Conclusions

This dissertation has presented a working design for a new style of user interface development system called ``Pad''. Just as certain elements are combined to create the Desktop interface, this new style interface has several distinguishing characteristics:

• It is a zoomable system, all data objects exist in a two dimensional floating point coordinate system,
• applications adopt a ``work-through'' mechanism, meaning that they adopt the metaphor of a transparent filter which is placed over the objects upon which they are to operate,
• a meaningful and consistent semantics is provided for the composition of multiple filters.

By adding these capabilities to the user interface substrate underlying the system's applications, it gives the applications a different flavor than those of conventional systems such as Microsoft Windows. It is expected that applications will tend to be of a finer granularity and greater number, each one