Direct Manipulation

Shneiderman [54] defines ``direct manipulation interfaces'' as those which achieve three outcomes:

• Continuous representation of the objects and actions of interest
• Physical actions or presses of labelled buttons instead of complex syntax
• Rapid incremental reversible operations whose effect on the object of interest is immediately visible

The best way to understand direct manipulation is by way of example. A particularly simple example can be seen in [9,26], where the Macintosh graphing calculator is used to rewrite symbolic algebra. By dragging a subterm around an expression, the expression is updated to show its form after the valid application of rewriting rules.

Due to the immediacy and directness of this style of interaction, once novices have seen how to achieve simple tasks they often quickly warm to the style. Terse error messages may be avoidable, by preventing actions which imply invalid operations, removing a major source of frustration.

Proof-by-pointing is the most obvious application of direct manipulation to the domain of proving.