Uncle Bob listed a few Design smells — the odors of rotting software in his book Agile Software Development. Take the inverse of that and what do you get? Criteria for good design — that’s the approach that the author of the book PHP in Action took.

Here are the characteristics of good design.

1. Flexibility – easy to change
2. Robustness – hard to break
3. Mobility – easy to disentagle into reusable components
4. Fluidity – easy to do things right
5. Simplicity
6. Once and only once
7. Transparency – easy to read and understand

Very good criteria, in my opinion.