So far we have said little or nothing about usability. The previous section described how software systems get built, but not how usable software systems get built. What would be appealing to software developers would be a new box in the waterfall model called ‘design for usability’ in which the software or designs they have so far developed are passed along to a set of usability experts, who perform their own special rituals to the designs and pass them back into the process, guaranteed to result in improved usability.

The idea of user interface management systems (UIMS for short) is one way of appealing to this idea. UIMS assume that functionality can be separated away from the interface, so software developers can get on with developing their functionality while not worrying about how users make use of that functionality, while interface experts beaver away at designing interfaces that make that functionality easy to use.

Its a beguiling idea, but misguided. Consider the following example:

The Mini is a classic small car, revolutionary in its day and affectionately remembered by most people who owned one. Early models were very spartan in design and manufacture. The speedometer, fuel gauge and other indicators were housed together in a single circular unit which was placed centrally on the dashboard. (Whether this was to make production costs cheaper because the unit stayed in the same place no matter if the car was left or right hand drive is not clear, but it seems likely.) Unfortunately if a moderately tall driver were to use the car they would find that the hand gripping the steering wheel when the car was moving straight forward almost entirely blocked the view of the speedometer and other gauges. To see the gauges the driver would have to take his hand off the steering wheel; not a recommended activity.

Now given that design, the car’s manufacturers could have brought in the most skilled designers to improve the readability of the gauges, but it would not have made the slightest difference. The most well designed gauges in the world are useless if they cannot be easily seen.

The parallel for usability design is clear. If the functionality is inadequate or inappropriate for a given task, the most well designed interface is not going to mitigate that fact at all. Good user interfaces can make good functionality usable, but the functionality needs to be designed for the user too. Therefore user centred design needs to permeate through all the steps of the waterfall model.

The following is very important and should be taken to heart by all usability experts:

Good usability takes more than a good user interface.

Note however that the equating of usability with interface design is deeply ingrained. Even one of the recommended texts for this course seems to make this fundamental error from the outset: Shneiderman’s ‘Designing the user interface’. (This not to say that there is not a wealth of useful information in Shneiderman’s book, but it has an awful title.)