User Interface Definition

A user interface is a linkage between a human and a device or system that allows the human to interact with (e.g., exchange information with) that device or system.

An interface is a shared boundary or connection between two dissimilar objects, devices or systems through which information is passed. The connection can be either physical or logical.

For example, the user interfaces of transportation vehicles (e.g., automobiles, locomotives and airplanes) typically consist of windows1, one or more instrument panels and a variety of controls that are operated with the hands and feet. The instrument panels increasingly include one or more electronic display monitors similar to those used with computers.

A user interface on a computer typically consists of a display device, a keyboard and a mouse. There are two common types of user interfaces on the display device: the command line interface (CLI), which contains text only, and the graphical user interface (GUI), which also includes images (e.g., windows, icons and menus).

Most GUIs employ a desktop metaphor, that is, resemble a desktop with folders, files, pictures, etc. that can be moved around, resized and otherwise manipulated. However, web browser-based user interfaces have been becoming increasingly common.

Sound also plays a role in user interfaces on personal computers. It has been common for many years for a simple beeping sound to be emitted in some situations, such as in the event of a user error. Software is widely available that can convert text to spoken words, and recent years have seen much improvement in speech recognition technology that allows computers to understand spoken commands.

Much progress has also been made on tactile user interfaces that provide feedback to users. An example is devices which consist of a matrix of fine diameter rods whose heights can be adjusted to represent visual images. Such devices are particularly useful for people with impaired vision.

A virtual reality user interface is one that simulates reality with, for example, a wrap-around display screen or special goggles together with realistic sound, vibration, temperature, smells, etc. This type of interface has been becoming increasingly sophisticated and its use has been growing rapidly for a wide variety of applications ranging from games to training for professionals (e.g., surgeons and aircraft pilots).

Designing user interfaces is a very important part of total product planning because it is a major factor in usability (i.e., how ease or difficult it is to use a product) and thus in both the commercial success of products and their safety. However, it is also a very challenging part because the required skill sets are usually very different from those used for other aspects of product development (e.g., writing software) and because human variability (i.e., the great differences in physical and mental characteristics among people) makes it difficult to create interfaces that will be suitable for all, or even most, users.

1These are, of course, real windows made of glass that allow the vehicle operator to see outside of the vehicle, and they should not be confused with the metaphoric windows that are used in GUIs on computer display screens.

Created December 2, 2005.
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