advanced users have designed