Myers provides a well-written discussion of a model for describing interactions with highly interactive, graphical, direct manipulative input devices. This model has been implemented as part of the Garnet user interface development environment at CMU. It allows for the specification and implementation of interactive behaviors separate from considerations of graphics and application programs.

The key idea is that interactive behaviors are categorized by, and encapsulated in, a set of “interactor” object types. The six types of interactors are menu interactor, move-grow interactor, new-point interactor, angle interactor, text interactor, and trace interactor. Although no widely accepted taxonomy of input operations is extant, these six interactors seem to cover most input operations that are possible with a keyboard and a mouse. Interactor parameters (described in the paper) allow the interactions to be customized for many purposes. Default parameters handle common uses; a constraint-driven interface to application programs is provided for more complex behaviors.

One of the best features of this paper is that Myers’s description of this model for handling input is well illustrated and therefore quite understandable. It is replete with examples and sample screens. This paper would be useful for researchers in computer system interfaces as well as professional developers of such interfaces. The reference list provides a useful summary of related work.