The decision to run an application exclusively on a device has many implications for functionality and interaction. For safety-relevant devices, it may be an improvement of safety.

Context

This is an issue in the design of every application.

Forces

The nature of usage of this application is transient, i.e., users turn to the device to perform tasks, and then turn back to their main screens to continue working. Therefore, visual design must be unambiguous, colours must be used for easy visibility, and the entire application must be simple to use. Running on an embedded device, extra consideration must be given when applying computer metaphors (e.g. using a “desktop”) to the user interface.

Solution

The voice communication application under evaluation differs from conventional desktop software in several respects: First, it runs on a custom-built device under Windows XP Embedded equipped with a handset and a few bezel buttons to complement the 10 to 12 inch touch screen. The users of this device are no computer experts and can be considered novices and intermediates. The nature of tasks the device supports implies that it is used only on occasion, e.g., when a call comes in or must be made. Borrowing from Alan Cooper’s terminology, this means the application is transient and works to support the signalling system, a set of applications with sovereign posture.

Nonetheless, the device supports a wide variety of functions, e.g., sending messages and broadcasts to trains. The interface is not explorational but offers functions on a limited path; therefore, it is transactional. Following Cooper’s recommendations for the design of kiosk systems, special consideration was given to the size of controls, to input using a virtual keyboard, and to the use of selection mechanisms like drag and drop [1]. The application unites characteristics of the two most common postures, sovereign and transient, how- ever, a new term has been coined to describe the posture of this interface, called “exclusive full-screen posture”.

The solution proposes to let the application use the entire screen and be the only application running on the embedded device. Cooper mentions guidelines for the design of embedded devices:

Usability Impact

Error prevention, user satisfaction

Safety Impact

Using the exclusive full-screen posture prevents safety-relevant functions from being covered by other application windows.

Usage

Has been used in several European railways voice communication devices.

References and Literature

A. Cooper, R. Reimann, and D. Cronin. About Face 3.0 – The Essentials of Interaction Design. Wiley Publishing Inc, 2007

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