Usability defines the extent to which a product, system or service can be used by specific users to achieve specific goals with learnability, efficiency, memorability, errors and satisfaction in a specific context of use.
Good usability is not noticed at all by the user - like good typography of a book, a poster or a website.
Let's take a look closer at the five quality components of usability:
Heuristics, a form of cognitive strategy, have been studied in discplines such as cognitive psychology, social psychology and social cognition.
Heuristics are rules of thumb for reasoning, a simplification, or educated guess that reduces or limits the search for solutions in domains that are difficult and poorly understood.
Unlike formal structures like algorithms, heuristics do not guarantee optimal, or even feasible, solutions and are often used with no theoretical guarantee.
The system should always keep users informed about what is going on, through appropriate feedback within reasonable time.
The system should speak the users' language, with words, phrases and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in a natural and logical order.
Follow real-world conventions
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.
Support undo and redo
Users should not have to wonder whether different words, situations, or actions mean the same thing.
Follow platform conventions
Even better than good error messages is a careful design which prevents a problem from occurring in the first place. Either eliminate error-prone conditions or check for them and present users with a confirmation option before they commit to the action.
Minimize the user's memory load by making objects, actions, and options visible. 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.
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. Allow users to tailor frequent actions.
Provide actions for both, inexperienced and experienced users
Dialogues should not contain information which 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.
No irrelevant or rarely needed information
Error messages should be expressed in plain language (no codes), precisely indicate the problem, and constructively suggest a solution.
Express errors in plain language, provide solutions
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, focused on the user's task, list concrete steps to be carried out, and not be too large.
Focus on the user’s tasks, list concrete steps