can be broken down into the following goals:

• Effectiveness – How accurately and completely users can
  accomplish tasks
  
• Efficiency – How quickly users can complete tasks
  
• Safety – Avoid dangerous situations caused by interaction with
  technology
  
• Utility – Provide enough functionality for users to accomplish
  necessary tasks
  
• Learnability – How easy is it to learn to use technology
  
• Memorability – How easy is it to remember how to use a
  technology once you have learned how to use it