A human-to-computer
user interface
In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...
is said to be "reactive" if it has the following characteristics:
#The user is immediately aware of the effect of each "gesture". Gestures can be
keystroke
In programming and software design, an event is an action or occurrence recognized by software, often originating asynchronously from the external environment, that may be handled by the software. Computer events can be generated or triggere ...
s,
mouse clicks,
menu
In a restaurant, the menu is a list of food and beverages offered to customers and the prices. A menu may be à la carte – which presents a list of options from which customers choose – or table d'hôte, in which case a pre-established seque ...
selections, or more esoteric inputs.
#The user is always aware of the state of his/her data. Did I just save those changes? Did I just overwrite my
backup by mistake? No data is hidden. In a figure-drawing
program, the user can tell whether a line segment is composed of smaller segments.
#The user always knows how to get help. Help may be context-sensitive or modal, but it is substantial. A program with a built-in ''help browser'' is not reactive if its content is just a collection of
screen shots or menu item labels with no real explanation of what they do.
Reactivity was a major goal in the early user interface research at
MIT
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
and
Xerox PARC
PARC (Palo Alto Research Center; formerly Xerox PARC) is a research and development company in Palo Alto, California. Founded in 1969 by Jacob E. "Jack" Goldman, chief scientist of Xerox Corporation, the company was originally a division of Xero ...
.
A computer program which was not reactive would not be considered ''user friendly'' no matter how elaborate its presentation.
Early
word-processing programs whose on-screen representations look nothing like their printer output could be reactive. The common example was
WordStar
WordStar is a word processor application for microcomputers. It was published by MicroPro International and originally written for the CP/M-80 operating system, and later written also for MS-DOS and other 16-bit PC OSes. Rob Barnaby was the so ...
on
CP/M. On-screen, it looked like a
markup language in a character cell display, but it had deep built-in help which was always available from an on-screen menu bar, and the effect of each keystroke was obvious.
User interfaces
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