The seven of interfaces

The magic number seven has had its influence on programming methods but it has had less influence on the user interface where it is just as important.

If you have ever watched a TV program or movie that uses the multi-shot technique - multiple small panels showing different action at the same time - you might have admired the technique but why aren't all such programs made like this?

The answer it that it takes a lot of processing power to cope with a multi-screen bombardment - and sadly the vast majority of people just can't cope.We run out of bandwidth well before the theoretical seven strands of narrative. No, the average viewer likes a nice simple, single-thread storyline - with one image following another preferably in a correct time sequence.

If you agree with the last statement then think for a moment what this means for interfaces based on  hypertext, multi-media and GUIs in general. A typical web page crammed with links and is a clear example of where the human processing channel is threatened with imminent swamping by excess information. In the case of followable links the swamping is a drawn-out sort of affair as the user follows multiple threads of information and forgets what the original enquiry was all about. In the case of multi-media the swamping can be immediate; more like a tidal wave of information. To watch on-screen video and try to read text and listen to the audio tracks can be thrilling but it can also send the innocent who actually try to cope with the information into terminal overload.

Then there is the question of the rich GUI interfaces we can create so easily using any of the many technologies that give us far more than buttons. We tend to create interfaces that have the "gee whizz" effect and we can't help but be impressed by the clever implementations using any of the latest techniques -  overload is now the norm.

In fact as programmers we suffer from being too close to the interface. Our unit of comprehension is too large and we manage to cope by being immersed in the system so that we understand it in much larger grouping.

There are two ways in which acknowledging the human information processing limit can help us produce better interfaces. The first is to recognise that, no matter how complicated the display the focus of attention will rarely manage to cope with more than one or two things at any moment. In the same way you shouldn't nest control structures too deeply in a function, you shouldn't nest dialog boxes, menus  or windows too deeply. It is better to think in terms of a single focus of attention within your application. If the user opens multiple applications and so splits the focus, well that's up to them - perhaps they can cope. 

Overload and bloat

If you want to see an example of a program that breaks these rules then look no further then the standard Windows 7 file manager - Windows Explorer. It has at least three menus structures on show  - the two horizontal menus, and the task panel to the left. If you throw in the right-click context menu and any number of optional extras then you begin to realise that the user is overloaded. What menu to use for any particular task is a mystery.

Most of the existing Windows interface is like this. It has accreted alternative ways of doing things as we have succumbed to the need to add the latest interface widget or to simply improve by adding rather than improve by making better.When you throw in the need for backward compatibility you can appreciate that interfaces naturally grow from simplicity to overload.

You can apply the same accretion of complexity argument to just about everything in programming. It happens in language design

• C was a nice simple language but C++ grew beyond  simplicity
• C#  was light but  C# 3.0 is bloated.

It happens in application programming as versions gain new features and still retain the old. It happens in operating systems as they struggle to remain compelling at each upgrade while striving to still run the old stuff.

At every stage software adds complexity and outgrows the human channel capacity in every possible way.

The idea of a human as an information channel may have gone out of fashion in psychology but it is the only relevant model for software design.

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