User-Centred Requirements Handbook

The following set of general guidelines may be used for the development of the user interface to the proposed system. Before starting the design, it is recommended that this section be reviewed and key phases highlighted. This will form a simple checklist which will act as a reminder of the main general aims of the design.

It is easy to overestimate peoples' ability to use systems. Aim to keep the basic interface simple offering facilities which are of clear value to potential users. Provide the most important facilities on separate keys. Those facilities that are infrequently used or are seen as 'value-added' should be shielded from the unsophisticated user for access via a menu or key combination.

Due to the inherent complexity of the human interaction with many systems, a structure needs to be imposed upon the user dialogue in order to guide the user through it. However, such structures often seem to place barriers on the person's usage and make the device seem inflexible and unusable. Therefore specify access facilities that take into account the kinds of paths that people will wish to follow. Make it very convenient to change modes so that the user should not need to close down one activity in order to start another. Clearly interface design could become very complex, so limits have to be placed on such movements.

The user should feel that they are in control and that the system is responding to his or her actions, not vice versa. Care should be taken to ensure that the user does not feel paced by the system, a common problem with systems making excessive use of time-outs. Users should have control over the amount of information they receive at different points of the interaction.

Sequences of actions should generate the expected response, identical terminology and abbreviations should be used throughout, prompts should always appear in the same place. However total consistency cannot always be achieved. For example it may be made easier to recall a stored number on a telephone by simply pressing one key to recall its memory location, compared with the user having to enter a leading zero when storing in memory.

Frequent use brings with it the desire to reduce the number of interaction steps and to speed up the interaction process. Macro facilities, special key combinations and 'fast path' keys and links are useful additions to the system, but only if their presence does not interfere in any way with the dialogue as presented to a novice user.

The screen layout should give an appearance of clarity with white space used to separate items. The items on the screen should be grouped together appropriately and sequence in a logical order. Human short-term memory limits are generally taken to be 'seven plus or minus two' chunks of information. Displays should be kept simple and users should not be required to 'carry-over' information from one display to another.

Every operator action should elicit some system feedback. At its simplest this might be a click to confirm a key press. Providing no feedback can lead the user to believe that no action has taken place. It is very important to give feedback at the end of a sequence or operations to give the user the satisfaction of reaching task closure. Also provide prompts to guide the user through the interaction sequence. The user should never be left in the state of not knowing what to do next. Messages should be constructive and give guidance for using the system in a courteous way. All messages should be part of the system design and available in the user manual.

The user should not be able to damage the equipment or make serious error. Destructive commands such as deleting a directory or erasing all memories should be structured such that the user is made to confirm his action. Inapplicable commands should leave the system state unchanged. Ideally, any action should be 'undoable' or reversible, so that a user does not fear learning by experimentation, though this is often difficult to implement.

The user will generally have the need to carry out tasks as quickly as possible. Bear in mind, when producing a design, what time and effort the user will be prepared to put into achieving their goals with the system.

Help facilities should be easily accessible. The user should not have to spent a long time reading the help in order to use the system or to overcome problems. Therefore help text should be quick and easy to read. Where possible provide context sensitive help so that the help relates to the current point within the system. Help should also be task oriented so that it explains actions in terms of the tasks the user may wish to perform. Allow the system to be used while help remains displayed and avoid obscuring crucial parts of the screen with the help window.

Appendix 2 - Human Factors Standards
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