Usability is a quality attribute
that assesses how easy user interfaces are to use. The word "usability" also
refers to methods for improving ease-of-use during the design process.
Usability is defined by five quality components:
Learnability: How easy is it for users to accomplish
basic tasks the first time they encounter the design?
Efficiency: Once users have learned the design, how
quickly can they perform tasks?
Memorability: When users return to the design after a
period of not using it, how easily can they reestablish proficiency?
Errors: How many errors do users make, how severe are
these errors, and how easily can they recover from the errors?
Satisfaction: How pleasant is it to use the design?
There are many other important quality attributes. A key one is utility,
which refers to the design's functionality: Does it do what users need?
Usability and utility are equally important: It matters little that something is
easy if it's not what you want. It's also no good if the system can
hypothetically do what you want, but you can't make it happen because the user
interface is too difficult. To study a design's utility, you can use the same
user research methods that improve usability.
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