Heuristics

• Simple and natural dialogue: Dialogues should not contain information that is irrelevant or rarely needed. Every extra unit of information in a dialogue competes with the relevant units of information and diminishes their relative visibility. All information should appear in a natural and logical order.

• Speak the users' language: The dialogue should be expressed clearly in words, phrases, and concepts familiar to the user, rather than in system-oriented terms.

• Minimize the users' memory load: The user should not have to remember information from one part of the dialogue to another. Instructions for use of the system should be visible or easily retrievable whenever appropriate.

• Consistency: Users should not have to wonder whether different words, situations, or actions mean the same thing.

• Feedback: The system should always keep users informed about what is going on, through appropriate feedback within reasonable time.

• Clearly marked exits: Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue.

• Shortcuts: Accelerators - unseen by the novice user - may often speed up the interaction for the expert user such that the system can cater to both inexperienced and experienced users.

• Good error messages: They should be expressed in plain language (no codes), precisely indicate the problem, and constructively suggest a solution.

• Prevent errors: Even better than good error messages is a careful design that prevents a problem from occurring in the first place.

• Help and documentation: Even though it is better if the system can be used without documentation, it may be necessary to provide help and documentation. Any such information should be easy to search, be focused on the user's task, list concrete steps to be carried out, and not be too large.