Following on from my previous post about Design, Norman divides good design into 4 stages:
- Visibility - simply looking at something (with no direct knowledge of how it works) gives the user the state of the device and the alternatives for action.
- Conceptual Model - a 'model' designed into the operations of a device to give the user a coherent and consistent image of functionality.
- Mappings - making it easy to determine the relationships between actions and results, between the functions and their effects.
- Feedback - the user receives full and continuous feedback about the results of their actions.
The only one I would add though, would be 'Tone'. Tone is almost the physical manifestation of each of the above four ideas. It's really the 'aesthetic' delivered in a consistent and coherent manner.
For the innately visible aspects of design (visibility, feedback, even mappings) it's easy to see the importance of Tone - all great products have it. But for certain products, I think you can even extend the idea to the Conceptual Model. It's about having an elegant, or easy, or recognizable, or familiar (a subtle difference) idea running through a product.
Every PC has a basic conceptual model regarding how files are stored - folders. It's a very structured, almost rigid idea that lends itself to very linear thoughts (file size, position in hierarchy, order, etc.). If you use Google Desktop, the conceptual model of 'folders' is replaced by 'search' - files now have relationships to other files based on commonalities of content and meaning, not a position in a hierarchy. 'Search' is less structured, more fluid, less linear.
Conceptual Models thus have 'tone'. Either one may be appropriate. Which one fits best with the design you have?
All of this is Branding - well removed from what many people typically believe Branding to be all about - but Branding nonetheless.