Usability principles

From http://www.redhat.com/magazine/002dec04/features/usability/

User Knowledge Principle:

Figure out who your user is, what they do, and what they need.

Feature Bloat Principle:

Recognize the cost of each feature you add and each exceptional use case you accommodate.

Focus Principle:

Good design requires editing. Focus the design on one principle class of users.

Abstraction Principle:

Keep track of the “conceptual model” your software requires, and work at making it simpler. Reduce cognitive friction.

Direct Manipulation Principle:

Enable the illusion of direct manipulation when there is a reasonable physical metaphor.